4 Mycobacterium and Mycelial Bacteria (54)

Question 1

Case
A 45-year-old woman presents with a deep subcutaneous abscess on her back. She received acupuncture treatment for chronic leg pain at a clinic a few weeks earlier; the abscess developed at one of the acupuncture sites. Surgical drainage is done, and the purulent material is sent for microscopy and culture. Gram stain of the material shows faintly-staining Gram-positive filamentous bacilli with a beaded appearance. Ziehl-Neelsen stain shows the presence of acid-fast bacilli. Cultures are put up for common pyogenic bacteria, as well as for mycobacteria. Within 7 days, grayish-white colonies of acid-fast bacilli (AFB) appear on aerobic blood agar and Lowenstein-Jensen medium. The organism grows both at 30° and 37°C, with a better growth at 30°C. It is resistant to many antibiotics, including first-line antituberculosis drugs. The patient is treated with oral clarithromycin. With surgical drainage and a prolonged course of the antibiotic for 6 months, the patient is cured.

What is the most likely bacillus to have caused the infection?

1 Mycobacterium ulcerans
2 Multidrug-resistant Mycobacterium tuberculosis
3 Mycobacterium kansasii
4 Nocardia abscessus
5 Mycobacterium abscessus
6 Mycobacterium leprae

Answer 1

Mycobacterium abscessus

Mycobacterium abscessus belongs to the M. chelonae-abscessus group of rapidly growing mycobacteria (RGM). The microscopic features and the acid-fast nature of the organisms in the clinical specimen are suggestive of the species. It is possible to isolate the organism from the clinical sample within 7 days of incubation and observe growth using Lowenstein-Jensen medium. Production of non-pigmented colonies occurs, with enhanced growth at 30°C. These observations contribute to the identification of the isolate as a rapidly growing mycobacterium; among the options given, M. abscessus is the only rapidly growing mycobacterium.
M. abscessus is ubiquitous; it is found in soil and water worldwide. It is one of the most resistant species of the pathogenic RGM. It is involved in a variety of community-acquired and healthcare-associated infections. M. abscessus is known to cause severe pulmonary infections in patients with underlying chronic lung diseases (e.g., cystic fibrosis and bronchiectasis), nosocomial outbreaks of surgical wound infections, post-injection abscesses, and disseminated infections in hemodialysis patients. Amikacin, cefoxitin, and clarithromycin are the antibiotics found most useful in treating M. abscessus infections. Lung diseases are often difficult to cure, although clinical improvement can occur. Most strains of M. abscessus are resistant to the newer quinolones; the quinolones are useful for treating infections caused by M. fortuitum of the RGM species. Conventional biochemical and phenotypic identification methods are used in clinical laboratories for preliminary identification of an RGM species. Confirmatory tests based on molecular methods are done by reference laboratories. Polymerase chain reaction-based tests are used for the identification of M. abscessus.
Mycobacterium ulcerans is a slow-growing mycobacterium that grows within 8-12 weeks. It causes Buruli ulcer, an important health problem in West African countries. The disease is also known to occur in scattered foci around the world, including Melbourne, Australia. M. ulcerans is a ubiquitous organism and is harbored by fish, snails, and water insects. The mode of transmission is unknown. The organism requires a temperature of 32°C for growth. Mycobacterium ulcerans produces a potent polyketide toxin (mycolactone), thereby distinguishing itself from all other mycobacteria. The genetic code for mycolactone is carried by plasmid. Mycolactone causes extensive necrosis, which is characteristic of the disease, and destroys the cells in the subcutis; this causes the development of large ulcers with undermined edges. Bones may be affected, which leads to disabilities. Lack of early acute inflammatory response is a feature of an M. abscessus infection. The bacteria are primarily extracellular.
Multidrug-resistant M. tuberculosis is the most important human pathogenic mycobacterium. It is slow-growing; it takes 3-6 weeks for growth to appear on Lowenstein-Jensen medium. It does not grow at 30°C or on routine media (e.g., blood agar). A strain of M. tuberculosis is called multidrug-resistant when it is resistant to both isoniazid and rifampin, the 2 major first-line drugs used to treat tuberculosis. Tuberculosis caused by such strains is more difficult to treat and is associated with a high death rate in HIV-infected patients.
Mycobacterium kansasii is a photochromogen (i.e., producing pigment in the presence of light). It requires complex media and incubation at 37°C for growth. It is not a rapid grower. It can produce pulmonary and systemic infections indistinguishable from those caused by M. tuberculosis, especially in immunocompromised patients.
Nocardia abscessus is one of the recently described species belonging to Nocardia asteroides complex, which is the species most commonly associated with human disease. It possesses the morphological and cultural characteristics of Nocardia. On Gram stain, the organism appears as Gram-positive branching filaments. It is weakly acid-fast, (due to short-chained mycolic acid) and retains carbol fuchsin only with weak decolorizing agents (e.g., 1% sulfuric acid). With the standard Ziehl-Neelsen stain for mycobacteria, Nocardia appears non-acid-fast. The cells are partially acid-fast; only a proportion of cells from a culture show an acid-fast nature. The organism grows on a variety of media within 1 week or more, often producing pigmented colonies with aerial hyphae. Nocardia are normally found in soil and are known to produce opportunistic infections. Soft tissue infections can occur in healthy persons following percutaneous trauma.
Mycobacterium leprae, the organism causing leprosy, is typically acid-fast with irregular staining. The bacteria are arranged singly, in parallel bundles (or masses) called globi, in skin or mucous membrane scrapings of patients with lepromatous leprosy. Although the organism was described by Hansen in 1873, it has not yet been cultivated on inanimate (non-living) media. When inoculated into the footpad of a mouse, M. leprae produces local granulomatous lesions. In armadillos, it produces extensive lepromatous lesions. Wild 9-banded armadillos in the south and central United States are natural hosts of M. leprae, and infected armadillos constitute a large reservoir of the organism.

Question 2

Case
A 60-year-old woman with long-standing systemic lupus erythematosus (SLE) presents with a several-day history of fever, chills, and cough. She has received multiple courses of cyclophosphamide for lupus nephritis and was on prednisolone for a long time. A chest X-ray and CT scan are done; the results indicate the presence of nodular lesions in the lower lobe of the right lung with some evidence of cavitation. Sputum, as well as bronchioalveolar lavage (BAL), are sent for microbiological tests. In the laboratory, a Gram stain of the sputum and BAL smears show an abundance of leukocytes and a high predominance of Gram-positive, thin-branching filaments. Smears stained by Kinyoun’s acid-fast method are negative for acid-fast bacteria. A modified acid-fast stain using 1% sulphuric acid as a decolorizing agent shows the partial acid-fast nature of the filamentous branching bacteria in both clinical samples.

Assuming this organism as the etiological agent of this patient’s pulmonary disease, what antimicrobial agent is most likely to be used for her treatment?

