High rates of susceptibility to ceftazidime among globally prevalent CTX-M-producing Escherichia coli: potential clinical implications of the revised CLSI interpretive criteria
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Abstract
The CTX-M family of extended-spectrum β-lactamases (ESBLs) is a significant global public health threat. The prevalence of specific bla CTX-M genes varies geographically, but bla CTX-M-15 and bla CTX-M-14 dominate in most countries. We applied the latest Clinical Laboratory Standards Institute (CLSI) interpretive criteria (M100-S20) to a diverse collection of ESBL-producing Escherichia coli strains obtained from clinical specimens in our laboratory. Whereas under previous CLSI recommendations all isolates in this strain collection would have been reported as ceftazidime-resistant, under the new recommendations, approximately 11% of CTX-M-15-producing E. coli and 93% of CTX-M-14-producing E. coli respectively tested as ceftazidime-susceptible. We also found that, whilst many CTX-M-14-producers had minimum inhibitory concentrations (MICs) less than the breakpoint of 4 mg/L, the MIC distribution for these strains was higher than that of wild-type E. coli, with one CTX-M-14-producing isolate having an MIC of >64 mg/L. Although the new CLSI recommendations imply that ceftazidime can be safely used to treat serious infections due to CTX-M-producing E. coli, clinical outcome data are lacking. Consequently, the widespread use of ceftazidime in this setting could have profound clinical implications.
Keywords
Minimum Inhibitory Concentration Ceftriaxone Ceftazidime Boronic Acid ESBL ProductionNotes
Conflict of interest
All authors report no conflict of interests.
Funding
No specific funding was required for this study.
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