Listeria monocytogenes

Question 1

Physical structure of L. monocytogenes

Answer 1

• G positive rods
• slight hemolysis on blood agar
• acid but no gas from fermentation of carbs.
• facultative psychrophile
• motile at room temp, not at 37C
• facultative intracellular parasite

Question 2

Origin of L. monocytogenes

Answer 2

• native flora in animals

- infection usually following ingestion of infected food(Brie, hot dogs, lunch meat, soft cheese)

Question 3

Clinical presentation of L. monocytogenes

Answer 3

• adult; diarrhea, dysentery, meningitis, bacteremia, myocarditis in immunocomp. and infants
• 2 perinatal versions from infected placenta during 3rd trim.

Question 4

Clinical presentation of L. monocytogenes in infants

Answer 4

• early onset; stillbirth with granulomas

- late onset; type 4b is 2nd most common cause of bacterial meningitis

Question 5

Epidemiology of L. monocytogenes

Answer 5

• mainly a result of contaminated food(unpasteurized)
• result of long term refrigerator of meats and cheese
• queso fresco

Question 6

Pathogenesis of L. monocytogenes

Answer 6

• produce siderophores that bind Fe
• intracellular growth
• membrane protein internalin binds eukaryotic cadherin receptor
• low pH of phagolysosome actives production of listeriolysin O
• bacteria break out of phagolysosome and are surrounded by actin
• bacterial ActA protein causes actin to polymerize and propel Listeria to other cells via filopodia formation
• can move through body without exposure to serum immunity

Question 7

Control of L. monocytogenes

Answer 7

• no vaccine, because intracellular
• ampicillin preferred(or amp + aminoglycoside)
• erythromycin