Clinical Bacteriology: Gram Positive Bacteria - Other

Question 1

Patient presents with pseudomembranous pharyngitis. Gram positive club-shaped rods with metachromatic (blue and red) granules are found. Additionally, the organism grows black colonies on cysteine-tellurite agar. What is this organism?

The Elek test is positive. What does it test for?

Answer 1

Coronybacterium diphtheriae

Elek test is for diphtheria toxin.

Question 2

What disease is caused by Coronybacterium diphtheriae?

Pathogenesis? Symptoms?

Answer 2

Diphtheria

Diphtheria toxin: An exotoxin, inhibits protein synthesis via ADP-ribosylation of EF-2.

Symptoms: Pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy, myocarditis, and arrhythmias.

Toxoid vaccine prevents diphtheria.

ABCDEFG:

ADP-ribosylation

Beta-prophage

Corynebacterium

Diphtheriae

Elongation Factor 2

Granules

Question 3

What is the purpose of bacterial spores?

What are they made of?

How do you destroy a bacterial spore?

Answer 3

Spores resistant heat, chemicals, and dehydration.

Dipicolinic acid in their core. Keritin-like outer coat. Peptidoglycan.

Kill by autoclave (steam at 121°C for 15 minutes.

Question 4

What are some gram-positive spore-forming bacteria?

Answer 4

Bacillus anthracis, Clostridium perfringens, Clostridium tetani.

Others: Bacillus cereus, Clostridium botulinum, Coxiella burnetii

Question 5

Patient presents with spastic paralysis, trismus, and risus sardonicus.

What bacterial infection are you suspicious for? How does it cause this disease?

Answer 5

*Clostridium tetani, *causing Tetanus

Trismus = lockjaw

Risus sardonicus = spasm of facial muscles, appearance of grinning.

Tetanospasmin exotoxin: Protease that cleave releasing proteins (SNAREs) for inhibitory neurotransmitters (GABA and glycine) from Renshaw cells in the spinal cord.

Tetanus is tetanic paralysis.

Question 6

A patient presents with flaccid paralysis. He admits to ingesting self-canned foods. What organism are you suspicious for? What is the pathogenesis of this disease?

Answer 6

Clostridium botulinum - causing botulism.

Produces a preformed, heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism.

In adults, due to ingestion of preformed toxins

In babies, ingestion of C. botulinum spores in honey causes disease (floppy baby syndrome).

Botulinum is from bad bottles of food and honey.

Question 7

What disease is caused by Clostridium perfringens?

What is the pathogenesis?

Answer 7

Produces α toxin (“lecithinase,” a phospholipase) that can cause myonecrosis (gas gangrene) and hemolysis.

Perfringens perforates a gangrenous leg.

Question 8

Patient presents with pseudomembranous colitis with a history of antibiotic use.

Organism? Pathogenesis? Treatment?

Answer 8

Clostridium difficile.

Produces 2 toxins: Toxin A, enterotoxin, binds brush border of the gut.

Toxin B, cytotoxin, causes cytoskeletal disruption via actin depolymerization -> pseudomembranous colitis -> diarrhea.

Diagnosed by detection of toxins in stool.

Treat with metronidazole or oral vancomycin. For recurrent cases, fecal transplant may prevent relapse.

Question 9

Patient presents with an ulcer with a black center.

Testing discovers a gram-positive rod. What organism are you suspicious for?

What are some of its special characteristics?

Answer 9

Bacillus anthracis, causing cutaneous anthrax.

Cutaneous anthrax: Boil-like lesion -> ulcer with black eschar. Painless and necrotic. Uncommonly progresses to bacteremia and death.

Produces spores

Produces anthrax toxin, AKA Edema Factor: Mimics adenylate cyclase enzyme, increases cAMP, may be responsible for edematous borders of black eschar in cutaneous anthrax.

Only bacterium with a polypeptide capsule (contains D-glutamate)

Question 10

A woolsorter presents with flu-like symptoms that rapidly progresses to fever, pulmonary hemorrhage, mediastinitis, and shock.

Sputum sample reveals gram-positive rods. What organism are you suspicious for?

Answer 10

Bacillus anthracis.

Inhalation of spores causes disease.

Woolsorter’s disease: Inhalation of spores from contaminated wool.

Question 11

Patient presents with nausea and vomiting a few hours after eating at an all-you-can-eat buffett.

Patient confirms a history of eating fried rice.

What organism are you suspicious for? Pathogenesis?

Answer 11

*Bacillus cereus, *causing reheated rice syndrome.

Spore-forming gram positive bacteria. Spores survive cooking rice. Keeping rice warm results in germination of spores and enterotoxin formation.

Toxin - cereulide, a preformed toxin.

Can cause emetic type disease (rice and pasta), nausea/vomiting within 1-5 hours.

Diarrheal type: Watery, nonbloody diarrhea and GI pain within 8-18 hours.

Question 12

What is the appearance of Listeria monocytogenes on microscopy and its characteristic features?

