Antimicrobial resistance to cefotaxime and ertapenem in Enterobacteriaceae: the effects of altering clinical breakpoints

Po-Yu Liu,Zong-Yen Wu,Ching-Lin Shyu,Chin-Fu Lin,Kwong-Chung Tung,Yi-Ching Huang,Jai-Wen Liu,Kun-Wei Chan,Chih-Chuan Kao,Zhi-Yuan Shi

doi:10.3855/jidc.3335

Abstract

The Clinical and Laboratory Standards Institute (CLSI) updated its antimicrobial susceptibility testing interpretation criteria for Enterobacteriaceae. This study assessed the effects of clinical breakpoint changes in the CLSI 2009 to 2012 guidelines on antibiotic susceptibility testing reports. In total, 2,076 non-duplicate clinical isolates of Enterobacteriaceae were analyzed. The disk diffusion method was used for susceptibility testing. The CLSI 2009-12 clinical breakpoints were applied to determine susceptibility of cefotaxime and ertapenem. Combined-disk testing was used for phenotypic confirmation of extended-spectrum beta-lactamase (ESBL) production. In total, Enterobacteriaceae resistance rates to cefotaxime increased from 13.1% using the CLSI 2009 guidelines to 23.6% with the CLSI 2010-12 guidelines, and the resistance rates to ertapenem were 0.4%, 1.0% and 0.8% with CLSI 2009, 2011 and 2012, respectively. Based on the 2010-12 CLSI criteria, all ESBL-producing Escherichia coli and Klebsiella pneumoniae were resistant to cefotaxime. Marked differences in susceptibility to ertapenem between the 2009 CLSI criteria and 2012-12 CLSI criteria were noted in ESBL-producing K. pneumoniae. Breakpoints changes in the updated CLSI guidelines resulted in higher resistance rates to cefotaxime and ertapenem. In addition, the effects were different in individual Enterobacteriaceae species. As a result, clinicians may opt to use alternative antimicrobial agents. Upon implementation of the newer CLSI guidelines, laboratories should be aware of the possible consequences and closely monitor the effects.

Highlights

The Clinical and Laboratory Standards Institute (CLSI) updated its antimicrobial susceptibility testing interpretation criteria for Enterobacteriaceae
E. coli and K. pneumoniae together accounted for 67.3% of all Enterobacteriaceae isolated
Resistance rates to cefotaxime increased from 13.1% (CLSI 2009) to 23.6% (CLSI 2010-12)

Summary

Introduction

The Clinical and Laboratory Standards Institute (CLSI) updated its antimicrobial susceptibility testing interpretation criteria for Enterobacteriaceae. Conclusions: Breakpoints changes in the updated CLSI guidelines resulted in higher resistance rates to cefotaxime and ertapenem. Antimicrobial susceptibility testing is one of the most important tasks in clinical microbiology laboratories It is a valuable guide for antibiotic therapy and an important epidemiological tool to monitor resistant organisms. The CLSI updated and included its recommendations into the CLSI 2010, 2011 and 2012 guidelines, which include major changes in the antibiotic susceptibility testing for Enterobacteriaceae. With the increase of cephalosporin breakpoints in the CLSI 2010-12 guidelines, it is no longer necessary to detect extended-spectrum beta–lactamase (ESBL) producers and to adjust all cephalosporin sensitivity results to resistance, as previously recommended by CLSI 2009 guideline

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