1 Trimethoprim/Sulfamethoxazole (TMP/SMX)
2 Minocycline
3 Amikacin
4 Imipenem
5 Linezolid
6 Amphotericin B

Answer 2

Trimethoprim/Sulfamethoxazole (TMP/SMX)

The morphological characteristics of the organism are suggestive of the Nocardia species, which is a Gram-positive, branching filamentous bacterium possessing partial acid-fastness due to the presence of cell wall mycolic acids. Other Gram-positive bacteria with branching filamentous morphology (e.g., actinomyces and streptomyces) are non-acid-fast, even when stained by a modified acid-fast stain. Trimethoprim/Sulfamethoxazole (TMP/SMX) remains the antimicrobial of choice; it is the most commonly prescribed agent in the treatment of a Nocardia infection. The mechanism of action of TMP/SMX is by the 2 components TMP and SMX, sequential inhibiting enzyme systems involved in the bacterial synthesis of tetrahydrofolic acid (the metabolically active form of folic acid). This leads to the blockage of the synthesis of bacterial nucleic acid and proteins.
Nocardiosis is usually an opportunistic infection in persons with predisposing conditions (e.g., chronic pulmonary disease, long-term corticosteroid therapy, diabetes mellitus, hematological malignancies, transplantation, and AIDS). The most common clinical presentation of a Nocardia infection is pulmonary disease, which is acquired by inhalation. Pulmonary nocardiosis has a tendency for necrosis and may mimic conditions such as tuberculosis and neoplasm. The sources of Nocardia include soil, dust, and air containing fragmented Nocardia cells. There are several species of Nocardia; more than 30 species are associated with human infections. Most of the infections are caused by the Nocardia asteroids complex. Geographic variation has been observed regarding the prevalence of different species. Nocardia species may vary in their antimicrobial susceptibility patterns. Nocardia farcinica is reported to be one of the most drug-resistant species. Susceptibility testing is important, though time-consuming. Prolonged treatment is required as relapses may occur after short courses of therapy.
Minocycline, amikacin, and imipenem are primary agents and have been used successfully for treatment of Nocardia infections. One of these primary agents, in combination with a sulfonamide or trimethoprim/sulfamethoxazole (TMP/SMX), is recommended for complicated systemic infections. The combination of amikacin and imipenem is often used as empirical therapy for systemic Nocardia infections. Minocycline, which is a second-generation, long-acting tetracycline, and amikacin, a potent aminoglycoside, act by inhibiting bacterial protein synthesis. Imipenem is a broad-spectrum β-lactam antibiotic belonging to the class of carbapenems. It binds to the penicillin-binding proteins and disrupts cell wall synthesis; this causes the death of the microbial organism.
Linezolid is a newer synthetic antibiotic, the first of a new class of antimicrobial agents known as oxazolidones. It is used against resistant Gram-positive pathogens (e.g., MRSA and VRE). It is bacteriostatic, and its mechanism of action is unique. The drug interferes with the first step of bacterial ribosome assembly; this blocks the formation of an initiation complex. No other antimicrobial inhibits this process; therefore, there is no cross-resistance. Linezolid has been successfully used in serious and disseminated Nocardia infections, and it is considered a primary agent for the treatment of nocardiosis. The drug is generally well-tolerated; the most common adverse effects are gastrointestinal effects and headache. Prolonged administration of linezolid can lead to myelosuppression; this serious adverse effect is reversible after discontinuation of the drug.
Amphotericin B is an antifungal agent and not used for the treatment of nocardiosis. It is a polyene antibiotic and is a metabolite of streptomyces. The mechanism of action is by inhibiting cell membrane function, which involves the formation of complexes with ergosterol in fungal cell membranes. It is the most useful and effective drug for the treatment of severe systemic mycotic infections (e.g., cryptococcosis, coccidioidomycosis, histoplasmosis, aspergillosis, and candidiasis). This antifungal agent (in the form of amphotericin B deoxycholate) was the standard preparation used for several years. Recently, lipid formulations of this drug have been introduced and found to be more effective and safe. Liposomal amphotericin B, one of the lipid formulations, is also useful as a therapeutic agent for visceral leishmaniasis.

Question 3

A 72-year-old female served 3 years in an emerging nation as an international relief organization volunteer. Gradually, over this extended period of time, she developed facial skin deformities. They produced a somewhat leonine facies manifested by thickening of her skin, associated with some areas of numbness. You are seeing her for the first time after her return from her overseas volunteer duty. The etiologic agent is most probably which of the following?

1 Mycobacterium marinum
2 Mycobacterium avium intracellulare
3 Mycobacterium leprae
4 Mycobacterium kansasii
5 Mycobacterium gordonae

Answer 3

Mycobacterium leprae

Mycobacterium leprae is most reasonably associated with the combination of thickening of the skin and areas of numbness. This is Leprosy, also known as Hansen’s disorder. It is reasonable to examine her family members and her close contacts regularly for Leprosy. Diagnosis of leprosy should be considered when history of travel to tropics or endemic areas is present. The clinical presentation includes painless skin patch, paresthesias or loss of sensation where the affected peripheral nerves are distributed, muscle weakness and wasting, claw hand, foot drop, and ulcerations of hands or feet. Leonine facies is associated with lepromatous leprosy wherein the skin of the face becomes thickened and corrugated. Based on the physical findings, the subtypes of leprosy include tuberculoid, lepromatous, borderline tuberculoid, mid- borderline leprosy, borderline lepromatous, and indeterminate leprosy. Skin biopsy and nasal smear help demonstrate Gram positive, acid-fast bacilli. Management is by treatment with dapsone, rifampicin, and clofazimine.
Mycobacterium avium intracellulare is a systemic opportunistic infection most commonly seen in immunosuppressed patients such as in Acquired Immune Deficiency Syndrome (AIDS). Mycobacterium avium complex (MAC) consists of 2 species—M avium and Mycobacterium intracellulare. MAC infection usually presents in 3 forms, which include pulmonary MAC in immunocompetent hosts, disseminated MAC in individuals with advanced AIDS, and in children as lymphadenitis.
Mycobacterium marinum infection, manifested as “swimming pool granuloma or fish tank granuloma,” is seen following the exposure of normal, healthy individuals to either a swimming pool or a fish tank having sustained a recent superficial skin laceration or a recent superficial skin abrasion. Hence, normal healthy individuals would do well not swimming or cleaning fish tanks when they have just recently sustained a superficial laceration or a superficial abrasion. Patients generally present with a papule, nodule, or ulcer at the site of trauma following exposure to non-chlorinated water approximately 2-3 weeks earlier.
Mycobacterium kansasii is a blood borne opportunistic infection, commonly manifested in the lungs and is seen in immunosuppressed patients. Cutaneous lesions in immunocompetent individuals include nodules, pustules, verrucous lesions, erythematous plaques, abscesses, and ulcers.
Mycobacterium gordonae is found ubiquitously and is rarely, if ever, a pathogen. It may produce skin granuloma or nodule following injuries involving soil contamination. In HIV patients having severe immunosuppression, it may infect the lungs, blood, bone marrow, and other organs.

Question 4

Case
A 4-year-old boy presents with a mass in the neck. His mother works as mycobacteriology laboratory personnel. Physical examination of the child reveals non-tender discrete lymph nodes in the upper neck. Oropharyngeal examination is negative; so are the chest X-ray and tuberculin skin test using purified protein derivative (PPD). Cervical lymph node biopsy is advised. Biopsy report shows granulomatous lesion with central necrosis and special stain revealed presence of acid-fast bacilli.

Non-reactive PPD test in this child could be due to what?

