Prevalence of Multidrug Resistant Phenotype in Escherichia coli Isolated from Swine Reared for Human Consumption in Abakaliki, South Eastern Nigeria

Abstract

Background: Escherichia coli is a commensal bacterium of the gastrointestinal tract of swine, but it can serve as a reservoir for antimicrobial resistance genes that pose significant public health risks through the food chain. This study assessed the prevalence, antimicrobial resistance profiles and multidrug resistance phenotypes of E. coli isolated from the nasal cavities of pigs reared for human consumption in Abakaliki, Nigeria. Methods: A total of 200 nasal swab samples were collected from two intensive pig farms (OLUPA Pig Farm and ADCT Pig Farm) in Abakaliki, representing piglets, young/immature pigs and hogs/older pigs. Standard microbiological methods were used for isolation and identification. Antibiotic susceptibility testing was performed using the Kirby-Bauer disc diffusion method, and the multiple antibiotic resistance index (MARI) was calculated. Results: E. coli was isolated from 36 (18.0%) of the 200 samples, with isolation rates of 16 (8.0%) at OLUPA Pig Farm and 20 (10.0%) at ADCT Pig Farm, and there was no significant difference between farms (p = 0.414). Grower/finisher pigs had the highest isolation rate (52.8%), which was statistically significant compared with other age groups (p = 0.035). All isolates exhibited 100% resistance to colistin, cefoxitin, imipenem, ceftazidime, aztreonam, and cefotaxime. Tetracycline resistance showed significant farm-level variation (p < 0.001): it was observed in all isolates at OLUPA Farm (100%) but in only 50% of isolates at ADCT Farm. High susceptibility (100%) was observed for ciprofloxacin, gentamicin, and ofloxacin. MARI values ranged from 0.3 to 0.6, with an overall mean of approximately 0.45 and no significant difference between farms (p = 0.188). However, within OLUPA Farm, adult/breeding pigs exhibited significantly higher MAR indices than piglets (p = 0.020). Conclusion: The nasal cavities of pigs harboured multidrug-resistant E. coli showing resistance to critically important antibiotics, including colistin and carbapenems. However, colistin resistance was assessed using disc diffusion, which is not the recommended method; confirmation by broth microdilution is required. These findings support the need for improved antimicrobial stewardship, routine surveillance and strict regulations on antibiotic use in pig production to reduce the public health risk posed by antibiotic-resistant E. coli from swine operations.