CTX-M-123, a novel hybrid of the CTX-M-1 and CTX-M-9 Group β-lactamases recovered from Escherichia coli isolates in China.

The chimeric bla(CTX-M-123) gene was identified in two ceftazidime-resistant Escherichia coli isolates from animals in different Chinese provinces. Like other CTX-M-1/9 group hybrids (CTX-M-64 and CTX-M-132), the ends (amino acids 1 to 135 and 234 to 291) of CTX-M-123 match CTX-M-15 while the central part (122 to 241) matches CTX-M-14. bla(CTX-M-123) is carried on related, but not identical, ~90-kb IncI1 plasmids in the two isolates, and one isolate simultaneously carries the group 1 blaCTX-M-55 gene on an additional IncI2 plasmid.