1 BCG vaccination
2 Mother working as microbiology lab personnel
3 Cervical lymphadenitis from atypical mycobacteria
4 Undocumented past infection with M. tuberculosis
5 Cat scratch disease

Answer 4

Cervical lymphadenitis from atypical mycobacteria

Tuberculin skin test or purified protein derivative test is usually negative or non-reactive in infections with atypical mycobacteria. Tuberculin from atypical mycobacteria, such as scrofulin for M. scrofulaceum, has also been prepared and can be used for specific diagnosis. Cervical lymphadenitis due to atypical mycobacteria is responsible for this patient’s signs and symptoms. The diagnosis is scrofula (tuberculous cervical lymphadenitis). M. scrofulaceum, a slow-growing atypical mycobacteria, causes scrofula, which is a granulomatous cervical adenitis in children and is usually present unilaterally. Constitutional symptoms are usually absent. The organisms are resistant to the usual anti-tuberculous drugs. Spontaneous remission is seen at puberty; if treatment is mandatory, surgical excision is indicated.
BCG vaccination gives a false positive reaction and not a non-reactive reaction. After 10 years of BCG vaccination, the rate of false positives from BCG reduces considerably.
The PPD test value in children < 4 years exposed to adults at high-risk is considered to be positive when it is more than 10mm. The family history of his mother working as microbiology lab personnel is considered as a risk for the development of tuberculosis; therefore, a test value of more than 10mm is considered positive and is an indication for antituberculous drug therapy. This will not result in non-reactive PPD test.
Cat scratch disease may present with cervical lymphadenopathy, and aspiration biopsy may reveal caseous necrosis and microabscess formation. Presence of acid-fast bacilli is unusual.
A positive test reaction indicates past or present infection with M. tuberculosis.

Question 5

A 40-year-old Sudanese farmer presented with a 1-year history of swelling and multiple abscesses with discharging sinuses on his left foot. The discharge contained yellow granules. Microscopic examination of the granules showed presence of delicate thin, Gram-positive, non-acid fast, branching filaments about 1 micron wide. Aerobic culture of the material on Sabouraud’s dextrose agar grew smooth colonies in 7 days. The colonies later became powdery and cottony due to branching aerial mycelium and chains of spores. The organism did not grow anaerobically. Which of the following is most likely to be the etiological agent isolated?

1 Streptomyces somaliensis
2 Madurella mycetomatis
3 Actinomadura pelletierii
4 Madurella grisea
5 Pseudoallescheria boydii

Answer 5

Streptomyces somaliensis

The lesion on the patient’s foot has the characteristics of Mycetoma (Madura foot). There are 2 types of mycetoma, eumycetoma caused by filamentous fungi and actinomycetoma caused by actinomycetes, the filamentous bacteria. Infection often follows penetrating trauma through which the organisms enter.
All of the listed organisms can cause mycetoma.
In this patient, the granules containing thin branching filaments 1-micron wide is suggestive of actinomycetoma. Madurella mycetomatis, Madurella grisea and Pseudoalleschiria boydii are fungi and their filaments are septate and broader, about 4-5-micron wide. Streptomyces somaliensis and Actinomadura pelletierii are aerobic actinomycetes known to cause mycetoma. The color and consistency of the granules are helpful in identifying the causative agent. S.somaliensis produces yellow granules and A.pelletierii produces red granules. Therefore, Streptomyces somaliensis is the correct answer.
Granules in Madurella mycetomatis and Madurella grisea infections are black and Pseudallescheria boydii produce white granules.
S.somaliensis is one of the very few species of streptomyces associated with infections. Though extremely rare, invasive infections caused by S.somaliensis and other streptomyces species have been reported. These include pulmonary infections, catheter-related infections, bacteremia and endocarditis, pericarditis, brain abscess, and peritonitis (Refs: 2, 3, 6, 7).
Streptomyces somaliensis has been identified as one of the principal agents of actinomycetoma in South America, Africa, India, Mexico, Malaysia, and US (7).
Pseudoallescheria boydii
is the prevalent species causing eumycetoma in the US.
Laboratory diagnosis of actinomycetoma includes culture and identification of the etiological agent by biochemical tests and chromatographic analysis of cell wall components. Molecular techniques have been applied for identification of the actinomycetes, including streptomyces (Ref: 9).
Prolonged treatment with antibiotics is required for curing the condition. If therapy is begun early, actinomycetomas respond well to combination therapy with streptomycin, trimethoprim-sulphamethoxazole and dapsone. Successful treatment of actinomycetoma using combination of amikacin and rifampin also has been reported (Ref: 10).

Question 6

A 21 year old woman with multiple disfigured skin lesions appeared in a community hospital. The primary complains of the patient was loss of sensation of touch on fingers and toes. Physical examination revealed anesthetic skin lesions. Physician sent the skin biopsy for Acid Fast staining. The smear revealed Acid Fast Bacilli in large amounts. The most probable organism responsible for this type of lesion is:

1 Mycobacterium tuberculosis.
2 Mycobacterium leprae.
3 Mycobacterium bovis.
4 Mycobacterium avium.
5 Mycobacterium kansasii.

Answer 6

Mycobacterium leprae.

Leprosy is a chronic granulomatous disease caused by Mycobacterium leprae . The principle manifestation of the disease includes anesthetic skin lesions and peripheral neuropathy with peripheral nerve thickening. Presence of AFB and Lepromin test are used to confirm the diagnosis of leprosy.

Question 7

Which of the following vaccines is used by countries where tuberculosis is endemic?

1 DPT
2 BCG
3 TIG
4 MMR
5 Hib

Answer 7

BCG

Vaccination with attenuated Mycobacterium bovis (bacilli Calmette Guerin) is used in countries where tuberculosis is endemic. BCG vaccination reduces the incidence of tuberculosis if administered at young age but can not be used in immunocompromised patients.
DPT is Diphtheria- pertussis-tetanus vaccine that contains toxoids for diphtheria and tetanus and killed organisms for whooping cough (pertussis).
MMR is measles-mumps-rubella vaccine recommended for all children.
Hib vaccine is for Haemophilus influenza type b.
TIG is tetanus immune globulin used for nonimmunized patients with deep, dirty wounds.

Question 8

The most commonly isolated Mycobacterial pathogen resulting in disseminated infection in AIDS patients in the United States is

1 Mycobacterium marinum
2 Mycobacterium ulcerans
3 Mycobacterium scrofulaceum
4 Mycobacterium gastri
5 Mycobacterium avium-intercellular complex

Answer 8

Mycobacterium avium-intercellular complex

Mycobacterium avium-intercellular complex is isolated in soil, water, swine, and infected poultry. Patients with AIDS are at higher risk for disseminated disease with Mycobacterium avium-intercellular complex. It is the most frequently isolated mycobacterial pathogen from AIDS patients in the United States.
Mycobacterium scrofulaceum is mostly implicated in cervical lymphadenitis in children.
Mycobacterium marinum and Mycobacterium ulcerans are associated with cutaneous infections. This infection caused by Mycobacterium marinum are also called “swimming pool granulomas” since it is often caused after exposure of the skin to water.
Mycobacterium gastri is not implicated as a pathogen in human.

