Prevalence, Virulence Attributes and Molecular Detection of Listeria spp. from Dairy and Animal Clinical Samples in Junagadh, Gujarat, India

Abstract

Aim: The present study aimed to determine the in vitro virulence profiling and prevalence of Listeria spp., particularly Listeria monocytogenes, isolated from milk, dairy products, and animal clinical samples. Study Design: A total of 350 samples comprising raw milk, milk products, and animal clinical samples were collected and analyzed. Place and Duration of Study: The study was conducted at the Department of Veterinary Public Health & Epidemiology, Junagadh, Gujarat, India, over a period of one year from May 2023 to May 2024. Methodology: Samples were subjected to two step enrichment followed by selective plating on PALCAM agar. Presumptive Listeria isolates were identified using standard biochemical tests and sugar fermentation profiles. Pathogenicity and virulence characteristics were assessed using haemolysis on blood agar, the Christie–Atkins–Munch–Petersen (CAMP) test, and phosphatidylinositol-specific phospholipase C (PI-PLC) activity. Molecular characterization of all biochemically confirmed isolates was carried out by PCR. Results: Among the total of 350 samples, 18 (5.14%) were found positive for Listeria spp. Isolates were proved to be L. monocytogenes (3.71%), L. innocua (0.57%), and L. seeligeri (0.85%). Prevalence was found more in raw milk (10%) in comparison with milk products (5%) and clinical samples of animals (2%). L. monocytogenes contamination was found more in cow milk (12%) in comparison with buffalo milk (8%). Among the virulence factors, haemolytic activity has been found in L. monocytogenes in 16 isolates, CAMP test in 13 isolates, while in PI-PLC activity, it was found positive in all L. monocytogenes isolates. By using PCR analysis, all 18 isolates were confirmed to be Listeria spp. by detecting the prs gene, and out of 18 isolates, 13 were amplified for hlyA genes that were confirmed as L. monocytogenes. Conclusion: The predominance of L. monocytogenes in raw milk highlights its significant zoonotic potential and public health risk. The detection of other Listeria species indicates microbial diversity in the dairy ecosystem. These findings emphasize the need for continuous surveillance, strict hygienic practices, and effective food safety interventions to minimize listeriosis risk.