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

Abstract

<i>Listeria monocytogenes</i> is an important bacterial pathogen transmitted through milk and dairy products. This study that aimed to detect <i>L. monocytogenes</i> contamination of raw milk using polymerase chain reaction (PCR) is the first PCR-based detection of <i>L. monocytogenes</i> from raw milk in Ogun and Oyo States. Twenty-six bovine milk samples were collected for analysis. <i>L. monocytogenes</i> 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 <i>Listeria</i> species. Of the 18 isolates, molecular analysis of the <i>actA</i> gene confirmed 5/18 (27.8%) as <i>L. monocytogenes.</i> All <i>L. monocytogenes</i> isolates were resistant to erythromycin, cefuroxime, and amoxicillin. Four (80%) and 1 (20%) showed resistance to imipenem and cefepime, respectively. Although all <i>L. monocytogenes</i> 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 <i>Listeria</i> outbreak, the high rate of multidrug resistance and plasmid possession observed among <i>L. monocytogenes</i> 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.