Occurrence of Escherichia coli carrying Shiga toxin-producing genes in buffaloes on smallholdings in Bangladesh

Background and Aim: Shiga toxin-producing Escherichia coli (STEC) has emerged as significant foodborne pathogens. Ruminants are the primary reservoir of the zoonotic STEC. In Bangladesh, previous studies reported the presence of STEC in cattle, goat, and sheep; however, there is little information about STEC carriage by buffaloes. This study aimed to determine the occurrence of STEC in healthy (absence of clinical signs and symptoms) buffaloes on smallholdings in Bangladesh and to assess the antimicrobial resistance pattern of identified STEC isolates. Materials and Methods: A total of 100 rectal swab samples were obtained from randomly selected buffaloes on 40 smallholdings in Chittagong Division, Bangladesh. Samples were subjected to bacteriological screening to identify E. coli. All E. coli isolates were examined for the presence of the Shiga toxin-producing genes - Shiga toxin 1 (stx1) and Shiga toxin 2 (stx2) using polymerase chain reaction. The antimicrobial susceptibility of identified STEC isolates was tested using the disk diffusion method. Results: Results show that 71 fecal samples were positive for E. coli in bacteriological screening. The proportion of buffaloes harboring STEC isolates was 11% (11/100) (95% confidence interval [CI] 6.1-18.8], of which 7% (7/100) (95% CI 3.2- 13.9) and 4% (4/100) (95% CI 1.2-10.2) carried stx1 and stx2 genes, respectively. Antibiogram revealed that 91% (10/11), 73% (8/11), 55% (6/11), and 55% (6/11) STEC isolates were resistant to tetracycline, sulfamethoxazole-trimethoprim, erythromycin, and ampicillin, respectively. In contrast, 91% (10/11) STEC isolates were sensitive to ciprofloxacin, chloramphenicol, and gentamicin, whereas 73% (8/11) isolates were sensitive to ceftriaxone. Conclusion: This study highlights, for the first time, a significant proportion of fecal samples from healthy buffaloes on smallholdings in Bangladesh harboring antimicrobial-resistant STEC. Transmission of antimicrobial-resistant STEC from buffaloes to humans could pose an added risk to public health in rural Bangladesh