Question 9

Swimming pool granulomas are caused by

1 Mycobacterium avium
2 Mycobacterium scrofulaceum
3 Mycobacterium marinum
4 Mycobacterium kansasii
5 Mycobacterium gordonae

Answer 9

Mycobacterium marinum

Cutaneous infections caused by Mycobacterium marinum occurs as a nodular lesion that develops into ulceration or can spread along the lymphatics. This infection is often acquired from contaminated water and is called “swimming pool granulomas.”
Mycobacterium scrofulaceum is mostly implicated in cervical lymphadenitis in children.
Mycobacterium gordonae , often called tap-water bacillus is rarely associated with infections.
Mycobacterium kansasii and Mycobacterium avium are frequently associated with nontuberculous mycobacterial pulmonary disease in human.

Question 10

The most common cause of mycetoma in North, Central and South America is

1 Rhodococcus equi
2 Thermoactinomycetes
3 Nocardia otitidiscaviarum
4 Nocardia asteroides
5 Nocardia brasiliensis

Answer 10

Nocardia brasiliensis

Mycetoma is a chronic suppurative, granulomatous disease of subcutaneous tissue caused by traumatic introduction of the organism into subcutaneous tissue. It can be caused by dematiaceous and non dematiaceous fungi or bacteria.
Nocardia brasiliensis is the most common cause of mycetoma in North, Central, and South America.
Nocardia asteroids is commonly implicated in bronchopulmonary disease with a high predilection for hematogenous spread to the central nervous system or skin.

Question 11

Laboratory diagnosis of Nocardia includes

1 Aerobic, gram positive, non acid fast branched filaments
2 Anaerobic, weakly gram positive, non acid fast bacilli
3 Aerobic, gram negative, non acid fast bacilli
4 Aerobic, poorly stained filaments with gram positive intracellular beads and are partially acid fast bacilli
5 Anaerobic, poorly stained filaments with gram positive intracellular beads and are partially acid fast bacilli

Answer 11

Aerobic, poorly stained filaments with gram positive intracellular beads and are partially acid fast bacilli

Nocardia species are aerobic and colony gives appearance of bread crumbs. Gram staining of positive smears reveals poorly stained filaments with intracellular gram positive beads. These organisms are partially acid fast because cell wall contain short chain of mycolic acid.

Question 12

The antibiotic of choice for treatment of nocardiosis is

1 Penicillin
2 Sulfonamides
3 Streptomycin
4 Dapsone
5 Erythromyci

Answer 12

Sulfonamides

Sulfonamides are drug of choice for nocardiosis. It is combined with appropriate surgical intervention for draining and cleaning of abscess. Antibiotic therapy should be extended for 6 or more weeks. Nocardia are resistant to penicillin.

Question 13

Actinomyces are opportunistic pathogens that are

1 Non-spore forming, gram-negative facultative anaerobes
2 Non-spore forming, gram-positive bacilli and can be either anaerobic or facultatively anaerobic3 Non-spore forming, acid fast facultative anaerobes
4 Spore-forming, gram-positive, aerobic bacilli
5 Spore-forming, gram-positive bacilli and can be facultative or strict anaerobes

Answer 13

Non-spore forming, gram-positive bacilli and can be either anaerobic or facultatively anaerobic

Actinomyces are non-spore forming, gram-positive bacilli and can be either anaerobic or facultatively anaerobic. Microscopic examination of the specimens reveals gram positive thin branching bacilli along with sulfur granules.

Question 14

Actinomyces infection

1 Is always exogenous in nature
2 Occurs by physical exposure to the infected person
3 Occurs when mucosal barriers are disrupted
4 Can be transmitted via aerosols
5 Can be transmitted by external sources such as soil or water

Answer 14

Occurs when mucosal barriers are disrupted

Actinomycosis is endogenous in origin and infection occurs when mucosal barriers are broken.
Actinomyces is the resident flora of upper respiratory tract, gastrointestinal tract, and female genital tract. The disruption in mucosal barriers can result in actinomycosis, and the organism spreads throughout the body as a result of suppurative infection.

Question 15

Lumpy Jaw is caused by

1 Nocardia
2 Mycobacteria
3 Actinomyces
4 Streptomyces
5 Propionibacterium

Answer 15

Actinomyces

Lumpy Jaw is cervicofacial infection caused by Actinomyces. Cervicofacial infection can be manifested as an acute pyogenic infection or can be a painless process. Swelling of the tissue with fibrosis and scarring, accompanied by open draining sinus tracts along the angle of the jaw and neck, are seen.

Question 16

Laboratory diagnosis of Actinomyces involves detection of:

1 Gram negative rods and positive aerobic cultures
2 Gram positive branching bacilli along the periphery of the granules and positive anaerobic culture
3 Gram positive spore forming bacilli and positive aerobic culture
4 Gram negative branching bacilli along the periphery of the granules and positive aerobic culture
5 Acid fast bacilli and positive anaerobic cultures

Answer 16

Gram positive branching bacilli along the periphery of the granules and positive anaerobic culture

For Actinomyces detection, the specimen is collected from deep in the sinus tract. If sulfur granules are detected, it is crushed between two glass slides, stained, and examined. Actinomyces are thin, non-spore forming, gram positive, branching bacilli seen along the periphery of the granules. They can be isolated if cultured in anaerobic conditions for 2 weeks or more and are non-acid fast bacilli.

Question 16

Laboratory diagnosis of Actinomyces involves detection of:

1 Gram negative rods and positive aerobic cultures
2 Gram positive branching bacilli along the periphery of the granules and positive anaerobic culture
3 Gram positive spore forming bacilli and positive aerobic culture
4 Gram negative branching bacilli along the periphery of the granules and positive aerobic culture
5 Acid fast bacilli and positive anaerobic cultures

Answer 16

Gram positive branching bacilli along the periphery of the granules and positive anaerobic culture

For Actinomyces detection, the specimen is collected from deep in the sinus tract. If sulfur granules are detected, it is crushed between two glass slides, stained, and examined. Actinomyces are thin, non-spore forming, gram positive, branching bacilli seen along the periphery of the granules. They can be isolated if cultured in anaerobic conditions for 2 weeks or more and are non-acid fast bacilli.

Question 17

The commonly used antibiotic of choice for treatment of Actinomyces is

1 Rifampin
2 Streptomycin
3 Actinomycin
4 Penicillin
5 Dapsone

Answer 17

Penicillin

Penicillin is the antibiotic of choice. Actinomyces are uniformly susceptible to tetracycline, erythromycin, and clindamycin. Surgical debridement of the infected tissue should be carried out along with extended course of antibiotic therapy.

Question 18

The most common species of genus Streptomyces, causing mycetoma world wide, is

1 Streptomyces albus
2 Streptomyces rimosus
3 Streptomyces violaceruber
4 Streptomyces somaliensis
5 Streptomyces lavendulae

Answer 18

Streptomyces somaliensis

Streptomyces somaliensis is the most common species that causes mycetoma.
Mycetoma is also caused by Nocardia, Actinomadura, Actinomyces, and some fungi.

Question 19

The key test for the identification of Mycobacterium tuberculosis include

1 Positive niacin and negative nitrate reductase test
2 Positive niacin and negative urease test
3 Positive nitrate reductase and negative niacin test
4 Positive heat stable catalase test and positive niacin test
5 Positive niacin test and positive nitrate reductase test

Answer 19

Positive niacin test and positive nitrate reductase test

Key test for the definitive identification of Mycobacterium tuberculosis includes niacin and nitrate reductase tests, however it takes three weeks or more before the results are available.
Mycobacterium avium intercellulare complex is negative for niacin and negative for nitrate reductase test.
Mycobacterium tuberculosis gives positive niacin and positive nitrate reductase tests.

