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Listeria monocytogenes

Listeria monocytogenes on agar plate

Listeria monocytogenes is a non-fastidious bacterium growing well on commonly used cultivation media. On blood agar it forms small colonies about 1-2 mm in diameter after 24 hours of cultivation. Colonies are β-hemolytic but many strains of L.monocytogenes produce only narrow zones of hemolysis that frequently do not extend much beyond the edge of the colonies. In appearance, they may resemble colonies of Enterococci or some Corynebacteria.

  Listeria monocytogenes is a bacterium commonly found in soil, stream water, sewage, plants, and food. Each bacterium is gram-positive and rod-shaped. Listeria are known to be the bacteria responsible for listeriosis, a rare but potentially lethal food-borne infection: the case fatality rate for those with a severe form of infection may approach 25%. They are incredibly hardy and able to grow in temperatures ranging from 4°C (39°F), the temperature of a refrigerator, to 37°C (99°F), the body's internal temperature. Furthermore, listerosis's deadliness can be partially attributed to the infection's ability to spread to the nervous system and cause meningitis. Finally, Listeria has a particularly high occurrence rate in newborns because of its ability to infect the fetus by penetrating the endothelial layer of the placenta. Vegetables can become contaminated from the soil, and animals can also be carriers. Listeria has been found in uncooked meats, uncooked vegetables, unpasteurized milk, foods made from unpasteurized milk, and processed foods. Listeria is killed by pasteurization and cooking. There is a chance that contamination may occur in ready-to-eat foods such as hot dogs and deli meats because contamination may occur after cooking and before packaging.

Abbreviated from Wikipedia.

COLONY MORPHOLOGY

listeria monocytogenes listeria monocytogenes beta-hemolysis listeria monocytogenes, blood agar listeria monocytogenes on blood agar
listeria monocytogenes listeria monocytogenes listeria monocytogenes listeria monocytogenes
listeria monocytogenes listeria monocytogenes listeria monocytogenes listeria monocytogenes
listeria monocytogenes Listeria ivanovii and Rhodococcus equi Listeria ivanovii beta-hemolysis  
description image
GRAM-POSITIVE RODS
MOTILE
NONSPOREFORMING
CATALASE: POSITIVE
OXIDASE: NEGATIVE
FACULTATIVELY
  ANAEROBIC

BASIC TESTS
FOR IDENTIFICATION

Growth at 4°C+
Motility at 25°C+
Motility at 37°C-
Tumbling motility in a wet mount+
CAMP test reaction
(with S.aureus)
+
β-hemolysis+*
Innate resistance to CEPHALOSPORINS I,II,III+
D-glucose+
VP test+
Methyl red+
Esculin+
Urea-
Gelatin-
Indole-
H2S-
D-xylose-
  
After 24 hours of cultivation is β-hemolysis often only weak, visible after removal of colonies.
sel media
PALCAM agar
Composition
Appearance
LPM agar
Composition
Oxford agar
Composition
Appearance
gram positive rods drawing

ANTIBIOTIC
TREATMENT

Ampicillin(or AMP + GEN)
Penicillin G (+GEN)

ALTERNATIVES

Trimethoprim-Sulfome-thoxazole(TMP-SMX)

POSSIBLE THERAPY (if susceptible)

Tetracycline
Chloamphenicol
Erythromycin

 

list of anntibiotics
ABX Guide
Johns Hopkins ABX Guide
 
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Listeria sp.

Listeria monocytogenes

Listeriosis

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