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

Question 0

Corynebacterium diphtheriae - Gram-stain?

Answer 0

Gram-positive

Question 1

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

Answer 1

Corynebacterium diphtheria

Listeria monocytogenes

Question 2

Corynebacterium - morphology?

Answer 2

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

Question 3

Corynebacterium - spore-forming?

Answer 3

No spores

Question 4

Corynebacterium - motility?

Answer 4

non-motile

Question 5

Corynebacterium diphtheriae - metabolism?

Answer 5

aerobic (or facultative anaerobic)

Question 6

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

Answer 6

Corynebacterium diphtheriae

Question 7

Corynebacterium diphtheriae - catalase?

Answer 7

catalase positive

Question 8

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

Answer 8

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

(“TELL yoUR InTErn not to loaf around”)

Question 9

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

Answer 9

turns from gray to dark black colonies

Question 10

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

Answer 10

metachromatic (red and blue) Babes-Ernst granules

Question 11

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?

Answer 11

Corynebacterium diphtheriae

Question 12

How is Corynebacterium diphtheriae transmitted? Where does it colonize?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

1) cardiac (arrhythmia and myocarditis)

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

Question 15

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

Answer 15

Corynebacterium diphtheriae

Question 16

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

Answer 16

fibrin
leukocytes
necrotic epithelial cells
Corynebacterium diphtheriae cells

Question 17

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

Answer 17

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

Question 20

What is ELEK’s test?

Answer 20

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.

Question 21

How is Corynebacterium diphtheriae diagnosed? (2 requirements)

Answer 21

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

Question 22

What is the treatment for Corynebacterium diphtheriae?

Answer 22

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)

Question 23

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

Answer 23

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

Question 24

How does Corynebacterium diphtheria exotoxin exert its effects?

Answer 24

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.

Question 25

Listeria monocytogenes - Gram staining?

Answer 25

Gram-positive

Question 26

Listeria monocytogenes - morphology?

Answer 26

rods

Question 27

Listeria monocytogenes - motility?

Answer 27

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

Question 28

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

Answer 28

Listeria monocytogenes - exhibits tumbling motility at 25degC

Question 29

Listeria monocytogenes - spore-forming?

Answer 29

no

Question 30

Listeria monocytogenes - metabolism?

Answer 30

facultative anaerobe

Question 31

Listeria monocytogenes - catalase?

Answer 31

catalase-positive

Question 32

Listeria monocytogenes - hemolysis on blood agar?

Answer 32

beta hemolytic

Question 33

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

Answer 33

Listeria monocytogenes

Question 34

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

Answer 34

Hemolysin | Heat labile / antigenic

Question 35

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

Answer 35

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

Question 36

How is Listeria monocytogenes transmitted? (3)

Answer 36

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

Question 37

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

Answer 37

Listerolysin O

Question 38

What is listerolysin O?

Answer 38

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

Question 39

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

Answer 39

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.

Question 40

Can Listeria monocytogenes survive intracellularly or extracellularly?

Answer 40

Both - it is a facultative intracellular organism

Question 41

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

Answer 41

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

Question 42

How does Listeria monocytogenes avoid antibody?

Answer 42

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

Question 43

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

Answer 43

Amnionitis Sepsis Spontaneous abortion

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

How does Listeria monocytogenes infection present in otherwise healthy individuals?

Answer 46

mild gastroenteritis

Question 47

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

Answer 47

1) Ampicillin | 2) Trimethoprim/sulfamethoxazole

Question 48

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

Answer 48

Listeria monocytogenes