Assessment of Quinolone Susceptibility in Salmonella enterica from Beef Sold in Port Harcourt Markets

Abstract

Background: Foodborne diseases are a major public health challenge globally, disproportionately affecting low- and middle-income countries. Salmonella enterica is a leading bacterial cause of gastroenteritis and invasive infections, often transmitted through contaminated animal-derived foods such as beef. The emergence of antimicrobial-resistant Salmonella, particularly quinolone-resistant strains, threatens effective treatment and public health safety. Objective: This study assessed the prevalence, microbial contamination, and quinolone susceptibility profiles of Salmonella enterica isolated from retail beef sold in major markets in Port Harcourt, Nigeria. Methods: In a cross-sectional study conducted between June and August 2025, sixty (60) raw beef samples were randomly collected from five major markets (Rumuigbo, Big Tree, Mile 1, Mile 3, and Mile 4). Samples were analyzed for total heterotrophic counts (THC) and total fecal coliform counts (TFC) using standard plate count techniques. Isolation and identification of Salmonella enterica involved selective culture media, morphological examination, Gram staining, and biochemical characterization. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method on Mueller–Hinton agar with nalidixic acid, ciprofloxacin, and ofloxacin, and results were interpreted according to CLSI guidelines. Results: Salmonella enterica was detected in 33.3% (20/60) of beef samples. THC ranged from 1.5 × 10⁶ to 6.1 × 10⁶ CFU/g, and TFC ranged from 1.5 × 10⁴ to 2.2 × 10⁴ CFU/g, indicating poor hygienic quality. Antimicrobial susceptibility testing revealed that 60% (12/20) of isolates were resistant to at least one quinolone antibiotic, with resistance highest against nalidixic acid (50%), followed by ciprofloxacin (25%) and ofloxacin (20%). Conclusion: The detection of quinolone-resistant Salmonella enterica in retail beef from Port Harcourt markets represents a significant food safety and public health concern, as resistant strains may compromise first-line therapy for severe salmonellosis. These findings highlight the need for improved meat hygiene practices, antimicrobial stewardship in livestock production, and routine surveillance of antimicrobial resistance in foodborne pathogens.