Isolation, Risk Factors, and Antimicrobial Resistance of Escherichia coli and Salmonella in Diarrheic Calves in Sebeta, Ethiopia.

Abstract

Calf diarrhea is a major constraint to dairy production in Ethiopia, resulting in substantial economic losses and potentially complicated by antimicrobial-resistant bacterial pathogens. This study aimed to determine the isolation of Escherichia coli and Salmonella in diarrheic calves, identify associated risk factors, and assess antimicrobial susceptibility patterns. A cross-sectional study was conducted in calves less than 2 months of age in and around Sebeta Town. The study area and districts were selected purposively, dairy farms were selected by simple random sampling, and diarrheic calves were selected purposively. A total of 129 fecal samples were collected and examined using standard bacteriological techniques and Biolog identification. Antimicrobial susceptibility testing was performed using the disk diffusion method. E. coli and Salmonella were isolated from 65 (50.3%; 95% CI: 41.6-59.1) and 8 (6.2%; 95% CI: 1.98-10.4) of the 129 samples, respectively. In multivariable logistic regression, sex, age, colostrum feeding, bedding, and housing were significantly associated with increased odds of E. coli isolation. For Salmonella sex, age, and bedding were significantly associated with increased odds of isolation. Most E. coli isolates were susceptible to sulphamethoxazole-trimethoprim (93.85%), polymyxin B (78.46%), gentamicin (76.92%), and ampicillin (73.85%), whereas tetracycline showed the highest resistance (58.46%). Among the 20 E. coli isolates exhibiting resistance to two or more antimicrobial agents, three of twenty (15.0%) fulfilled the predefined multidrug resistance criterion. All Salmonella isolates were susceptible to sulphamethoxazole-trimethoprim and polymyxin B, while 87.5% were susceptible to tetracycline and ampicillin. These findings demonstrate the isolation of E. coli and Salmonella among diarrheic calves and highlight important calf-management factors associated with bacterial isolation, as well as tetracycline resistance among E. coli. Improved calf management, appropriate colostrum feeding, adequate bedding, and prudent antimicrobial use are recommended. Further molecular characterization is warranted to determine the specific diarrheagenic E. coli pathotypes and clarify their contribution to calf diarrhea.