High prevalence of ESBL-producing E. coli phylogroup B2 clinical isolates in northeastern Thailand

Production of extended-spectrum β-lactamases (ESBLs) is a common resistance mechanism in Enterobacteriaceae, leading to serious hospital-acquired infections. This study aimed to assess phenotypic, phylogenetic, and antibiotic resistance patterns among ESBL-producing Escherichia coli isolates recovered from two rural tertiary hospitals in Thailand.

Among 467 Enterobacteriaceae isolates, E. coli was the most prevalent 356 (76.2%) followed by K. pneumoniae 88 (18.8%), K. aerogenes 8 (1.7%), K. variicola 3 (0.6%), K. quasipneumoniae 1 (0.2%%), K. oxytoca 1 (0.2%), and unidentified 9 (1.9%). Of the 202 cephalosporin-resistant E. coli isolates, 195 (96.5%) were ESBL-producing and 7 (3.5%) were non-ESBL-producing. Clermont typing revealed that phylogroup B2 was predominant (43.3%), followed by phylogroups F (11.3%), D (10.3%), C (9.7%), and A (8.7%). Among the beta-lactamase-encoding genes, bla_CTX-M (83.6%) and bla_TEM (81.0%) were widely found among the isolates, and bla_CTX-M-1 (60.7%) was the most common among the five bla_CTX-M subgroups detected. The predominant ESBL was bla_CTX-M-15 (58.3%). All isolates were resistant to cefotaxime (100%) and ampicillin (100%), followed by ciprofloxacin (91.3 %), ceftazidime (72.8 %), and tetracycline (64.1%).

Our findings show that phylogroup B2 was the most prevalent phylogroup among ESBL-producing E. coli isolates in northeastern Thailand. Notably, the isolates mostly carried the bla_CTX-M gene(s).