Question 20

Mycobacterium tuberculosis:

1 Is acid fast due to very low lipid content of cell wall
2 Is an obligate anaerobe
3 Has cord factor and sulfatide product, which contributes to virulence
4 Cannot survive inside normal macrophage
5 Produces endotoxins

Answer 20

Has cord factor and sulfatide product, which contributes to virulence

Mycobacterium tuberculosis is obligate aerobe and is acid fact due to very high lipid content. This organism does not produce endotoxins or exotoxins. Virulence factors possessed by the organism are the ability to survive in macrophages and the ability to form toxic product like cord factor and sulfatide product.

Question 21

Mycobacteria classified as Runyon group III are

1 Rapid growers and pigmented
2 Slow growers and pigmented
3 Able to produce pigment after exposure to light
4 Able to produce pigment in dark only
5 Slow growers and non pigmented

Answer 21

Slow growers and non pigmented

Runyon classified Mycobacteria into four groups based on their rate of growth and their ability to produce pigments in the presence or absence of light.
Runyon group I - produce pigment after exposure to light
Runyon group II - produce pigment in dark as well as in the light
Runyon group III - slow growers and non pigmented
Runyon group IV - rapid growers and non pigmented

Question 22

The criteria of positive skin test (PPD) in immunocompromised patient exposed to Mycobacterium tuberculosis is

1 Measurement of skin reactivity at 24 hours after intradermal inoculation of 10 μg of PPD
2 Reaction of 10 mm or more induration after intradermal inoculation of 0.1 μg of PPD when measured after 48 hours
3 Reaction of 10 mm or more induration after intradermal inoculation of 10 μg of PPD when measured after 48 hours
4 Measurement of skin reactivity at 72 hours after intradermal inoculation of 5 μg of PPD
5 No reaction after intradermal inoculation of 5 μg of PPD when measured at 48 hours

Answer 22

Reaction of 10 mm or more induration after intradermal inoculation of 0.1 μg of PPD when measured after 48 hours

Criteria for positive skin test in immunocompromised patients, HIV negative drug users, foreign born individuals, residents of long term care facilities includes the measurement of skin test reactivity at 48 hours after intradermal inoculation of 5 tuberculin units or 0.1 μg of PPD.
Reaction of 10 mm or more is considered positive.

Question 23

Hansen’s disease is caused by

1 Mycobacterium avium-intracellulare
2 Mycobacterium kansasi
3 Mycobacterium ulcerans
4 Mycobacterium leprae
5 Mycobacterium marinum

Answer 23

Mycobacterium leprae

Leprosy is also called Hansen’s disease and is caused by Mycobacterium leprae. Leprosy is spread by person to person contact. The clinical presentation of leprosy is subdivided into tuberculoid leprosy and lepromatous leprosy.
Mycobacterium avium-intracellulare and Mycobacterium kansasi cause localized pulmonary infections and disseminated infections.
Mycobacterium ulcerans and Mycobacterium marinum cause cutaneous disease.

Question 24

Patients with tuberculoid leprosy have

1 Very weak cellular response
2 Strong delayed hypersensitivity reaction
3 Strong humoral antibody response
4 Presence of large number of bacilli in Schwann cells of peripheral nerves
5 Presence of large number of bacilli in dermal macrophages

Answer 24

Strong delayed hypersensitivity reaction

Patients with tuberculoid leprosy have strong delayed hypersensitivity reaction but a weak humoral antibody response. This is characterized by large number of lymphocytes and granulomas and few bacilli are present in tissue because of the production of cytokines mediated macrophage activation, phagocytosis and bacillary clearance.
Patients with lepromatous leprosy have a strong antibody response but weak cellular response to Mycobacterium leprae antigens. Therefore large numbers of bacilli are seen in dermal macrophages and Schwann cells of the peripheral nerves.

Question 25

The first line of drugs in the treatment of tuberculosis include

1 Pyrazinamide and Rifampin
2 Streptomycin and Cycloserine
3 Ethionamide and Cycloserine
4 Rifampin only
5 Streptomycin only

Answer 25

Pyrazinamide and Rifampin

Effective therapy for infection with Mycobacterium tuberculosis requires use of multiple antimycobacterial agents to avoid the selection of resistant organisms during treatment.
The first line of drugs in the treatment of tuberculosis includes Isoniazid, Rifampin, Pyrazinamide, Ethambutol and Streptomycin.

Question 26

Family Mycobacteriaceae includes genus

1 Mycobacterium and Mycoplasma
2 Mycobacterium and Nocardia
3 Mycobacterium and Rhodococcus
4 Mycobacterium only
5 Mycobacterium and Streptomyces

Answer 26

Mycobacterium only

Mycobacterium is the only genus in the family Mycobacteriaceae.
Mycoplasma belongs to the family Mycoplasmataceae.
Nocardia, Rhodococcus, Streptomyces are aerobic Actinomycetes

Question 27

Mycobacterium leprae differs from all other Mycobacterium in that Mycobacterium leprae:

1 Is negative for acid fast staining
2 Gives positive niacin test
3 Grows only on Löwenstein-Jensen media
4 Grows on Middlebrook agar media within 24 hours
5 Cannot be cultured in vitro

Answer 27

Cannot be cultured in vitro

Mycobacterium leprae cannot be cultured in cell free media. The diagnosis of leprosy is essentially clinically aided by presence of Acid Fast Bacilli in skin lesions and the Lepromin test.

Question 28

The recent advent of antibiotic resistant strains of this organism raise very significant alarm in terms of public health issues. Which of the following organisms has been the cause of serious epidemics for at least several centuries and is often associated with immune-compromised patients?

1 Mycobacterium leprae
2 Mycoplasma hominis
3 Mycobacterium tuberculosis
4 Mycobacterium bovis
5 Mycoplasma pneumoniae

Answer 28

Mycobacterium tuberculosis

Mycobacterium tuberculosis is an ancient pathogen of humankind. It is the causative agent of tuberculosis which is now often associated with AIDS patients from certain risk groups. The recent emergence of antibiotic resistant strains raises the very real danger of a resurgence of epidemic tuberculosis in the western or “developed” nations. Tuberculosis is still a common cause of morbidity and mortality within “underdeveloped” or “emerging” nations today.

Question 29

Actinomyces israelii cause actinomycosis, which is best described as which of the following?

1 Hard, non-tender swelling that develops slowly and eventually drains pus through the sinus tracts
2 A pulmonary infection that progresses to form an abscess
3 Hypopigmented macular skin lesions, thickened superficial nerves, and significant anesthesia of the skin
4 Acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by paroxysmal cough
5 Arthritis due to formation of immune complexes

Answer 29

Hard, non-tender swelling that develops slowly and eventually drains pus through the sinus tracts

Actinomyces israelii cause actinomycosis that is a hard, non-tender swelling that develops slowly and eventually drains pus through the sinus tracts. A pulmonary infection that progresses to form an abscess (nocardiosis) is caused by Nocardia asteroides. Hypopigmented macular skin lesions, thickened superficial nerves, and significant anesthesia of the skin (leprosy) is caused by Mycobacterium leprae. Acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by paroxysmal cough (whooping cough) is caused by Bordetella pertussis. Arthritis due to formation of immune complexes (Lyme disease) is caused by Borrelia burgdorferi.

