Antibiotic susceptibility of haemolytic E. coli strains isolated from diarrhoeic faeces of buffalo calves

We investigated the antibiotic resistance of a collection of 94 strains (55.6%) of haemolytic Escherichia coli (E. coli) isolated in 169 diarrhoeic faecal samples from buffalo (Bubalus Bubalis) calves. Bacterial colonies on McConkey and EHLY agar that showed the morphology of E. coli were biochemically tested and then, furtherly classified as haemolytic, using PCR-based assays for enterohemorrhagic E. coli hly (hlyEHEC) virulence gene. When the pathogenic isolates were tested for their susceptibility to 13 different antibiotics, each tested isolate was found to be highly resistant to more than three antibiotics. In fact, absolute resistance (100% of resistance) to penicillin G, lincomycin, neomycin, was detected. Amoxicillin/clavulonic acid and ampicillin were found to be moderately effective against the majority of isolates (46.8% of resistance). Thirty-two (34%) of the haemolytic E. coli strains were phenotypically resistant to tetracycline. None of the isolated strains of E. coli was resistant to colistin sulfate. We conclude that the high prevalence of antimicrobial resistance detected in our study is a source of concern, and cautious use of antibiotics in food producing animals is highly recommended.