Bacterial and Fungal Diversity, Load Dynamics, and Antibiogram Profiles of Spoilt Fruits Sold at Jimeta Metropolis, Nigeria. A Comparative Post-Harvest and Public Health Study

Abstract

Fruits are essential for human nutrition due to their rich content of vitamins, minerals, fiber, and antioxidants. However, post-harvest losses due to microbial spoilage remain a major challenge in Nigeria, with approximately 20% of annual fruit production lost before reaching consumers. This study investigated the bacterial and fungal diversity, load dynamics, and antifungal susceptibility profiles of spoiled fruits sold at Kasuwan Gwari Market, Yola, Adamawa State, Nigeria. A total of 50 visibly spoiled fruits comprising oranges, avocados, watermelons, pawpaws, and apples (n=10 per fruit type) were aseptically sampled. Fungal and bacterial isolates were obtained using standard microbiological techniques on Potato Dextrose Agar and selective bacterial media, respectively. Fungal and bacterial loads were quantified as CFU/g, and data were analyzed using two-way ANOVA, chi-square tests, and Tukey's HSD post-hoc comparisons (α=0.05). Antifungal susceptibility was determined using the disk diffusion method according to CLSI M44-A2 guidelines. A total of 75 fungal and 88 bacterial isolates were recovered. Aspergillus niger was the most prevalent fungus (48.0%) with the highest mean load (2.58 × 10⁵ CFU/g), while Pseudomonas spp. dominated the bacterial flora (52.0%) with the highest mean load (3.09 × 10⁵ CFU/g). Significant associations were observed between fruit type and microbial occurrence for both fungi (χ²=34.72, p=0.022) and bacteria (χ²=41.58, p=0.003). Pawpaw supported the highest microbial loads for both fungi (1.82 × 10⁵ CFU/g) and bacteria (1.82 × 10⁵ CFU/g), while watermelon exhibited the lowest. Bacterial loads were approximately 34% higher than fungal loads overall (1.46 × 10⁵ vs. 1.09 × 10⁵ CFU/g). All filamentous fungi were resistant to fluconazole, while Fusarium spp. showed reduced susceptibility to itraconazole (14.2 mm) and amphotericin B (15.8 mm). Nystatin remained universally effective (19.0–25.1 mm). The presence of potentially toxigenic fungi (A. flavus 26.0%, F. oxysporum 34.0%) and enteric bacteria (E. coli 40.0%, Salmonella spp. 14.0%) raises significant food safety concerns, with fungal loads in pawpaw and avocado exceeding NAFDAC limits (1.0 × 10⁵ CFU/g). Spoilt fruits at Kasuwan Gwari Market harbor diverse fungal and bacterial populations, including potentially pathogenic and toxigenic species, with microbial loads exceeding regulatory limits. The significant fruit-microbe associations observed underscore the need for fruit-specific post-harvest interventions, improved cold chain infrastructure, and routine microbiological surveillance to reduce post-harvest losses and protect public health.