Genotypic and phenotypic evidence of extended-spectrum β-lactamase and carbapenemase-producing shigatoxigenic and intimin-producing Escherichia coli in diarrheic calves in Bangladesh: A hidden zoonotic and public health risk.

Shiga toxin-producing Escherichia coli (STEC) is a pathotype of E. coli associated with a wide variety of diarrhoea in neonatal calves, causing a global economic loss in the dairy industry with significant zoonotic risks via STEC and intimin-producing STEC, resulting in enteric and systemic illness, including diarrhoea, haemorrhagic colitis (HC), and haemolytic uremic syndrome (HUS) in humans. The presence of multidrug-resistant (MDR) STEC in neonatal diarrhoeic calves represents a significant public health concern and limits available therapeutic options. This study investigated the presence of extended-spectrum β-lactamase (ESBL) and carbapenemase-producing STEC isolates and their genotypic combinations of virulence and resistance genes in diarrhoeal calves. A total of 75 rectal swabs from diarrhoeic calves aged ≤ 12 weeks were sampled from three districts of Bangladesh, screened using selective culture and polymerase chain reaction (PCR), followed by phenotypic antimicrobial susceptibility profiling and phenotypic and genotypic screening for ESBL- and carbapenemase-production. The E. coli isolation rate among diarrhoeic calves was 80% (60/75; 95% CI: 69.17-88.35). PCR screening revealed the presence of stx1, stx2, and eae virulence genes, and the prevalence of E. coli isolates harbouring these virulence genes was 13.33% (10/75; 95% CI: 6.5-23.1). The ten virulent isolates included five stx-positive, four stx/eae-positive and one eae-positive E. coli. All the virulent isolates (100%) were resistant to ciprofloxacin and meropenem; however, eight (80%) of the tested isolates were susceptible to gentamycin, and 60% were susceptible to amoxicillin-clavulanate. All virulent E. coli isolates were MDR. We observed that 5 (50%) of the virulent E. coli isolates were ESBL producers, and 7 (70%) were carbapenemase producers. The results for phenotypes and genotypes of ESBL- and carbapenemase-producing strains were not concordant. At least one ESBL gene was present in nine of the ten virulent isolates examined, including four ESBL phenotype-negative isolates. Carbapenemase-producing genotypes were significantly more common in isolates with multiple virulence genes than in those with a single virulence gene (p = 0.001). To the best of our knowledge, this is the first report on ESBL- and carbapenemase-producing MDR STEC in diarrhoeic calves in Bangladesh.