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Microbiology - Bacteria > Chapter 7: Gram-positive Bacteria: Non-Spore-forming rods: Corynebacterium and Listeria > Flashcards

Chapter 7: Gram-positive Bacteria: Non-Spore-forming rods: Corynebacterium and Listeria Flashcards

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0
Q

Corynebacterium diphtheriae - Gram-stain?

A

Gram-positive

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1
Q

What are the two Gram-positive rods that do not form spores?

A

Corynebacterium diphtheria

Listeria monocytogenes

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2
Q

Corynebacterium - morphology?

A

rods, very pleomorphic and club-shaped, “Chinese-letter” arrangement

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3
Q

Corynebacterium - spore-forming?

A

No spores

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4
Q

Corynebacterium - motility?

A

non-motile

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5
Q

Corynebacterium diphtheriae - metabolism?

A

aerobic (or facultative anaerobic)

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6
Q

Which Gram-positive rods appear very pleomorphic and club-shaped, with random “Chinese-letter” arrangement?

A

Corynebacterium diphtheriae

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7
Q

Corynebacterium diphtheriae - catalase?

A

catalase positive

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8
Q

What special culture requirements are required for detection of Corynebacterium diphtheriae?

A

1) potassium tellurite agar
2) Loeffler’s coagulated blood serum agar

(“TELL yoUR InTErn not to loaf around”)

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9
Q

How does Corynebacterium diphtheria appear when grown on potassium tellurite agar?

A

turns from gray to dark black colonies

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10
Q

How does Corynebacterium diphtheria appear after 12 hours of growth in Loeffler’s medium and stained with methylene blue?

A

metachromatic (red and blue) Babes-Ernst granules

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11
Q

Black colonies on cystine tellurite agar and appearance of rod-shaped pleomorphic bacteria in Loeffler’s coagulated blood serum media is indicative of what microbe?

A

Corynebacterium diphtheriae

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12
Q

How is Corynebacterium diphtheriae transmitted? Where does it colonize?

A

respiratory droplets that colonize the nasopharynx, which serves as a base from where it secretes its toxin

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13
Q

How does infection with Corynebacterium diphtheriae typically present? What if left untreated? (4)

A

1) pseudomembranous pharyngitis (grayish-white membrane)
2) cervical lymphadenopathy (“Bull’s neck”)
3) cranial and peripheral nerve palsy; CNS effects (blurred vision, pharyngeal/diaphragmatic paralysis)
4) arrhythmia and myocarditis

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14
Q

What 2 organ systems are affected in infection with Corynebacterium diphtheriae?

A

1) cardiac (arrhythmia and myocarditis)

2) nervous (peripheral and cranial nerve palsies) (CNS effects: blurry vision and pharyngeal/diaphragmatic paralysis)

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15
Q

Infection with what microbe presents with the following features:

1) pseudomembrane in pharynx
2) cervical lymphadenopathy (“Bull’s neck”)
3) cranial and peripheral nerve palsy; CNS effects (blurred vision, pharyngeal/diaphragmatic paralysis)
4) arrhythmia and myocarditis

A

Corynebacterium diphtheriae

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16
Q

What is the pseudomembrane in oropharynx caused by Corynebacterium diphtheriae infection composed of? (4)

A

fibrin
leukocytes
necrotic epithelial cells
Corynebacterium diphtheriae cells

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17
Q

If you see a dark grayish inflammatory exudate on the pharynx, suggestive of Corynebacterium diphtheriae infection, should you try to scrape it off?

A

No!! It will cause bleeding, and the systemic absorption of the lethal exotoxin will be enhanced.

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20
Q

What is ELEK’s test?

A

Test for presence of Corynebacterium diphtheria toxin.

Have a vertical strip of paper with diphtheria antitoxin (an antibody) just below the surface of agar.
Streak the suspected culture (from a throat swab) perpendicular to the paper strip.
If positive for C. diphtheria, will react with the antibody and form 45deg precipitin lines.

21
Q

How is Corynebacterium diphtheriae diagnosed? (2 requirements)

A

1) Gram-positive rods with metachromatic (blue and red) Babes-Ernst granules - Loeffler’s medium
2) Elek test for presence of toxin

22
Q

What is the treatment for Corynebacterium diphtheriae?

A

1) antitoxin - inactivates circulating toxin which has not yet reached its target tissue, so must be administered quickly to prevent damage to the heart and nervous system
2) penicillin or erythromycin - kills the bacteria to prevent further exotoxin release and render the patient non-contagious
3) DTaP vaccine (7yo)

23
Q

Do all strains of Corynebacterium diphtheriae produce exotoxin? Why or why not?

