Flashcards in Acid-Fast Bacilli and Filamentous Bacteria Deck (82):
What are Koch's Postulates?
1. The microorganism must be present in all cases of the disease
2. The pathogen can be isolated and grown in pure culture
3. The pathogen can be inoculated into a healthy, susceptible host and cause disease
4. The pathogen can be reisolated from the new host and shown to be the same as the original inoculated pathogen
What is unique about the growth of mycobacteria and filamentous bacteria?
They are extremely slow growing and resemble fungi on plates
What is the oxygen dependence of mycobacterium?
They are aerobic
What is the generation time for mycobacterium?
Over 24 hours (extremely slow growing)
E. coli generates in 20 minutes
Do mycobacterium more closely resemble gram positive or gram negative bacteria?
Gram positive because they lack LPS (however, they do NOT gram stain)
What is the waxy coat of mycobacterium made of?
What are the layers of the mycobacterial cell wall?
1. cell membrane
4. mycolic acid
5. superficial lipids (cord factor)
6. stretching from cell membrane to cell surface = LAM
What is LAM?
Lipoarabinomannan which is a glycolipid found in numerous subspecies of mycobacteria.
It is a virulence factor that modulates macrophage function and scavenges oxygen radicals
What is the major virulence factor of mycobacteria and how does it work?
LAM modulates macrophage function and scavenges oxygen radicals
What makes mycobacteria waxy, and difficult to stain via gram stain?
Mycolic acids which are very long chain fatty acids. They are in mycobacteria, nocardia and corynebacteria
What three bacterial species have mycolic acids?
What is Wax D?
it is mycolic acid, peptidoglycan and arabinogalactan (the layers of the mycobacterial cell wall below the superficial lipids)
What pathogenesis is associated with Wax D?
1. granuloma formation
2. caseous necrosis
What is Freund's adjuvant?
It is mineral oil and killed Mycobacteria bovis which can be used as an immunopotentiator (booster)
Killed M bovis serves as an antigen to stimulate and immune response and make Ab
What is trehalose dimycolate?
Cord factor associated with mycobacteria.
It forms serpentine cords in culture and is toxic to PMN, damages mitochondria and causes granuloma formation
What is cord factor?
Trehalose dimycolate of mycobacteria
What three pathogenic responses are associated with cord factor?
1. granuloma formation
2. PMN toxicity
3. Damaged mitochondria
Acid fastness is a property of what two bacteria?
Mycobacteria and nocardia
Describe the process of acid-fast staining.,
1. boiling carbol fuschin (red basic dye)
2. acid wash with alcohol and hydrochloric acid
3. Methylene blue counter stain
What is the original stain used in acid-fast staining? Why must it be boiling?
Boiling carbol fuschin (basic red dye) is used. It must be boiling to penetrate the waxy layer
How many species of mycobacterium tuberculosis exist? Which causes most disease in humans?
1. M. tuberculosis
2. M. bovis (disease with ingestion of raw dairy, BCG vaccine)
3. M. africanum
4. M. canetti
5. M. microti
Which mycobacteria tuberculosis species is the basis for the BCG vaccine against TB?
How else is this bacteria acquired?
It can also be acquired by ingesting raw dairy
What percent of the world's population is a reservoir for M. tuberculosis?
How does transmission of M. tuberculosis occur?
person-to-person (inhalation, ingestion), although they can survive on inanimate objects that are out of direct light
Inhalation- 1 to 5 micron droplets that go to alveoli
Ingestion- raw dairy from infected cattle
When M. tuberculosis is in a host, what happens?
1. it gets ingested by macrophages and inhibits phagolysosomal fusion so it is not killed by inactivated macrophages
2. Drain to hilar and mediastinal nodes and multiply locally
3. bacteremic spread to other organs
Why is M. tuberculosis not killed when it is ingested by macrophages?
It prevents the fusion of the phagolysosome so it is able to survive in the inactivated macrophage
What two factors does control of initial M. tuberculosis infection depend on?
1. inoculum size (number of organisms)
2. Resistance of the host (IL-12, IFNg, TNF, immunosuppression HIV, malnutrition)
Resistance of the host to M. tuberculosis can be affected by genetics or acquired factors. What three genetic factors play the largest role in resistance?
IL-12. IFNg, TNF
What are the two types of TB lesions?
1. Exudative- acute, edema, PMN, macrophages
2. Granulomatous- later, central zone with giant cells, midzone epithelioid cells, outer fibroblasts, monocytes, lymphocytes
What are the three zones of granulomatous TB lesions?
central zone- giant cells
midzone- epithelioid cells
Outer zone - fibroblasts, monocytes, lymphocytes
What are the three phases of TB disease?
1. Primary disease
2. Progressive primary disease (or Latent)
3. Reactivation disease
Describe primary disease of TB.
Most are asymptomatic or have mild respiratory infection that may present as pneumonia
Describe progressive primary disease of TB.
This occurs in elderly and immunocompromised and is a progressive pneumonia
What is reactivation disease of TB?
How long does it take for reactivation symptoms to develop?
Where does reactivation most frequently occur?
4% per year in the first two years of the infection get reactivated pneumonia along with:
fever, night sweats, malaise, fatigue and weight loss
It takes months for symptoms to develop and they usually occur at the apices of the lungs because it requires high O2 tension
What are the 5 ways to test for TB?
1. skin testing - PPD, Tuberculin
3. Staining (acid-fast)
5. Molucular techniques (PCR, molecular probes)
What is the "gold standard" of TB testing?
culturing the bacteria
What is the Quantiferon test?
