Occurrence of Listeria monocytogens in raw milk of ruminants

The present study was performed on three hundred raw milk samples, 100 each from cows, sheep and buffaloes were collected from different places of Basrah city. 7.3 % of the samples were found to be positive for Listeria spp. Cow's milk was found to be more infected than other animals milk with this bacteria. All bacterial isolates were confirmed as L. monocytogens by colony characteristics, beta haemolysis, cold enrichment procedure, selective media, Anton test, tumbling and inverted pine tree motility and sugar fermentation tests. Most isolates were found to be sensitive to cefotaxine, sulfamethoxazol, chloramphenical and tobramycin. rifampicin was found to have less effect on these isolates. Effects of pH and temperature on bacterial growth were also studied to test the ability of this microorganism to survive in milk under severe conditions. The pH range for growth was from 4 to 9.5. The temperature range was between 4 – 45 oC.