Listeria - Morphology, Classification, Habitat, Medically important species

Classification of Listeria

Classification of Listeria is done as follows:

Domain: Bacteria

Phylum: Bacillota

Class: Bacilli

Order: Bacillales

Family: Listeriaceae

Genus: Listeria

Medically important species of Listeria

Other medically important species of the genus Listeria include:

• Listeria aquatica

• Listeria cornellensis

• Listeria flordensis

• Listeria booriae

• Listeria fleischmannii

• Listeria grandensis

• Listeria grayi

• Listeria innocua

• Listeria invanovii

Characteristics of Listeria

The genus Listeria includes bacteria which are intracellular parasites in mammals. It contains 21 known species, among which Listeria monocytogenes is a medically important human pathogen. It causes the food-borne disease listeriosis which has a case-fatality rate of around 20-25%.

L. monocytogenes can differentiate from other species after observation of hemolysis on blood agar and by biochemical tests.

Morphology of Listeria

Morphologically, Listeria spp. is gram-positive, rod-shaped, facultatively anaerobic bacteria that do not produce endospores and occurs in short chains. Flagella are observed at room temperature but not at 37°C.

In direct smears, they may be confused with gram-positive cocci such as streptococci while longer cells may resemble corynebacteria.

Habitat of Listeria

Listeria spp. habitats the soil, stream water, sewage, plants, uncooked meats, uncooked vegetables, pasteurized or unpasteurized milk, and fruits. Although heat kills Listeria, contamination may occur after cooking and before packaging.

Clinical significance of Listeria

Listeria has clinical significance and is the causative agent of a rare and serious disease called listeriosis. It is caused by the consumption of food contaminated by bacteria. Risk groups include pregnant women, newborns, the elderly, immunocompromised, etc.