Advances in Animal and Veterinary Sciences
Prevalence of Listeria Species in Environment and Milk Samples
Sangeetha Mahadevaiah Shantha, Shubha Gopal*
Department of Studies in Microbiology, University of Mysore, Manasagangotri, Mysore – 570 006, Karnataka, India
*Corresponding author: firstname.lastname@example.org
The previous notion that infection by pathogenic Listeria (listeriosis) is not an important health problem in India starts to be revised now, mainly due to changing habits of the production, distribution and storage of food, favoring the multiplication and spread of cold–tolerant bacteria like Listeria. Despite this altering scenario, data on the prevalence of Listeria on the Indian subcontinent are still rather sporadic. We investigated the occurrence of Listeria species in environmental and raw milk samples from Mysore city (moderately hot, semi–arid climate). Environmental samples included cow dung from cowshed, grazing pasture and soil samples from vegetable–cultivation land. Cold enrichment was used to recover Listeria species from raw cow milk (from individual animals) (n=130), cow dung (collected from individual animals) (n=130) and soil (n=100) samples. 10 g sample in case of cowdung and soil and 10mL in case of milk were transferred to 90 mL BHI broth and incubated at 4oC for two weeks. Aliquots from the enriched broth were streaked on Oxford and PALCAM plates, at weekly intervals. Listeria isolates were subjected to phenotypic and genotypic characterization. Phenotypic characterization included standard biochemical tests such as catalase test, motility at 25 °C and 37 °C, acid production from the canonical panel of carbohydrates, nitrate reduction, esculin hydrolysis, methyl red and Voges Proskauer reaction. Genus– and species–specific primers were used for PCR differentiation of the isolates. L. ivanovii was isolated from 1% of the soil samples, L. seeligeri from 0.76% of the cowdung samples and L. innocua from 0.76% of the raw milk samples tested. Strategies to reduce the incidence of Listeria in environment and milk samples should be implemented.
Key Words: Listeria spp., Raw cow milk, Cowdung, soil, L. ivanovii, L. seeligeri, L. innocua