Genus Listeria. L.Monocytogenes Flashcards
Classification
Family: Listeriaceae
Genus: Listeria
7 species
Pathogenic :
L.Monocytogenes -> human and animal pathogen
L.Ivanovii -> animal pathogen
L.monocytogenes:
Colonies the GIT and female genital tracts
transmission by ingestion of contaminated cheese, milk …
- across placenta or by contact during delivery
Morphology
Small gram (+) rods
Tumbling motility:
> non-motile at 37oC
> motile at 30oC -> peritrichous flagella
Growth characteristics
Facultatively anaerobic
Fastidious (grow on enriched media)
Resistant to cold temperatures (survives and multiplied in them)
Tolerate high salt concentration (10 - 12% NaCl)
Survives at pH 4.4 to 9.6
> beta hemolytic
Antigenic structure
O antigen -> denoted by I, II, III
H antigen -> denoted by A, B, and C
Serotype 4b causes most of the food borne outbreaks
Virulence factors
Surface components:
- Adhesins: facilitate binding to host cells
- internalins A and B: promote phagocytosis
- ActA: induces host cell actin polymerization
Exotoxins
- Listeriolysin O: loses cell membrane of phagolysosome allowing it to escape into the cytoplasm of the host epithelial cell
Iron
Listeria produce siderophores and are able to obtain iron from transferrin
Diseases
Neonatal listeriosis:
- neonatal meningitis
- sepsis
Adult listeriosis: normally immunocompromised and old adults
- mengingoencephalitis
- Bacteremia
- gastroenteritis
Microbiological diagnosis
DME:
Gram stained smear: small, Gram-positive rods diphtheroids
Culture:
BAP: Small grey colonies with a narrow zone of B-hemolysis
Specific test
In semisolid agar: “umbrella” type of motility at 22oC incubation
Tumbling motility
Serologic tests not useful
Treatment and prevention
Penicillin
Ampicillin + gentamicin -> for severe disease
TMP/SMX: for CNS infections in penicillin allergic patients
Prevention:
Pregnant women and immunocompromised patients should not ingest unpasteurized milk products or raw vegetables
No vaccine available
