Microbial Quality and Antimicrobial Resistance Along the Nile Tilapia (Oreochromis niloticus) Value Chain in Kakamega County, Kenya

Abstract

This study evaluated microbiological risks along the Nile tilapia (Oreochromis niloticus) fish value chain in Kakamega County, Kenya, by assessing microbial loads, pathogen prevalence, and antimicrobial resistance to determine food safety and hygiene standards. Significant variations in microbial counts were observed along the chain, with the highest total plate count (TPC) (8.73 ± 2.06 log10 CFU/g) and total coliform count (TCC) (7.91 ± 1.97 log10 CFU/g) recorded at the wholesale stage, suggesting that postharvest handling practices contribute to increased contamination. In contrast, processing methods such as drying and frying reduced these counts significantly, with values of 4.12 ± 0.97 and 4.39 ± 1.05 log10 CFU/g, respectively. All water samples and contact surface swabs tested positive for coliforms, with levels ranging from 4.96 ± 1.29 to 6.77 ± 1.94 log10 CFU/100 mL for water samples and 4.63 ± 3.32 to 3.69 ± 1.93 log10 CFU/cm2 for contact surfaces, thereby exceeding the World Health Organization (WHO) guidelines and indicating poor water quality and inadequate sanitation management. Among the pathogens, Staphylococcus aureus was most prevalent in fish (94.4%) and water (71.2%), followed by Pseudomonas spp. (65.6% and 45.6%) and Escherichia coli (64.8% and 60%). High contamination at farm level, evidenced by a 93% prevalence of S. aureus in fish, suggests that unhygienic harvesting practices are a primary source of contamination. Moreover, antimicrobial susceptibility testing revealed high resistance to ampicillin (75%) and erythromycin (58%), with multidrug resistance among key isolates. Overall, these findings underscore the urgent need for enhanced hygiene practices, improved water quality management, stricter antimicrobial policies to safeguard public health, and ensure the safety of tilapia fish products.