Occurrence of Listeria Species in Nigerian Street-Prepared Foods and Association with their Environment and Antibiotic Resistance Status

The presence and detection frequency of Listeria species in some Nigerian street-prepared foods were investigated along with association with their sales locations and antibiotic resistance. Multi-stage sampling technique was adopted with towns, street locations (earth/tarred roads, market and Motor Park areas, and dumpsites’ vicinity), and sales points as primary, secondary, and tertiary stages, respectively. The selected popular foods were roasted plantain and yam, akara, and fried fish. Detection and enumeration of Listeria in 192 food samples were undertaken using buffered peptone broth (resuscitation) and Listeria selective medium. Identification was by API system while identities of 3 most frequently detected species were confirmed by molecular methods. Susceptibility of the 3 species to 10 commonly used antibiotics was determined by agar diffusion method. Detected species with frequencies (%) were: L. monocytogenes, 29.6 L. innocua, 23.9; L. grayi 21.8; L. ivanovii 5.7; L. seeligeri 3.6; and L. welshimeri 3.1. The presence of L. monocytogenes and L. grayi in food samples was significantly associated with all locations (X2=5.16- 17.42; P=0.000-0.02) while only Motor Park and dumpsite environments were associated with L. innocua (X2=12.08; P=0.001). The 3 species were MDR and amoxicillin, co-trimoxazol and erythromycin were the commonly resisted antibiotics. MAR index of L. monocytogenes was higher (0.44±0.08 vs 0.40±0.05 and 0.31±0.06; F= 45.03; P=0.003-0.006) than those of L. innocua and L. grayi. The vulnerability of street foods to contamination by L. monocytogenes, the causative agent of listeriosis, was therefore indicated. Health agencies can intervene at sales environment to limit street food contamination by Listeria species.