Prevalence of ST1193 clone and IncI1/ST16 plasmid in E-coli isolates carrying bla_CTX-M-55 gene from urinary tract infections patients in China

To study molecular epidemiology of CTX-M-55-carrying Escherichia coli isolates from urinary tract infections (UTIs) in China. 111 bla_CTX-M-55-positive E.coli isolates from UTIs patients in China were studied. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were used to analyze the homologies among the strains. Conjugation experiments, S1nuclease PFGE and PCR analysis were performed to characterize plasmids harboring bla_CTX-M-55 and their genetic environment. 111 isolates were clustered into 86 individual pulsotypes and three clusters by PFGE. Fifty-five (49.5%) of the isolates belonged to 8 STs. Most of the ST1193 isolates belonged to one PFGE cluster. Transconjugants (n = 45) derived from randomly selected bla_CTX-M-55 donors (n = 58), were found to contain a single 90-kb conjugative plasmid, which mainly belonged to the IncI1 groups (34, 76%). Among the IncI1 plasmids, the bla_CTX-M-55/IncI1/ST16 predominated (23/34, 68%). The bla TEM-1 and aac (3′)-II genes were frequently detected on the IncI1 plasmids, and the insertion of ISEcp1 or IS26 was observed at the 48 bp or 45 bp upstream of the start codon of bla_CTX-M-55 gene. The dissemination of bla_CTX-M-55 gene among E. coli UTI isolates, appeared to be due to both the major clonal lineage of ST1193 and the horizontal transfer of epidemic plasmid IncI1/ST16.