Occurrence and Molecular Characterisation of Listeria Species in Some Fresh-cut Vegetables and Environmental Samples

Listeriosis remains a foodborne disease to be reckoned with courtesy of its high mortality rate among high-risk persons. This study, therefore, examined the occurrence and the phylogenetic relationship of Listeria monocytogenes isolates from different samples. A total of 175 samples (soil, vegetables and water) were analysed using the FDA-BAM for the isolation of Listeria species. Molecular identification of L. monocytogenes was done by coupling PCR to DNA sequencing analysis of Listeria 16S rRNA genes, and the antibiotic susceptibility profile was studied. Analysis yielded 386 bacteria species and Listeria species was recorded at 78.24%. Of these, the pathogen and agent of listeriosis in humans, L. monocytogenes, was recorded at 16.58% and was isolated from all samples analyzed. Other Listeria species identified are L. innocua, L. rocourtiae, L. grayi, L. fleischmannii, and L. species. Significant difference was observed among the population of isolates from vegetables and water samples, and a significant difference was seen among isolates from soil samples at p < .05. Listeria monocytogenes was significantly higher among isolates from water samples at p < .05. Phylogenetic analysis revealed common ancestry among isolates from the different samples analysed. Isolates are suspected to be of lineage I, commonly associated with human clinical cases. All isolates were resistant to ampicillin/cloxacillin and amoxicillin. However, most of the isolates were sensitive to ciprofloxacin at 92.4%. Though not significantly different, resistance among isolates from environmental samples was higher than isolates from fresh cut vegetables. This study established the presence of L. monocytogenes in all samples and a high level of resistance to commonly used antibiotics. Hence, good agricultural practices and a high level of hygiene are required to protect against infection by the pathogen via fresh-cut RTE foods.