Detection of Listeria monocytogenes from Raw Milk (Nono) in Cows Using Polymerase Chain Reaction

Listeria monocytogenes is an important bacterial pathogen transmitted through milk and dairy products. This study that aimed to detect L. monocytogenes contamination of raw milk using polymerase chain reaction (PCR) is the first PCR-based detection of L. monocytogenes from raw milk in Ogun and Oyo States. Twenty-six bovine milk samples were collected for analysis. L. monocytogenes isolation, molecular identification, antimicrobial susceptibility testing, and plasmid detection were done using standard bacteriological, Kirby-Bauer disc diffusion, and molecular methods, respectively. Eighteen samples were presumptively positive for Listeria species. Of the 18 isolates, molecular analysis of the actA gene confirmed 5/18 (27.8%) as L. monocytogenes. All L. monocytogenes isolates were resistant to erythromycin, cefuroxime, and amoxicillin. Four (80%) and 1 (20%) showed resistance to imipenem and cefepime, respectively. Although all L. monocytogenes isolates were susceptible to ciprofloxacin, all isolates were multidrug resistant. Only 1/5 (20%) isolates possessed plasmid (size, 12.2 kb). While the high milk contamination highlights a potential Listeria outbreak, the high rate of multidrug resistance and plasmid possession observed among L. monocytogenes isolates underscore a serious public health threat due the high chances of disseminating plasmids that mediate antimicrobial resistance to other bacteria and the difficulty in treatment if implicated in infection. However, PCR detection efficiency indicates its effectiveness in enhancing surveillance that could reduce public health impact of listeriosis.