Microbiological Quality and Phenotypic Quinolone Resistance of Salmonella enterica in Retail Cow Intestines in Port Harcourt Markets, Nigeria

Abstract

Background: The intestinal tract of food animals is a major reservoir of enteric bacterial pathogens, including Salmonella enterica, with implications for food safety and public health. Objectives: This study investigated the microbiological quality, prevalence, and phenotypic quinolone and fluoroquinolone resistance of S. enterica isolated from cow intestines sold in selected markets in Port Harcourt, Nigeria. Methods: A total of 192 cow intestine samples were collected from twelve major markets and analyzed for total heterotrophic bacterial counts (THBC) using standard microbiological techniques. Isolation and identification of S. enterica were performed using conventional cultural and biochemical methods. Antimicrobial susceptibility testing was conducted via the Kirby–Bauer disk diffusion method against Ciprofloxacin, Levofloxacin, Ofloxacin, and Nalidixic acid, following CLSI guidelines. Results: THBC values varied significantly among markets (ANOVA, p < 0.05), with several markets recording markedly high microbial loads. S. enterica was detected in all markets, with prevalence ranging from 87.5% to 100%. Antimicrobial susceptibility testing revealed high resistance to Nalidixic acid (68.1%), whereas most isolates remained susceptible to fluoroquinolones, including Ciprofloxacin (92.6%), Levofloxacin (88.2%), and Ofloxacin (85.6%). This pattern suggests early phenotypic quinolone resistance, where Nalidixic acid resistance may precede clinically apparent fluoroquinolone resistance. Conclusion: The findings highlight widespread contamination of cow intestines with S. enterica and underscore the public health risk posed by antimicrobial-resistant foodborne pathogens.