Prevalence and antibiotic susceptibility of Listeria innocua in seafood from selected markets of Lagos, Nigeria

Listeria is a bacterial genus that is widely distributed in fish and fishery products and is a vehicle for food-borne bacterial infections and intoxications. Listeria innocua, though considered nonpathogenic, is a close relative to L. monocytogenes a known food-borne pathogen. It has been implicated in the transfer of antimicrobial-resistant genes. Therefore, this study investigates the prevalence of Listeria innocua and its antimicrobial susceptibility pattern in seafood found in Badagry, Iyana Ipaja, Liverpool, Makoko and Mushin, Nigeria. A total of 500 samples comprising of fresh and smoked blue whiting, croaker and shrimps were collected aseptically from retail outlets across Lagos. Culture, biochemical and sugar tests were carried out to identify L. innocua. 16S rRNA gene sequencing was conducted to confirm the isolates as L. innocua. The antimicrobial susceptibility testing was determined by the disk diffusion assay. Out of 500 seafood samples analysed, 36 (7.2%) were positive for Listeria innocua. Raw croaker had the highest occurrence of 13.0%. The antimicrobial susceptibility test revealed that all isolates were resistant to ceftazidime and cloxacillin. However, high sensitivities to ofloxacin (83.3%) and erythromycin (72.2%) were exhibited by the isolates. The recovery of these antimicrobial-resistant Listeria innocua strains in the seafood samples analysed warrants the need for suitable control procedures as this could constitute a great risk to public health.