Characterization and Antimicrobial Susceptibility Patterns of Listeria monocytogenes from Raw Cow Milk in the Southern Part of Ethiopia

Abstract

Food safety remains the main health concern in the developing countries. Thus, the major purpose of the present study was to characterize and determine antibiotic susceptibility patterns of Listeria monocytogenes from raw milk samples collected from southern Ethiopia. Two hundred and forty raw cow milk samples were collected from dairy farms and smallholder dairy producers using a simple random sampling technique and analyzed by cultural and multiplex PCR methods. The antimicrobial susceptibility profile of L. monocytogenes was evaluated using the standard disk diffusion method. Over 28% of the samples were found positive for Listeria spp., of which 17 (7.08%) isolates were identified as L. monocytogenes after morphological and biochemical confirmation. The prevalence of L. monocytogenes was 6.02% in Hawassa city, 5.56% in Dale district, and 9.41% in Arsi Negele district. L. monocytogenes was higher in the wet season (9.32%) than in the dry season (4.92%). The gene for Listeria specific 16S rRNA was detected in all the 17 examined isolates, while hlyA and iapA were only found in 11 of them. Furthermore, no isolate was identified to have the prfA, actA, or plcA genes. Antimicrobial resistance profiling revealed that all the L. monocytogenes isolates were resistant to nalidixic acid (100%), followed by erythromycin (88.24%). However, all the L. monocytogenes isolates were sensitive to vancomycin, gentamicin, and sulfamethoxazole. Raw cow milk is a potential source of L. monocytogenes and it poses a threat to human and animal health. Therefore, it is crucial that dairy producers and vendors of raw milk in the study areas should take considerable precautions to prevent Listeria species from contaminating raw fresh milk.