Prevalence, Antimicrobial Resistance, and Virulence of Listeria monocytogenes in Milk from Rural and Urban Sources in Kamrup, Assam

Aim: The study assessed the prevalence, antimicrobial resistance patterns, and virulence factors of Listeria monocytogenes in milk. Place and Duration: The study was carried out in the College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati, Assam and between March, 2023 and March, 2024. Methodology: A total of 450 milk samples were collected from District Kamrup, Assam (India), comprising 225 samples each from rural dairy farms and urban milk selling points. From 75 rural farms, milk was collected from 3 randomly selected cows per farm. Similarly, pooled milk samples were obtained from 75 urban selling points. A standard reference strain (ATCC®13932™) of Listeria monocytogenes was used as a positive control in the study. Results: The overall prevalence of Listeria spp. was 12.44%, with urban milk selling points showing a higher prevalence (15.55%) compared to rural farms (9.33%). Morphological, biochemical, and staining tests confirmed the isolates as Listeria spp., which demonstrated the ability to ferment rhamnose and mannose but not xylose and mannitol. The isolates exhibited high sensitivity to ciprofloxacin (100%), gentamicin (97.14%), and vancomycin (94.28%) but were resistant to penicillin (77.14%) and tetracycline (74.28%). Virulence factors, including hemolysin production and CAMP test positivity, were detected in 62.5% of the isolates. Pathogenicity testing revealed a higher prevalence of virulent strains in urban milk selling points (62.86%) compared to rural farms (37.14%). Conclusion: Therefore, these findings underline the potential public health risks posed by Listeria monocytogenes in milk and milk products. The study emphasizes the importance of regular surveillance, stringent hygienic practices in milk handling, and judicious use of antimicrobials to mitigate risks associated with Listeria contamination.