Listeria monocytogenes

L. monocytogenes sources

Sprouts

Raw milk

Soft cheeses

Cold meats

Smoked seafoods

L. monocytogenes general characteristics

Facultative anaerobe

Intracellular - but can be outside

Short

Gram +

Singly or in short chains

Tumbling motility - peritrichous flagella

L. monocytogenes culture and diagnosis

Tumbling motility

Beta hemolysis on BAP (small zone)

Catalase +

Esculin +

Endotoxin +

Tolerates ref temps (2-4C)

L. monocytogenes Virulence Factors - adhesion

D-galactose residues - adhere to host cell D-galactose receptor

L. monocytogenes Virulence Factors - invasion

Endotoxin

Internalin - INL A and B - attaches to macrophage

Listeriolysin O - lyses phagolysosome

Actin A - polymerizes actin

Phospholipase substance

Catalase - ant-oxidative burst

Superoxide dismutase - anti-oxidative burst

L. monocytogenes life cycle step by step

1. Entry - INL A and B

2. Vacuolar lysis - LLO and P1cA

3. Replication - ActA

4. Actin-based motility - rocket ship

5. Cell to cell spread

6. Vacuolar lysis - or repeat

Most important virulence factor of L. monocytogenes

Iron

L. monocytogenes pathogenesis

Gut → Lymph nodes → Bloodstream → Bacteremia → Sepsis/Septicemia

L. monocytogenes affected organs

Liver

Brain - tropism for nerve tissue

Spleen

Crosses placenta - abortion and neonatal septicemia

L. monocytogenes manifestations in pregnant women

Septicemia

Placental Abscess

Spontaneous abortion

L. monocytogenes infxn in healthy px exposed via food

Incubation - 6-48hrs

Mild, self-limiting gastroenteritis 1-3 days

L. monocytogenes treatment

Ampicillin

Vancomycin

Ciprofloxacin

L. monocytogenes prevention

Avoid ingesting raw milk/vegetables