Question 30

Which bacterial genus is known to be the richest natural source of antibiotics?

1 Penicillium
2 Staphylococcus
3 Streptomyces
4 Haemophilus

Answer 30

Streptomyces

The bacterial genus Streptomyces is the richest source of natural antibiotics known. These organisms are the source of streptomycin, tetracyclines, erythromycin, and chloramphenicol, as well as other antibiotics. These are gram positive, filamentous, or branching bacteria normally found in soil. The mold genus Penicillium is the source of natural penicillin. Staphylococci are normal flora associated with the skin, which can become opportunistic pathogens. Haemophilus species are associated with the nasopharynx and produce respiratory infections.

Question 31

Which one of the following bacteria is part of the normal flora of the oral cavity?

1 Nocardia asteroides
2 Actinomyces israelii
3 Mycobacterium leprae
4 Yersinia pestis
5 Francisella tularensis

Answer 31

Actinomyces israelii

Actinomyces israelii is part of the normal flora of the oral cavity. Nocardia asteroides, Mycobacterium leprae, Yersinia pestis and Francisella tularensis are not part of the normal flora of the oral cavity.

Question 32

In order to confirm a case of tuberculosis and to support your choice of empiric therapy, you must submit a sputum specimen to the laboratory for culture and susceptibility testing of Mycobacterium tuberculosis . It is your expectation that the laboratory in the hospital has the capability to perform all the tests necessary to isolate and identify all species of mycobacteria in order to fully support the management of your patient. If the laboratory can, in fact, perform all of these tests completely, then it must conform to the American Thoracic Society requirements for a laboratory classed as

1 Level I
2 Level II
3 Level III
4 Level IV
5 Level V

Answer 32

Level III

Basically, there are three levels of laboratory service to which a laboratory may subscribe. Level I laboratories are capable of collecting good specimens, transporting these specimens to a higher-level laboratory for isolation and identification, and can prepare and examine smears for microscopic examination. A Level II laboratory performs the functions of a Level I laboratory but has the capability of identifying M. tuberculosis and doing susceptibility tests on this isolate. All other mycobacterial isolates are referred to a Level III laboratory for identification. A level III laboratory serves as a reference laboratory and has the capability of identifying all mycobacterial isolates and doing susceptibility tests as requested.

Question 33

Mycobacteria other than M. tuberculosis (MOTT) are relatively common isolates in the laboratory and may or may not be associated with disease. In fact, some of these isolates may produce pulmonary syndromes indistinguishable from that produced by M. tuberculosis. Which answer correctly describes the recognized Groups of the MOTT?

1 Group I are photochromogens; Group II are scotochromogens; Group III are non-photochromogens; and Group IV are rapid growers
2 Group I are scotochromogens; Group II are photochromogens; Group III are non-photochromogens; and Group IV are rapid growers
3 Group I are photochromogens; Group II are non-photochromogens; Group III are scotochromogens; and Group IV are rapid growers
4 Group I are rapid growers; Group II are photochromogens; Group III are scotochromogens; Group IV are non-photochromogens
5 Group I are scotochromogens; Group II are rapid growers; Group III are photochromogens; Group IV are non-photochromogens

Answer 33

Group I are photochromogens; Group II are scotochromogens; Group III are non-photochromogens; and Group IV are rapid growers

In the late 1950’s, Runyon proposed that the MOTT be divided into four groups based on growth rate and pigmentation. As a result, Group I was designated photochromogens; Group II, scotochromogens; Group III, non-photochromogens; and Group IV, rapid growers. Today, mycobacterial isolates can be placed into one of these groups even though these groups are not taxonomic designations and there are several species within each group. It is preferable to use the correct species name when working with the mycobacteria.

Question 34

A sputum specimen was submitted for a “TB culture” from a patient exhibiting pulmonary symptoms. On the fifth day after submitting the specimen the laboratory telephones to report “acid-fast organisms growing. Identification to follow”. The most likely Mycobacterium species associated with this early report is

1 M. tuberculosis
2 M. kansasii
3 M. gordonae
4 M. avium-intracellulare
5 M. fortuitum

Answer 34

M. fortuitum

Mycobacterium fortuitum belongs to the Group IV (rapid growers) and usually exhibits growth in the laboratory in less than 7 days. The presence of this species does not necessarily imply a pathogenic process, since they may also appear as saprophytes. The other organisms listed may take up to 6 weeks before growth appears in the laboratory, thus they are considered “slow growers”.

Question 35

The specimen of choice for the diagnosis of tuberculosis is usually

1 Saline-induced sputum taken early in the morning
2 A blood culture taken during a fever spike
3 A 24-hour pooled sputum specimen
4 One sputum specimen each morning for three days
5 Gastric lavage after waking up

Answer 35

One sputum specimen each morning for three days

Although several types of specimens may be submitted for culture, sputum is the principal specimen obtained for evaluation. Three to five early morning specimens (5-10 ml) collected on three consecutive days are usually sufficient. Pooled specimens are to be avoided because of increased contamination and lower test sensitivity. Gastric lavage is rarely used but may be necessary on infants or comatose patients. Blood specimens are often not as productive as sputum.

Question 36

A sputum specimen has been collected from a patient at a rural health clinic and the specimen cannot be processed on site. It will take at least 24 hours before the specimen arrives at the reference laboratory for processing. In this case, you need to be assured that Mycobacterium tuberculosis will not be lost during transit. Therefore, what would you recommend that the laboratory use to preserve the specimen during transit?

1 Buffered glycerol saline
2 Cetylpyridinium chloride
3 Stuart’s or Amies transport media
4 Para-dimethylamino-cinnamaldehyde
5 2% NaCl solution

Answer 36

Cetylpyridinium chloride

Cetylpyridinium chloride (CPC) has been proposed for the decontamination, liquefaction, and concentration of sputum specimens that will be in transport for more than 24 hours. An equal volume of a solution of 1% CPC and 2% NaCl is added to the sputum contained in a 50 ml screw-capped centrifuge tube. The tubes are capped and shaken until the sputum appears liquid. The mycobacteria remain viable for 8 days in this solution. No further processing is necessary by the receiving laboratory.
Buffered glycerol saline is used for the transport of some stool specimens while Stuart’s and Amies transport media are components of swab transport systems as well as other types of transport containers but these are not generally useful for mycobacteria. The cinnamaldehyde product is not a transport medium, it is the reagent used in the spot-indole test.

Question 37

In an attempt to culture the etiologic agent of a case of suspected leprosy, a sample of tissue is removed from a characteristic lesion and submitted to the laboratory for culture. The most likely response from the laboratory should be to perform an acid-fast stain and then

1 To inoculate the tissue material to Lowenstein-Jensen medium only
2 To inoculate the tissue material to Lowenstein-Jensen medium, Middlebrook 7H10, and Petragnani media
3 To refuse to culture the tissue because Mycobacterium leprae is a non-cultivable agent in vitro
4 To inoculate the tissue material into a blood culture bottle for automated cultivation
5 To perform an ELISA test on the tissue suspension looking for cell wall antigens

Answer 37

To refuse to culture the tissue because Mycobacterium leprae is a non-cultivable agent in vitro

M. leprae cannot be cultivated in vitro. In fact, the nine-banded armadillo or the foot pads of mice remains the method of choice for cultivation. To date, there are no commercially available direct antigen tests for this organism; although, there are some nucleic acid amplification methods that can detect the presence of this agent in specimens.

