Listeria monocytogenes - Classification, Morphology, Habitat, Transmission, Culture, Biochemical characters

Classification of Listeria monocytogenes

Listeria monocytogenes can be classified as:

Domain: Bacteria

Phylum: Bacillota

Class: Bacilli

Order: Bacillales

Family: Listeriaceae

Genus: Listeria

Species: monocytogenes

Morphology of Listeria monocytogenes

Listeria monocytogenes is an important human pathogen that causes the food-borne disease listeriosis. It is non-capsulated, non-sporing, non-acid fast, growing at 35-37°C; 5-10 % CO₂.

Morphologically, the bacterium is gram-positive, rod-shaped arranged in short chains, measuring about 1-3 X 0.5 µm. It shows tumbling motility with peritrichous flagella at 22-25°C, but not motile at 37°C.

Habitat of Listeria monocytogenes

Habitatwise, Listeria monocytogenes are distributed worldwide. It occurs as a saprophyte in soil, water, and sewage and has been isolated from milk, cheese, and other milk products.

Transmission of Listeria monocytogenes

Listeria monocytogenes are food-borne (esp. milk and milk products). They are transmitted via direct contact with infected animals and animal products, and inhalation while vertical transmission occurs if the mother consumes contaminated food during pregnancy.

Cultural characteristics of Listeria monocytogenes

Listeria monocytogenes can be cultured in ordinary medium but grows better on BA, Typtose phosphate agar.

BA: After 24 hours of incubation, they produce a round, smooth, translucent, non-pigmented colony. It also produces a zone of weak β-hemolysis. Thus, may be confused with group B Streptococci

Biochemical characters of Listeria monocytogenes

Some biochemical characteristics of Listeria monocytogenes are:

• ferments sugars such as glucose, and salicin with acid production

• MR, VP = positive (+ve)

• Oxidase = negative (-ve)

• Urease = negative (-ve)

• Indole = negative (-ve)

• H2S = negative (-ve)