Listeria species in bovine raw milk: A large survey of Central India

Milk samples collected from 2060 dairy cows were examined for the presence of Listeria species. Following enrichment and plating on selective agar, confirmation of the isolates was based on biochemical tests followed by Christie, Atkins, Munch Petersen (CAMP) test, phosphatidylinositol-specific phospholipase C (PI-PLC) assay. The isolates were subjected to PCR assay for the hlyAgene. Listeria spp. were isolated from 139 (6.75%) samples; 105 (5.1%) were positive for L. monocytogenes; 2 (0.1%) for L. seeligeri, 18 (0.9%) for L. innocua and 2 (0.1%) for L. welshimeri. All 105 L. monocytogenes isolates were haemolytic and CAMP positive, however, 90 isolates were found to be positive by the PI-PLC assay and for the hlyA gene. Considering the ubiquitous distribution of L. monocytogenes, it is important to maintain strict hygiene and practice pasteurization of raw milk in order to minimize the risks of human infection.