CTX-M-190, a novel β-lactamase resistant to tazobactam and sulbactam identified in an Escherichia coli clinical isolate

ABSTRACT A novel β-lactamase, CTX-M-190, derived from CTX-M-55 by a single substitution of Ser for Thr at position 133 (Ser133Thr), was identified in a natural Escherichia coli clinical isolate. CTX-M-190 exhibited potent hydrolytic activity against cefotaxime, with a k cat / K m ratio of 14.5 μM −1 s −1 , and was highly resistant to inhibition by the β-lactamase inhibitors tazobactam and sulbactam, whose 50% inhibitory concentrations were 77- and 55-fold higher, respectively, for CTX-M-190 than for CTX-M-55. bla CTX-M-190 was located within the genetic platform IS Ecp1-bla CTX-M - orf477 , which was harbored by a 70-kb IncI1 plasmid.