Multi-Virulence-Locus Sequence Typing of 4b Listeria monocytogenes isolates obtained from different sources in India over a 10-year period

Listeria monocytogenes is an emerging foodborne pathogen responsible for listeriosis. The incidence of listeriosis has increased during the last 2 decades due to the increase in consumption of ready-to-eat foods and change in food consumption habits. Outbreaks and sporadic cases of listeriosis have been reported in developed countries. These reports have helped determine the safety practices needed to control listeriosis. Although L. monocytogenes has been reported from humans, animals, and a variety of foods in India, limited data exist with respect to prevalence and distribution of L. monocytogenes in the Indian subcontinent. The Indian Listeria Culture Collection Centre in Goa maintains all of the isolates received for subtyping and molecular characterization. Of the listerial isolate collection maintained by this center, three fourths of the isolates are of 4b serotype, while the number of other serotypes is very low. Therefore, we screened L. monocytogenes serotype 4b isolates to determine their relevance to previously defined epidemics and/or outbreaks using multi-virulence-locus sequence typing (MVLST). A total of 25 isolates in serogroup 4b of L. monocytogenes were randomly selected from a repository of 156 L. monocytogenes 4b isolates obtained from different sources in India over a period of 10 years. MVLST sequence types (virulence types, VTs) were compared to known epidemic clones and other known isolates in the L. monocytogenes MVLST database. The 25 isolates were grouped into three clusters. Cluster I comprised 21 isolates including animal (n=9), human (n=4), and food (n=8), which matched Epidemic Clone I (ECI, VT20). Three isolates-two from animal and one from food-formed a cluster while a single animal isolate was placed into two novel VTs (VT98 and VT99), respectively. Based on these findings, it can be inferred that ECI has been isolated from a variety of sources and places and has persisted in India for at least 10 years.