Epidemiology and antibiogram of listeria species from retail raw frozen atlantic mackerel fish (Scomber scombrus) in Nigeria

This study was undertaken to determine the epidemiology and antibiogram of Listeria species isolated from raw frozen Atlantic Mackerel (Scomber  Scombrus) fish sold in Enugu State Southeastern Nigeria. Twentyfive grams each of raw fish gut and skin were collected from 800 raw fish sold in 8 major  markets randomly selected from the study area. Isolation of Listeria was done using half and full fraser broths, and polymyxin acriflavine lithium chloride  ceftazidime aesculin mannitol (PALCAM) agar. Confirmation of the genus Listeria was done by a polymerase chain reaction. Identification of species was  done using an analytic profile index (API) kit specific for Listeria. The antibiotic resistance of the isolates was determined using disc diffusion method. Out  of the 800 fish samples, 38 (4.75%) were positive for Listeria species. Enugu North (6.50%) had significantly (P<0.05) higher prevalence than Enugu  East (3.0%). Five Listeria species were identified. Listeria innocua (71.1%) predominated, followed by Listeria welshimeri (10.5%), Listeria ivanovii (7.9%),  Listeria grayi (5.3%) and Listeria monocytogenes (5.3%). All the isolates were susceptible to the tested antibacterial agents. The occurrence of Listeria  species in raw frozen Atlantic mackerel fish, poses a threat, when consumed raw or lightly cooked, to people especially the immunocomprormised persons whose population is increasing as a result of improvement in medical technology. Also, the possibility of cross contamination in the kitchen or  food service establishments is also a concern. Since all the Listeria species got in this study showed 100% susceptibility to all the antimicrobials tested,  therefore, there is no fear of acquiring and transferring antibiotic resistance genes from raw frozen Atlantic mackerel fish to the general human    population.