Considerations on the isolation of Listeria monocytogenes and other Listeria spp. in food products.

Listeria monocytogenes, a Gram positive bacillus, is well adapted for survival as a saprophyte in soil and decaying vegetation, but also able to cause serious infections, due to its ability of intracellular multiplication and meningeal and placental dissemination. A total number of 43 Listeria spp. strains isolated from food were investigated. Bacterial identification was performed according to standard methodology, based on: Gram staining affinity, morphology, culture aspects on blood agar (examined in oblique light), catalase test, beta/hemolysis (on sheep blood agar), CAMP test and carbohydrates breakdown, i.e., trehalose, mannitol, mannose, rhamnoze, xylose. Out of the 43 analyzed strains, the biochemical and serological assay evidenced: 10 strains of L.monocytogenes (8 belonging to serotype la and 2 strains to the serotype 4 b), 27 of L. innocua, 2 of L. grayi and 4 of L. welshimeri. L. innoqua was the most frequently identified species. L. monocytogenes strains typing confirms that the serotype la is most commonly found in food and serotype 4b was detected in imported foods. This observation has an epidemiological importance for our country.