Chapter 7: Gram-positive Bacteria: Non-Spore-forming rods: Corynebacterium and Listeria Flashcards
Corynebacterium diphtheriae - Gram-stain?
Gram-positive
What are the two Gram-positive rods that do not form spores?
Corynebacterium diphtheria
Listeria monocytogenes
Corynebacterium - morphology?
rods, very pleomorphic and club-shaped, “Chinese-letter” arrangement
Corynebacterium - spore-forming?
No spores
Corynebacterium - motility?
non-motile
Corynebacterium diphtheriae - metabolism?
aerobic (or facultative anaerobic)
Which Gram-positive rods appear very pleomorphic and club-shaped, with random “Chinese-letter” arrangement?
Corynebacterium diphtheriae
Corynebacterium diphtheriae - catalase?
catalase positive
What special culture requirements are required for detection of Corynebacterium diphtheriae?
1) potassium tellurite agar
2) Loeffler’s coagulated blood serum agar
(“TELL yoUR InTErn not to loaf around”)
How does Corynebacterium diphtheria appear when grown on potassium tellurite agar?
turns from gray to dark black colonies
How does Corynebacterium diphtheria appear after 12 hours of growth in Loeffler’s medium and stained with methylene blue?
metachromatic (red and blue) Babes-Ernst granules
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?
Corynebacterium diphtheriae
How is Corynebacterium diphtheriae transmitted? Where does it colonize?
respiratory droplets that colonize the nasopharynx, which serves as a base from where it secretes its toxin
How does infection with Corynebacterium diphtheriae typically present? What if left untreated? (4)
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
What 2 organ systems are affected in infection with Corynebacterium diphtheriae?
1) cardiac (arrhythmia and myocarditis)
2) nervous (peripheral and cranial nerve palsies) (CNS effects: blurry vision and pharyngeal/diaphragmatic paralysis)
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
Corynebacterium diphtheriae
What is the pseudomembrane in oropharynx caused by Corynebacterium diphtheriae infection composed of? (4)
fibrin
leukocytes
necrotic epithelial cells
Corynebacterium diphtheriae cells
If you see a dark grayish inflammatory exudate on the pharynx, suggestive of Corynebacterium diphtheriae infection, should you try to scrape it off?
No!! It will cause bleeding, and the systemic absorption of the lethal exotoxin will be enhanced.
What is ELEK’s test?
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.
How is Corynebacterium diphtheriae diagnosed? (2 requirements)
1) Gram-positive rods with metachromatic (blue and red) Babes-Ernst granules - Loeffler’s medium
2) Elek test for presence of toxin
What is the treatment for Corynebacterium diphtheriae?
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)
Do all strains of Corynebacterium diphtheriae produce exotoxin? Why or why not?
No - Corynebacterium diphtheriae first must by lysogenized by a temperate bacteriophage (beta-prophage)
How does Corynebacterium diphtheria exotoxin exert its effects?
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.
Listeria monocytogenes - Gram staining?
Gram-positive
Listeria monocytogenes - morphology?
rods
Listeria monocytogenes - motility?
motile: has 1-5 flagella (has H-antigen); tumbling motility seen at low temperatures 25deg
Which bacterium can be cultured at low temperature (4-10degC) (cold-enrichment) to distinguish it from other bacteria?
Listeria monocytogenes - exhibits tumbling motility at 25degC
Listeria monocytogenes - spore-forming?
no
Listeria monocytogenes - metabolism?
facultative anaerobe
Listeria monocytogenes - catalase?
catalase-positive
Listeria monocytogenes - hemolysis on blood agar?
beta hemolytic
What is the only gram-positive microbe with LPS endotoxin?
Listeria monocytogenes
What virulence factor produced by Listeria monocytogenes is responsible for its beta hemolytic ability on blood agar? Heat stability and antigenicity?
Hemolysin
Heat labile / antigenic
What 3 groups of patients are at risk of infection with Listeria monocytogenes?
1) pregnant women, especially in 3rd trimester
2) neonates
3) elderly and immunocompromised
How is Listeria monocytogenes transmitted? (3)
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
What major virulence factor of Listeria monocytogenes allows it to escape the phagolysosomes of macrophages and avoid intracellular killing?
Listerolysin O
What is listerolysin O?
major virulence factor of Listeria monocytogenes that allows it to escape the phagolysosomes of macrophages and avoid intracellular killing
Why are pregnant women (especially in the third trimester), neonates, and the elderly and immunocompromised at high risk of Listeria monocytogenes infection?
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.
Can Listeria monocytogenes survive intracellularly or extracellularly?
Both - it is a facultative intracellular organism
Why is cell-mediated immunity important to combat Listeria monocytogenes?
Listeria monocytogenes can spread from cell to cell, without exposure to antibiotics, complement, and neutrophils.
How does Listeria monocytogenes avoid antibody?
It forms “rocket tails” (via actin polymerization) that allows it to move through the cytoplasm and into the cell membrane
How does Listeria monocytogenes infection present in pregnant women? (3)
Amnionitis
Sepsis
Spontaneous abortion
How does Listeria monocytogenes infection present in neonates? (2)
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
How does Listeria monocytogenes infection present in the elderly and in immunocompromised patients?
meningitis
(is the second most common cause of meningitis after Pneumococcus in people over >50, an most common cause in immunocompromised)
How does Listeria monocytogenes infection present in otherwise healthy individuals?
mild gastroenteritis
What is the treatment for Listeria monocytogenes infection? (2)
1) Ampicillin
2) Trimethoprim/sulfamethoxazole
What bacterium contaminates foods such as milk and soft cheeses, deli meats?
Listeria monocytogenes