Question 38

In addition to a 24-hour turnaround time for the results of a smear for Mycobacterium tuberculosis, which of the following recommendations to the laboratory would seem to best meet the national guidelines of “rapid diagnosis”?

1 Culture on Lowenstein-Jensen medium with biochemical confirmation of typical colonies
2 Culture on an continuously monitored broth-based instrument followed by DNA probes to confirm positive growth
3 Culture of a centrifuged sediment on agar media followed by susceptibility testing on the agent growing on the media
4 An acid-fast or fluorochrome stain of typical colonies taken from agar slants
5 Culture need not be done. Results of the smear are sufficient to confirm a diagnosis

Answer 38

Culture on an continuously monitored broth-based instrument followed by DNA probes to confirm positive growth

Culture for Mycobacterium tuberculosis can take up to 6-8 weeks using conventional laboratory media. Identification of the isolate can take much longer if conventional testing is used. The most rapid means for identifying the etiologic agent of tuberculosis would either be a direct DNA probe of the specimen or the use of a continuously-monitored broth-based instrument such as the BACTEC®, Bac-T-Alert®, or ESP® commercial blood culture instruments. Use of these instruments shortens the incubation period of the “slow-growing” organisms to 7-10 days in some cases. Once the organisms grow in the broth, the instrument indicates a “positive” bottle. That bottle can be removed, the broth centrifuged, stained, and examined by DNA probe testing to arrive at an identification on the same day.

Question 39

Tuberculosis is transmitted from person-to-person primarily by

1 Nebulizers
2 Droplet nuclei
3 Tears
4 Saliva
5 Direct contact

Answer 39

Droplet nuclei

Although M. tuberculosis may enter a susceptible host by several routes, including the skin, genitourinary tract, and alimentary tract, the respiratory tract is by far the most common and important portal of entry. Airborne droplet nuclei of 1-10 μm enter the respiratory tract and are deposited in the alveoli of the lung.

Question 40

During the early stages of tuberculosis, airborne droplet nuclei enter the respiratory tract and are deposited into the alveoli of the lung. The next step in the invasive process of this organism is

1 Enzymatic progression through the alveoli walls into the bloodstream where the immune system first recognizes the antigen
2 Complement activation leading to subsequent inflammatory response
3 Phagocytosis of the bacterial cells with subsequent survival within these cells and dissemination by way of the lymphatics to the lymph nodes
4 Opsonization by the humoral immune system so that the cell-mediated immune response can be initiated
5 Vigorous activation of the cell-mediated immune response to produce a hypersensitive reaction in the lung

Answer 40

Phagocytosis of the bacterial cells with subsequent survival within these cells and dissemination by way of the lymphatics to the lymph nodes

Once the droplet nuclei are deposited in the lung, the bacilli are phagocytized by alveolar macrophages but are still able to multiply both intracellularly and extracellularly. Although a cellular exudative reaction consisting primarily of polymorphonuclear leukocytes ensues, there is actually little host resistance which allows easier dissemination to the lymph nodes. The immune response to infection with this organism is primarily from T-cells.

Question 41

Although primary tuberculosis is of the greatest concern to most physicians, some patients who have been previously infected with Mycobacterium tuberculosis may experience secondary or reactivation disease. The most likely explanation for the reactivation of this disease in patients is

1 There is a local activation of the humoral immune response and a concomitant activation of the complement system that initiates the breakdown of older, calcified lesions in the lung, leading to the reappearance of symptoms
2 Because of the continued exposure of the etiologic agent to long term therapy with multiple antituberculosis drugs, secondary disease emerges when antibiotic resistant strains of M. Tuberculosis reach a critical mass in a dormant lesion and then break through to reinitiate symptoms
3 The influence of pulmonary disease other than tuberculosis, such as bacterial pneumonia, promotes a B-cell response that initiates the breakdown of the calcified lesions in the lung
4 The recrudescence of dormant foci from the primary infection is associated with a local breakdown of the cellular immune system by factors such as age, diabetes mellitus, or obstructive pulmonary disease. Because of the hosts hypersensitivity to the tuberculoprotein, the localized lesion becomes necrotic and undergoes colliquative necrosis
5 The dormant foci throughout the lungs undergo a natural aging process whereby changes in the ultrastructure of the calcified lesion initiate a “leakage” of organisms. Generally, the recrudescence is not influenced by the immune status of the host

Answer 41

The recrudescence of dormant foci from the primary infection is associated with a local breakdown of the cellular immune system by factors such as age, diabetes mellitus, or obstructive pulmonary disease. Because of the hosts hypersensitivity to the tuberculoprotein, the localized lesion becomes necrotic and undergoes colliquative necrosis

Secondary or reactivation disease occurs in people who have been previously infected with M. tuberculosis. It is most commonly caused by recrudescence of dormant foci from the primary infection and is related to a local breakdown in the hosts cellular immune response. Influencing this breakdown are factors such as age, diabetes, obstructive pulmonary disease, and certain other illnesses. A hypersensitive response to the organism’s production of tuberculoprotein causes the local lesion to become necrotic and finally liquefy. If a lesion ruptures into a pulmonary vein, tuberculosis may become disseminated to other parts of the body, a condition known as miliary tuberculosis.

Question 42

Of the following mechanisms of pathogenicity related to pulmonary infection with Mycobacterium tuberculosis, which one is most likely to be the most influential in initiating disease?

1 Toxin production and cord factor
2 Cord factor and intracellular survival in macrophages
3 Plasmid-mediated attachment and intracellular survival in macrophages
4 Enzyme-mediated invasiveness and oxygen-enhanced toxin production
5 Lipid cell wall components and cord factor

Answer 42

Cord factor and intracellular survival in macrophages

Cord factor is a cell surface glycolipid that has received the most attention as a potential virulence factor for the tubercle bacilli. Cord factor is toxic for laboratory animals and plays a major role in the development and persistence of granulomatous lesions of the tubercle bacilli. Clearly, these organisms have the ability to survive intracellularly which is a virulence factor for them.
Toxins are apparently not a pathogenic factor. While the ability to acquire iron from the host and the presence of oxygen tends to correlate to virulence, attachment factors, if present, play a much smaller role.
Enzyme-mediated invasiveness is a mechanism used by the clostridia involved in gas gangrene.
Reference: chapter 171, “Tuberculosis” - page number 1004 in the Fifteenth Edition of Harrison’s under the section titled “etiological agent”

Question 43

Mycobacterium tuberculosis

1 Is acid fast due to very low lipid content of cell wall
2 Is an obligate anaerobe
3 Has cord factor and sulfatide product, which contributes to virulence
4 Cannot survive inside normal macrophage
5 Produces endotoxins

Answer 43

Has cord factor and sulfatide product, which contributes to virulence

Mycobacterium tuberculosis is an obligate aerobe and is acid fact due to very high lipid content. This organism does not produce endotoxins or exotoxins. Virulence factors possessed by the organism enable it to survive in macrophages and form toxic product-like cord factor and sulfatide product.

