LISTERIA

10 plus species including:

SPECIES

Listeria denitrificans
Listeria grayi
Listeria innocua
Listeria ivanovii
Listeria monocytogenes
Listeria murrayi
Listeria seeligeri
Listeria welshimeri

MICROSCOPIC APPEARANCE

Gram Stain: Positive. Not acid-fast.
Morphology: Regular and short rods or coccobacilli. Commonly found with rounded ends occurring singly or in short chains. When older, long filaments are occasionally formed.
Size: 0.4-0.5 micrometers by 0.5-2.0 micrometers.
Motility: Motility occurs at 25 degrees C by means of one to five peritrichous flagella; apparently always non-motile at 37 degrees C.
Capsules: None.
Spores: None.

MACROSCOPIC APPEARANCE

Colonies have a low-convex profile on nutrient agar. Colonies appear bluish-gray by normal illumination and a blue-green sheen appears under oblique illumination.

KEY BIOCHEMICAL REACTIONS

METABOLIC PROPERTIES

Aerobic and facultatively anaerobic; Chemoorganotrophic. Sugars are fermented with acid produced, not gas. Esculin is hydrolyzed and growth occurs in up to 10-20% sodium chloride.

HABITAT

Bacteria of the genus Listeria are widely distributed in nature and have been isolated from soil, vegetation, sewage, water, animal feed, fresh and frozen poultry, slaughter-house waste and healthy human and animal carriers.

PATHOGENICITY

Listeria monocytogenes is pathogenic for man and a large number of animal species. The occurrence of infections in man is sporadic although a few epidemics have been reported notably in Germany. In man, meningeal involvement sometimes accompanied by septicemia is usually the clinical manifestation. The members of the population most at risk are neonates, the old and those compromised by pregnancy or an underlying illness such as malignancy or alcoholism or some condition which requires immunosuppressive procedures. Intrauterine infection of the fetus results in death, or an acutely ill infant with a septic disseminated form of listeriosis. Papular lesions of the skin may be found in listeriosis of the newborn. A similar cutaneous form has been reported in veterinarians working with infected animals.

RECOMMENDED MEDIA

For culture: Brain Heart Infusion (BHI) Agar.
For selective isolation: Tryptic Soy Agar with 5 % Sheep Blood.
For maintenance: Tryptic Soy Agar, Brain Heart Infusion Agar. Brucella with 20% Glycerol may be used for storage at -70 degrees C. Lyophilization is required for preservation.

INCUBATION

Temperature: 30-37 degrees C.
Time: Up to 48 hours.
Atmosphere: Aerobic and facultatively anaerobic.

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology, Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.

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