Genetic diversity, virulence and distribution of antimicrobial resistance among L.monocytogenes isolated from milk, beef and bovine farm environment

Document Type : Full paper (Original article)


Department of Veterinary Public Health and Epidemiology, Madras Veterinary College, Chennai- 600 007



Background: Listeria monocytogenes is an opportunistic intracellular foodborne emerging pathogen and is ubiquitous in nature.  The occurrence of L. monocytogenes in animal production units coupled with their presence in milk, faeces, feed, water, sewage and soil is a contributory factor for food borne listeriosis in humans and animals.  Aims: Genotypic characterization and serogrouping of L. monocytogenes recovered from the different types of samples and studying the antimicrobial patterns phenotypically and genotypically.  Methods: Multiplex PCR was used for confirmation of L. monocytogenes and to identify its serogroup, lineage and for detection of virulence markers.  ERIC and RAPD-PCR were used to characterize those isolates and antimicrobial patterns were studied phenotypically by Kirby-Beaur method and genotypically by PCR.  Results: Out of 474 samples (274 milk and 50 each of soil, feed, sewage and beef) screened, ten L. monocytogenes isolates (milk=8, soil=1 and beef=1) were confirmed by PCR targeting hlyA gene and found to belong 1/2a, 3a serogroup and falls under type II lineage.  Virulence potential assessment revealed that all the ten isolates harbored iap gene while the presence of plcA and plcB genes were noticed in seven and eight isolates respectively.  Six isolates from milk were found to group in the same cluster by ERIC and RAPD fingerprinting suggesting that both these methods are efficient molecular typing tools for L. monocytogenes. Genotypic characterization of AMR genes revealed that seven isolates were positive for tetM, five for mefA, four for msrA and one for lnuA genes while none of the isolate shown tetK, ermA, ermB, lnuB genes.  Conclusions: Presence of L. monocytogenes in bovine farm environmentcoupled with virulence markers and multidrug resistance from the study area suggests that there is possible transmission from the environment to humans and animals which needs to be monitored regularly to ensure food safety and well being of animal and humans.


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