Listeria

Listeria monocytogenes bacterium causes listeriosis, a rare but serious infectious disease.

Characteristics of Listeria

Listeria monocytogenes is a mobile Gram positive bacterium which does not produce spores. The cell is 1 to 4 micrometres long and 0.5 micrometres wide and forms short chains or small clusters.

Its genome is composed of a chromosome containing approximately 3 million base pairs that code 3,000 proteins.

The bacterium can grow in the presence or absence of oxygen (facultative anaerobe) between 1°C and 45°C,. It is relatively resistant to salt and drying and is easily destroyed by heat.

Listeria and listeriosis

These features explain why it can survive for long periods of time in the environment and in animal and human cells and grow slowly at food refrigeration temperatures (4°C). In adittion, it can cross the placenta and enter the central nervous system (meningo-encephalitis).

The virulence genes are coded by a well-defined chromosomal region. Despite listeria being sensitive to most antibiotics which are effective on Gram positive bacteria, the mortality rate is as high as 20 to 30% and leaves neurological complications in 40% of cases.