Question 44

Mycobacteria classified as Runyon group III are

1 Rapid growers and pigmented
2 Slow growers and pigmented
3 Able to produce pigment after exposure to light
4 Able to produce pigment in dark only
5 Slow growers and non pigmented

Answer 44

Slow growers and non pigmented

Runyon classified Mycobacteria into four groups based on their rate of growth and their ability to produce pigments in the presence or absence of light.
Runyon group I - produce pigment after exposure to light.
Runyon group II - produce pigment in dark as well as in the light.
Runyon group III - slow growers and non pigmented.
Runyon group IV - rapid growers and non pigmented.

Question 45

The criteria of positive skin test (PPD) in an immunocompromised patient exposed to
Mycobacterium tuberculosis is

1 Measurement of skin reactivity at 24 hours after intradermal inoculation of 10 μg of PPD
2 Reaction of 10 mm or more induration after intradermal inoculation of 0.1 μg of PPD when measured after 48 hours
3 Reaction of 10 mm or more induration after intradermal inoculation of 10 μg of PPD when measured after 48 hours
4 Measurement of skin reactivity at 72 hours after intradermal inoculation of 5 μg of PPD
5 No reaction after intradermal inoculation of 5 μg of PPD when measured at 48 hours

Answer 45

Reaction of 10 mm or more induration after intradermal inoculation of 0.1 μg of PPD when measured after 48 hours

Criteria for positive skin test in immunocompromised patients, HIV negative drug users, foreign born individuals, and residents of long term care facilities includes the measurement of skin test reactivity at 48 hours after intradermal inoculation of 5 tuberculin units or 0.1 μg of PPD.
Reaction of 10 mm or more is considered positive.

Question 46

Humans are the only natural reservoir for

1 Mycobacterium tuberculosis
2 Mycobacterium bovis
3 Mycobacterium avium
4 Mycobacterium marinum

Answer 46

Mycobacterium tuberculosis

Question 47

Hansen’s disease is caused by

1 Mycobacterium avium-intracellulare
2 Mycobacterium kansasii
3 Mycobacterium ulcerans
4 Mycobacterium leprae
5 Mycobacterium marinum

Answer 47

Mycobacterium leprae

Leprosy is also called Hansen’s disease and is caused by Mycobacterium leprae. Leprosy is spread by person to person contact. The clinical presentation of leprosy is subdivided into tuberculoid leprosy and lepromatous leprosy.
Mycobacterium avium-intracellulare and Mycobacterium kansasii cause localized pulmonary infections and disseminated infections.
Mycobacterium ulcerans and Mycobacterium marinum cause cutaneous disease.

Question 48

Patients with tuberculoid leprosy have

1 Very weak cellular response
2 Strong delayed hypersensitivity reaction
3 Strong humoral antibody response
4 Presence of large number of bacilli in Schwann cells of peripheral nerves
5 Presence of large number of bacilli in dermal macrophages

Answer 48

Strong delayed hypersensitivity reaction

Patients with tuberculoid leprosy have strong delayed hypersensitivity reaction but a weak humoral antibody response. This is characterized by large number of lymphocytes and granulomas and few bacilli are present in tissue because of the production of cytokines mediated macrophage activation, phagocytosis and bacillary clearance.
Patients with lepromatous leprosy have a strong antibody response but weak cellular response to Mycobacterium leprae antigens. Therefore large numbers of bacilli are seen in dermal macrophages and Schwann cells of the peripheral nerves.

Question 49

The first line of drugs in the treatment of tuberculosis includes:

Question 50

The first line of drugs in the treatment of tuberculosis includes:

1 Pyrazinamide and Rifampin
2 Streptomycin and Cycloserine
3 Ethionamide and Cycloserine
4 Rifampin only
5 Streptomycin only

Answer 50

Pyrazinamide and Rifampin

Effective therapy for infection with Mycobacterium tuberculosis requires the use of multiple antimycobacterial agents to avoid the selection of resistant organisms during treatment.
The first line of drugs in the treatment of tuberculosis includes Isoniazid, Rifampin, Pyrazinamide, Ethambutol, and Streptomycin.

Question 51

The family Mycobacteriaceae includes genus

1 Mycobacterium and Mycoplasma
2 Mycobacterium and Nocardia
3 Mycobacterium and Rhodococcus
4 Mycobacterium only
5 Mycobacterium and Streptomyces

Answer 51

Mycobacterium only

Mycobacterium is the only genus in the family Mycobacteriaceae.
Mycoplasma belongs to the family Mycoplasmataceae.
Nocardia, Rhodococcus, and Streptomyces are aerobic Actinomycetes.

Question 52

Mycobacterium leprae differs from all other Mycobacterium in that Mycobacterium leprae

1 Is negative for acid fast staining
2 Gives positive niacin test
3 Grows only on Lowenstein-Jensen media
4 Grows on Middlebrook agar media within 24 hours
5 Cannot be cultured in vitro

Answer 52

Cannot be cultured in vitro

Mycobacterium leprae cannot be cultured in cell free media. The diagnosis of leprosy is essentially clinically aided by the presence of Acid Fast Bacilli in skin lesions and the Lepromin test.

Question 53

Case
A 45-year-old man sees his doctor for follow-up for his medical condition. On physical examination, his liver is palpable and enlarged. There is a bronze hyperpigmentation on his face. His laboratory results are as follows:

TEST RESULTS REFERENCE RANGE
BUN 16 mg/dL 10-20 mg/dL
calcium 9.9 mg/dL 8.5-10.5 mg/dL
potassium 4.2 mEq/L 3.5-5.0 mEq/L
sodium 141 mEq/L 135-145 mEq/L
glucose (fasting) 168 mg/dL 65-110 mg/dL
urine dipstick blood negative negative
urine dipstick glucose positive negative
urine dipstick ketones negative negative
urine dipstick protein negative negative
urine specific gravity 1.029 1.001-1.035
urine pH 6.2 4.5-8.5
He speaks to his doctor because he is concerned that his children may inherit his condition.

How is this most common variant of this disease inherited?

1 Autosomal recessive
2 Autosomal dominant
3 X-linked recessive
4 X-linked dominant
5 Point mutation

Answer 53

Autosomal recessive

This patient has hemochromatosis, or “bronze diabetes”. The “bronze” is due to the skin pigmentation that can occur with hemochromatosis. Hemochromatosis is inherited in an autosomal recessive manner and occurs due to excess iron deposition in tissues; many organs can be involved.
There are 4 types of hemochromatosis. The most common type, type 1, is inherited in an autosomal recessive manner. It is due to a mutation on chromosome 6. The man’s children would only have a chance of being affected if he were to marry someone who has or is a carrier for hemochromatosis.
Autosomal dominant conditions may be passed from parent to child, even if the other parent is not afflicted with the condition.
X-linked recessive and X-linked dominant describes patterns when a genetic disorder is due to a mutation on the X sex chromosome. Because males have only one X chromosome (from the mother), these conditions are more common in boys. Hemochromatosis is not an X-linked condition.
Point mutations are responsible for the random occurrence of genetic disorders. This is no hereditary pattern seen in conditions that are caused by point mutations.