Emergence and co-existence of ESBL-producing and mcr-1-mediated colistin-resistant Escherichia coli isolated from camel milk.

The emergence of extended-spectrum β-lactamase (ESBL) and mcr-1 genes in Escherichia coli (E. coli) in camel milk severely limits therapeutic options for treating multidrug-resistant bacterial infections. The present study focused on the prevalence, co-occurrence pattern, and antibiogram characteristics of ESBL and colistin-resistant E. coli isolated from milk samples of camels. Overall, 384 camel milk samples were collected aseptically and cultured for the isolation and confirmation of E. coli using standard microbiological procedures, followed by molecular confirmation. Phenotypic ESBL was assessed employing the combined disk diffusion method, while colistin resistance was determined through broth microdilution. Molecular detection of blaCTX-M, blaTEM, and mcr-1 genes was performed by PCR, followed by co-existence pattern and antibiogram analysis of ESBL and colistin-resistant E. coli isolates. Overall, E. coli was confirmed in 20.57% of milk samples. Among these isolates, 58.23% were phenotypically positive for ESBL, while 49.37% showed phenotypic resistance to colistin. The blaCTX-M, blaTEM, and mcr-1 genes were identified in 41.77%, 31.65%, and 26.58% of E. coli isolates, respectively. Co-occurrence of antimicrobial resistance genes revealed that blaTEM + blaCTX-M was detected in 12.66%, while blaTEM + mcr-1 genes were detected in 5.06% of isolates, and mcr-1 was detected alone in only 5.06% of isolates. Antibiogram analysis showed high resistance to amoxicillin, cefepime, and oxytetracycline. The findings of the current study highlight the importance of routine antimicrobial resistance surveillance and prudent antimicrobial use in camel production systems.