Listeria monocytogenes isolated from raw milk: phenotypic and molecular characterization, pathogenicity testing, and multidrug resistance profiling

Foodborne infections are a worldwide public health emergency that actually impact a variety of disorders. In the current research, a total of 300 samples comprising raw milk (100), milk products (100), and chicken (100) were screened for detection of pathogenic Listeria species by using the USDA method. On conventional biochemical characterization, three isolates were identified as Listeria monocytogenes (from raw milk samples) indicating an overall prevalence of Listeria monocytogenes to the tune of 1%. All other samples comprising milk products and chicken samples (100) showed negativity for the presence of any of the Listeria species. Further, all three isolates were subjected to polymerase chain reaction (PCR) targeting genus-specific (prsA and iap) and species-specific gene (isp) in which all three were turn out positive for both the genes, endorsing their identification as Listeria monocytogenes. All three confirmed Listeria monocytogenes isolates were phenotypically assessed for invitro pathogenicity tests like hemolysis on 7% sheep blood agar, CAMP test, and PI-PLC assay. The results revealed their highly pathogenic nature. Subsequently, all these isolates were also assessed for their virulent nature by PCR, targeting the array of markers including virulence-associated genes viz. hlyA, actA, plcA. The results endorsed pathogenic nature of all isolates showing amplification of all targeted virulence genes. The antibiotic resistance profiling revealed occurrence of multidrugresistant pathogenic L. monocytogenes in foods of animal origin with maximum multiple antibiotic resistance (MAR) index of 0.6 and a minimum MAR index of 0.48 in MDR, which is a matter of concern from public health point of view.