Prevalence of Listeria monocytogenes in Foods of Animal Origin: Study from Assam, A North-Eastern State of India

Abstract

Listeriosis is an important emerging bacterial food-borne zoonotic disease caused by Listeria monocytogenes.  During the last two decades, the organism has been implicated in several food-borne disease outbreaks making it a serious public health hazard. The pathogenic strains of Listeria can cause severe illness in man after the ingestion of contaminated food products, especially the refrigerated foods of animal origin. In India, very few studies have been carried out in respect to the occurrence and incidence of L. monocytogenes. Assam, one of the eight states of Northeastern India, where approximately 79.0 percent of the total population are non-vegetarians. Chicken meat, pork, chevon and beef are exclusively taken as regular food items throughout the state. The present study describes about isolation, identification and molecular characterization of L.monocytogens from different foods of animal origin from Assam, India. A total of 750 different meat (chicken, chevon, pork and beef) and milk and their products (curd and paneer) samples were collected and analyzed for presence of Listeria. Isolation of L. monocytogenes was done from different food samples of animal origin by using selective enrichment method. PCR was employed for confirmation of the suspected cultures of Listeria targeting prsand16SrRNAgene. Upon confirmation, the isolates were further characterized based on 16S rRNA gene and phylogenetic analysis was performed. Of 750 samples, 48 (6.4%) samples were found positive. The highest rate of isolation of Listeria spp. was recorded in raw milk (8.95%) followed by curd (6.58%), chevon (5.36%), chicken (5.74%), pork (5.98%) and beef (3.75%).  Molecular characterization of the isolates based on 16S rRNA gene of L.monocytogens isolated from foods of animal origin from Assam with that of other sequences reported from different parts of the world revealed that all the isolates of the present study are clustered along with other L.monocytogens isolates reported from different parts of the world, however, showing more closely related to isolates reported from China.