It is a TB test that uses IFNg release assays
Describe the treatment requirements for TB.
They require multiple drugs over extended time
Typical = 4 drugs for 2 months, 2 drugs for 4 months
What does it mean if a TB strain is MDR?
Multi-drug resistant meaning that it is not treated by 2 of the first line drugs
What does it mean if TB is XDR?
extremely drug resistant meaning that it is resistant to the first line drugs (isoniazid, rifampin, fluoroquinolone) and resistnat to at least one second line drug (kanamycin, amikacin, capreomycin)
Non-tuberculosis mycobacteria are also called ______________. They are organized with the _______________ classification system.
They are classified by the Runyon Classification
What are the 4 Runyon Classification groups for atypical mycobacteria?
Which are slow-growing?
1- photochromogens- produce pigment in light
2. Scotochromogens- make pigment in light or dark
3. nonchromogens- no pigment
4. rapid growers
Groups 1,2,3 are slow growing
What are the three group 1 mycobacteria?
Theses are the photochromogens that make pigment in the light.
M. Kansaii- TB-like syndrome
M. Marinum- skin/soft tissue infection with water
M. ulcerans- buruli ulcer from water/soil organism
What is the pigment characteristics of group 2 atypical mycobacteria?
What is an example of this bacteria?
What is the pathogenesis?
Scotochromogens= pigment in light or dark
M. scrofulaceum causes cervical adenitis in kids
What are examples of group 4 mycobacteria? How do they differ from the other mycobacteria?
What pathogenesis do they cause?
They are rapid growers
They usually are just contaminants in culture but occassionally cause infection when a foreign object is left post surgery
What is group 3 Runyon's mycobacteria?
What are the two strains, and which causes most disease in human
They do not produce pigment and are:
M. avium - most infections in humans
What is the environment of type 3 mycobacteria?
ubiquitous in water at a temperature of 41 degrees celcius (like campylobacter)
What are the two major disease syndromes of M. Avium (type 3 runyons)
1. lung disease- usually in patients with preexisting lung disease (smokers, COPD)
2. HIV infections- causes nonfocal fever in patients with HIV and CD4 below 100
M. avium causes nonfocal fever syndrome in patients that have ____________ and a CD4 count below _________.
HIV, below 100
What percent of adults have tattoos?
What mycobacteria is associated with bad tattoo ink?
M. chelonae a type 4 rapid-grower
M. Leprae is associated with what disease?
Hansen's disease (leprosy)
How many cases of leprosy are noted worldwide? In the US?
10 million worldwide
100 in the US
M. leprae is morphologically identical to what other bacteria?
M. leprae cannot be cultured in vitro but must be grown on what?
The footpads of mice and 9 banded armadillos
How is M. leprae spread?
Respiratory or direct contact but transmission is difficult
What is the incubation time of M. leprae?
What are the two classification systems of M. leprae?
1. WHO by number of bacteria (paucibacillary or multibacillary)
2. Ridley-Jopling- lepromatous to tuberculoid
What are the 4 associations of tuberculoid M. leprae?
stronger T-cell response
fewer skin lesions
localized skin reaction
few bacteria (paucibacillary)
What are the 4 associations of lepromatous M. leprae?
1. weak/no T cell response
2. nodular lesions
3. abundant bacteria (multibacillary)
4. progressive clinical course
How do you diagnose M. leprae?
1. acid-fast staining
What is the mainstay treatment of M. leprae?
(rifampin and clofazimine too)
How do nocardia stain with a gram stain?
What is the oxygen consumption of nocardia?
Aerobic- has catalase and SOD
Describe the shape of nocardia.
Filamentous bacteria that has a branching morphology like fungus
What is the minimum number of days needed to culture and grow nocardia?
What bacteria is classified as "weakly acid fast"?
Why is it only weakly acid fast?
Nocardia is weakly acid fast because instead of very long chain mycolic acid lipids, they have short mycolic acid
Where are nocardia found?
In soil- an opportunistic infection
What nocardia strain is in the US and who does it infect?
N. asteroides and it infects immunocompromised patients
What are the 3 clinical syndromes associated with nocardia?
1. subacute pneumonia
2. brain dissemination
3. Skin disease
What is the mode of transmission if someone gets skin disease from nocardia?
What is the strain?
Direct implantation (skin trauma) usually in the tropics
Nocardia Brasiliensis which usually forms granules
What is the drug of choice for nocardia infections?
How long should it be given?
Trimethoprim-sulfamethoxazole given for 6 to 12 months
Describe the structure of Actinomyces.
They are "ray-fungi" that are filamentous branching gram positive rods
They do NOT stain with acid fast
How do you stain actinomyces?
with gram stain.
They do NOT stain with acid fast because they lack mycolic acid
What is the oxygen consumption of actinomyces?
microaerophiles or anaerobic
How long does it take for actinomyces to grow?
Over 2 weeks
What actinomyces strain is the primary human pathogen?
Where are actinomyces found?
Part of normal flora (mouth, GI, GU)
Who does actinomyces infect?
Immunocompromised patients typically following trauma or procedures where foreign objects are introduced
Actinomyces present with chronic __________ noted by the presence of _________ granules.
Chronic draining sinuses associated with sulfur granules
What are the 3 syndromes associated with actinomyces?
1. orocervicofacial- lumpy jaw and bad dentition
2. thoracic- descending infection
3. Abdominopelvic- after surgery