CTX-M-190, a Novel β-Lactamase Resistant to Tazobactam and Sulbactam, Identified in an Escherichia coli Clinical Isolate

Abstract

A novel ␤-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 M Ϫ1 s Ϫ1 , and was highly resistant to inhibition by the ␤-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 was located within the genetic platform ISEcp1-bla CTX-M -orf477, which was harbored by a 70-kb IncI1 plasmid.T he high prevalence of CTX-M extended-spectrum ␤-lactamase (ESBL) genes in Enterobacteriaceae, particularly in Escherichia coli and Klebsiella pneumoniae, has been documented worldwide (1, 2). Since CTX-M-producing Enterobacteriaceae often confer resistance to many other antimicrobial agents, they constitute one of the most worrying problems in modern medical practice (2, 3). On the basis of the available evidence, ␤-lactam/␤-lactamase inhibitors (BLBLIs), such as piperacillin-tazobactam, remain active in vitro against a high proportion of CTX-M-producing Enterobacteriaceae and may provide a reasonable carbapenem-sparing option for ESBL producers (4). A recent surveillance program conducted across China, which included 196 ESBLproducing E. coli and 124 ESBL-producing K. pneumoniae strains, found bla CTX-M occurrence in 99.5% of E. coli strains and 91.1% of K. pneumoniae strains and indicated resistance rates of 2.6% and 4.8% to piperacillin-tazobactam in these two kinds of ESBL producers (5). BLBLI resistance in CTX-M-producing Enterobacteriaceae is frequently associated with the coexistence of OXA-1 ␤-lactamases (6), whereas no natural CTX-M variants have been reported to confer resistance to BLBLIs. Isolation of a clinical E. coli strain resistant to piperacillin-tazobactam.A clinical strain of E. coli HS37 was isolated from a urine specimen of a 56-year-old female outpatient with urinary tract infection in July 2015 at a university hospital in Shanghai, China. The Clinical and Laboratory Standards Institute (CLSI)-recommended double-disk synergy test confirmed the production of an ESBL by this isolate (7), while it displayed resistance to both piperacillin-tazobactam and ampicillin-sulbactam. The presence of a CTX-M-like ␤-lactamase in E. coli strain HS37 was confirmed by CTX-M-1 group-specific PCR and sequencing as previously described (8). The new CTX-M-1 group ␤-lactamase was derived from CTX-M-55 by a single substitution of Ser for Thr at position 133 (Ser133Thr) and was designated CTX-M-190 (Table 1).

Genetic and Functional Characterization of bla CTX-M-199 , a Novel Tazobactam and Sulbactam Resistance-Encoding Gene Located in a Conjugative mcr-1 -Bearing IncI2 Plasmid

“…These data suggest that the S 130 T mutation did not affect the binding of clavulanate and avibactam to CTX-M-64, which is very consistent with their resistance phenotypes. It should be noted that the IC 50 s determined for different enzymes were significantly different from that of CTX-M-190, which is probably due to the use of nontagged protein and nitrocefin as the substrate in this study (11). Ser 130 is one of the essential residues residing in the active site and involved in substrate catalysis in all class A ␤-lactamases.…”

Past and Present Perspectives on β-Lactamases

“…SHV ESBL variants are still identified, but few new TEM-related enzymes are now seen. Only recently have tazobactam-resistant CTX-M ␤-lactamases been identified, unusual enzymes that are still inhibited by clavulanic acid (128,129). The family of GES enzymes was initially believed to represent another set of ESBLs, but some GES variants with single point mutations have acquired the ability to hydrolyze carbapenems (130,131).…”

Reconciling the potentially irreconcilable? Genotypic and phenotypic amoxicillin-clavulanate resistance in Escherichia coli

“…One had a novel bla CTX-M variant (CTX-M-15-like, Ser130Gly mutation). Previous work on mechanisms of beta-lactamase inhibition suggests mutations at Ambler position 28 130 likely lead to inhibitor resistance 7 and indeed a similar mutation (Ser130Thr CTX-M-190) resultedin sulbactam and tazobactam resistance 29. The other two had antibiograms consistent with ampC hyper-production (cefoxitin resistant, ceftazidime resistant, cefepime susceptible), but we were unable to identify complete promoter sequences matching our reference (CP009072.1) in the region upstream of ampC, suggesting either assembly issues or insertion of alternative elements upstream of ampC drove increased expression.…”