Assessment of the Microbiological Quality and Antibiotic Susceptibility Profile of Bacterial Pathogens Associated with Spoilt Oranges (Citrus sinensis) and Watermelons (Citrullus lanatus) Sold in Dutse, Northern- Nigeria

Abstract

Fresh fruits such as oranges and watermelons are vital components of the human diet due to their rich nutritional content. However, these fruits can serve as vehicles for pathogenic microorganisms, especially when exposed to unhygienic handling during harvesting and storage. This study was carried out to assess the microbial quality of oranges and watermelons where approximately 10g of spoilt fruit tissue was aseptically excised from each sample using a sterile scalpel. Twenty fruit samples (10 oranges and 10 watermelons) were randomly collected from local vendors. Standard microbiological techniques were employed to enumerate bacterial loads using serial dilution and pour plate methods. Bacterial isolates were identified using Gram staining and biochemical tests, while antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method. The total viable bacterial counts ranged from 1.3 × 10⁴ to 2.15 × 10⁵ CFU/mL. The highest bacterial load was found on orange sample S4 (2.15 × 10⁵ CFU/mL). Both Gram-positive and Gram-negative bacteria were isolated, with Staphylococcus spp., Streptococcus spp., Bacillus spp., Escherichia coli, Pseudomonas spp., and Klebsiella spp. being the predominant organisms. Pseudomonas spp. had the highest occurrence in watermelon samples (33%), while Staphylococcus spp. and Pseudomonas spp. were most prevalent in orange samples (30% each). Antibiotic susceptibility testing revealed multidrug resistance, with E. coli and Klebsiella spp. being resistant to nalidixic acid and sulfamethoxazole, while Staphylococcus spp. was sensitive to vancomycin and novobiocin. These results highlight the need for improved hygiene in fruit handling and point to potential public health risks from consuming contaminated fresh produce.