Answer 12

Gram-positive rod that is a facultative intracellular microbe. Use actin polymerization (rocket tails) to move between cells. Characteristic tumbling motility. Only gram positive organism to produce LPS.

Question 13

How is Listeria monocytogenes transmitted?

What diseases does it cause?

How do you treat?

Answer 13

Ingestion of unpasteurized dairy products, deli meats, transplacental transmission, or vaginal transmission.

Causes amnionitis, septicemia, and spontaneous abortion in pregnant women. Granulomatosis infantiseptica, neonatal meningitis, meningitis in immunocompromised patients, mild gastroenteritis in healthy individuals.

Treatment: Gastroenteritis self-limited. Ampicillin in infants, immunocompromised, and the elderly in empirical treatment of meningitis.

Question 14

What are the gram-positive branching filamentous bacteria?

Answer 14

Actinomyces and Nocardia.

Question 15

What are the characteristic features of Actinomyces?

What diseases does it cause?

How do you treat?

Answer 15

Branching filamentous gram-positive bacteria

Anaerobe

Not acid fast

Normal oral flora

Causes oral/facial abscesses that drain through sinus tracts. Forms yellow “sulfur granules”

Treat with penicillin.

Question 16

What are the characteristic features of Nocardia?

What diseases does it cause?

How do you treat?

Answer 16

Branching filamentous gram-positive bacteria

Aerobe

Acid fast (weakly)

Found in soil

Causes pulmonary infections in immunocompromised and cutaneous infections after trauma in immunocompetent

Treat with sulfonamides.

Question 17

Immigrant presents with fever, night sweats, weight loss, and hemoptysis.

Acid-fast organisms are cultured. What is the infection?

Answer 17

Mycobacterium tuberculosis

(or Mycobacterium kansaii - pulmonary TB-like symptoms)

See page 134 for an overview.

Question 18

What are some virulence factors of Mycobacteria?

Answer 18

Cord Factor: Inhibits macrophage maturation and induces release of TNF-alpha. In virulent strains.

Sulfatides (surface glycolipids) - inhibit phagolysosomal function.

Question 19

What does a positive PPD mean?
When can people have a negative PPD but still have tuberculosis?

What is a more specific test for TB?

Answer 19

Positive PPD: Current infection, past exposure, or BCG vaccinated

Negative PPD: Either no infection or anergic (steroids, malnutrition, immunocompromise) and in sarcoidosis.

Interferon-γ release assay (IGRA) more speicfic - fewer positive from BCG vaccination.

Question 20

What are characteristic findings in primary tuberculosis?

Answer 20

Primary TB: Nonimmune host infected with TB.

Ghon complex: Description of enlarged hilar lymph nodes and a Ghon focus usually in the mid zone of the lung.

Ghon focus: A small area of granulomatous inflammation (TB makes caseating granulomas) that can calcify.

Question 21

What are some possible outcomes of primary TB infection?

Answer 21

1. Ghon focus heals by fibrosis, immunity and hypersensitivity to TB develop, tuberculin is positive on PPD.
2. Progressive lung disease (occurs in HIV or malnutrition) -> death
3. Severe bacteremia -> Miliary tuberculosis -> Death
4. Preallergic lymphatic or hematogenous dissemination -> Dormant tubercle bacilli in several organs -> Reactivate during adult life.

Question 22

How does one get secondary TB?

What are characterstic lung lesions in secondary TB?

Answer 22

Secondary TB is due to reinfection in a partilly immune hypersensitized host or by reactivation of latent tuberculosis.

In the lungs, forms fibrocaseous cavitary lesions, usually in the upper lobes.

Question 23

What are some extrapulmonary manifestations of tuberculosis?

Answer 23

CNS: Parenchymal tuberculoma or meningitis

Vertebrae: Pott disease

Lymphadenitis

Renal tuberculosis

GI

Adrenals

Question 24

What is mycobacterium avium-intracellulare?

What kind of disease does it cause?

Treatment?

Answer 24

Acid-fast bacteria that causes disseminated, non-TB disease in AIDS.

Give prophylactic treatment with azithromycin. Tends to be resistant to multiple drugs.

Question 25

Patient presents with “glove and stocking” loss of sensation and lion-like facies.

What organism may cause this disease?

Answer 25

Mycobacterium leprae - Hansen disease.

Acid-fast bacillus, likes cool temperatures, infects skin and superficial nerves.

Question 26

Describe the differences between the two forms of leprosy.

Answer 26

Lepromatous: Presents diffusely over the skin, with leonine (lion-like) facies. Communicable. Characterized by low cell-mediated immunity with a humoral Th₂ response.

Tuberculoid: Limited to a few hypoesthetic hairless skin plaques. Characterized by high cell-mediated immunity with a largely Th₁-type immune response.

Lepromatous can be lethal.

Question 27

What is the treatment for Mycobacterium leprae?

Answer 27

Multidrug therapy consisting of dapsone and rifampin for 6 months for tuberculoid form.

Dapsone, rifampin, and clofazimine for 2-5 years for lepromatous form.