A

No - Corynebacterium diphtheriae first must by lysogenized by a temperate bacteriophage (beta-prophage)

24
Q

How does Corynebacterium diphtheria exotoxin exert its effects?

A

The AB exotoxin inhibits protein synthesis.
The B subunit binds to cardiac and neural cells and allows the A subunit to enter the cell. Once inside the cell, the A subunit catalyzes the ADP-ribosylation of elongation factor EF2, thereby inhibiting EF2 and preventing tRNA translocation from ribosomal A sites to P sites.

25
Q

Listeria monocytogenes - Gram staining?

A

Gram-positive

26
Q

Listeria monocytogenes - morphology?

A

rods

27
Q

Listeria monocytogenes - motility?

A

motile: has 1-5 flagella (has H-antigen); tumbling motility seen at low temperatures 25deg

28
Q

Which bacterium can be cultured at low temperature (4-10degC) (cold-enrichment) to distinguish it from other bacteria?

A

Listeria monocytogenes - exhibits tumbling motility at 25degC

29
Q

Listeria monocytogenes - spore-forming?

A

no

30
Q

Listeria monocytogenes - metabolism?

A

facultative anaerobe

31
Q

Listeria monocytogenes - catalase?

A

catalase-positive

32
Q

Listeria monocytogenes - hemolysis on blood agar?

A

beta hemolytic

33
Q

What is the only gram-positive microbe with LPS endotoxin?

A

Listeria monocytogenes

34
Q

What virulence factor produced by Listeria monocytogenes is responsible for its beta hemolytic ability on blood agar? Heat stability and antigenicity?

A

Hemolysin

Heat labile / antigenic

35
Q

What 3 groups of patients are at risk of infection with Listeria monocytogenes?

A

1) pregnant women, especially in 3rd trimester
2) neonates
3) elderly and immunocompromised

36
Q

How is Listeria monocytogenes transmitted? (3)

A

1) ingestion of contaminated foods (can survive at low temperatures; unpasteurized dairy products like milk and soft cheeses, deli meats)
2) vaginally (during birth), from asymptomatic mother with vaginal colonization
3) transplacental infection of fetus from bacteremic mother

37
Q

What major virulence factor of Listeria monocytogenes allows it to escape the phagolysosomes of macrophages and avoid intracellular killing?

A

Listerolysin O

38
Q

What is listerolysin O?

A

major virulence factor of Listeria monocytogenes that allows it to escape the phagolysosomes of macrophages and avoid intracellular killing

39
Q

Why are pregnant women (especially in the third trimester), neonates, and the elderly and immunocompromised at high risk of Listeria monocytogenes infection?

A

they are deficient in cell-mediated immunity. Contrast this to in immune competent hosts, where the immune system can release factors that activate the macrophage to destroy intracellular bacteria.

40
Q

Can Listeria monocytogenes survive intracellularly or extracellularly?

A

Both - it is a facultative intracellular organism

41
Q

Why is cell-mediated immunity important to combat Listeria monocytogenes?

A

Listeria monocytogenes can spread from cell to cell, without exposure to antibiotics, complement, and neutrophils.

42
Q

How does Listeria monocytogenes avoid antibody?

A

It forms “rocket tails” (via actin polymerization) that allows it to move through the cytoplasm and into the cell membrane

43
Q

How does Listeria monocytogenes infection present in pregnant women? (3)

A

Amnionitis
Sepsis
Spontaneous abortion

44
Q

How does Listeria monocytogenes infection present in neonates? (2)

A

1) neonatal meningitis (about 2 weeks postpartum when transmitted vaginally during birth)
2) granulomatosis infantisepticum (placental transmission) - early-onset sepsis and formation of granulomas throughout the body, including presence of a rash

45
Q

How does Listeria monocytogenes infection present in the elderly and in immunocompromised patients?

A

meningitis
(is the second most common cause of meningitis after Pneumococcus in people over >50, an most common cause in immunocompromised)

46
Q

How does Listeria monocytogenes infection present in otherwise healthy individuals?

A

mild gastroenteritis

47
Q

What is the treatment for Listeria monocytogenes infection? (2)

A

1) Ampicillin

2) Trimethoprim/sulfamethoxazole

48
Q

What bacterium contaminates foods such as milk and soft cheeses, deli meats?

A

Listeria monocytogenes

Microbiology - Bacteria (15 decks)

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