Prevalence of Listeria species and Growth Potential of Listeria monocytogenes in Typical Nigerian Traditional Street Foods

Aims: Listeriosis is a deadly disease associated with foods contaminated by Listeria species particularly L. monocytogenes (Lm). Listeriosis has been under-reported in Africa especially from consumption of typical street foods. The investigation was therefore directed at determining the presence of Listeria species in typical Nigerian street foods and the potential to support growth of Lm because of the health risk.

Study Design: Laboratory experiments were designed to ascertain Listeria presence and growth in randomly selected street foods (akara, moimoin, suya meat, fried fish, and roasted plantain and yam) from 6 towns across the oil-rich Delta State, Nigeria during wet and dry seasons.

Place and Duration of Study: Department of Microbiology laboratory, Delta State University Abraka, Nigeria was used for the study conducted in July-September, 2023 and January-March, 2024 covering wet and dry season, respectively.

Methodology: Listeria selective medium was used for isolation and enumeration of Listeria species from 180 samples of the street foods after rejuvenation in Buffered Peptone Water. Identification was by microscopic and biochemical tests. The European Union Reference Laboratory guide was used for growth potential tests.

Results: Prevalence of Listeria by towns and food type were 6.6-25.9 and 15.7-22.8%, respectively without significant seasonal differences. Listeria populations significantly differed in the foods (F=5.32-49.20; P=0.000) except in one town. The identified species were: L. monocytogenes, L. innocua, L. ivanovii, L. grayi,L. seeligeri and L. weishmeri with prevalence of 53.9, 15.6, 13.3, 8.9, 4.4 and 3.9%, respectively. Roasted yam and plantain (starchy foods) failed to support growth of Lm (δ=0.20-0.34 log cfu/g) while the other protein-based foods did (δ=0.58-1.58 log cfu/g). Contaminated foods did not support growth of Lm except in fried fish stored in refrigerators (δ=0.59) and suya (δ= 0.52).

Conclusion: Listeria species can be found in typical Nigerian traditional street foods some of which can support the growth of L. monocytogenes with attendant public health implication.