Multidrug-resistant ESBL-producing Escherichia coli coexisting with colistin-resistance genes in pig farms, Central Thailand

The presence of extended-spectrum beta-lactamase and colistin resistance E. coli in food-producing animals is a public health concern. This study was conducted using a rigorous methodology to survey the prevalence of ESBL-producing and colistin-resistant E. coli from pig farms in the central part of Thailand. A total of 519 samples were collected from fecal, feed, and waste in 53 farms located in central Thailand. All samples were inoculated onto selective agar, and species identification was performed using biochemical assays and MAlDI-TOF MS. Antimicrobial susceptibility was determined by broth microdilution, and ESBL production was confirmed by the combination disc diffusion method. Resistance genes were detected by PCR and confirmed by sequencing. Thirty-four isolates from fecal and waste samples were identified as ESBL-producing E. coli. All were considered multidrug-resistant, resisting to beta-lactams, aminoglycosides, quinolones, and colistin. The blaCTX-M Group 1 was detected in all isolates, with additional blaCTX-M Group 2 (74%) in some isolates. Furthermore, 94% of these ESBL-producing E.coli were found to coexist with mcr-1 and/or mcr-3. In conclusion, this surveillance study found that although the prevalence of ESBL-producing E. coli is low in pig farms, the co-occurrence of blaCTX-M and mcr- genes is high among positive isolates. Therefore, the results indicated a chance that ESBL and colistin resistance genes may exist together in one bacterial isolate, raising threats in treatment for bacterial infections. Further analysis is needed to indicate the location and transferability of these genes in order to understand how to prevent the dissemination of these resistance pathogens in the future.