title: Antimicrobial resistance to cefotaxime and ertapenem in Enterobacteriaceae: the effects of altering clinical breakpoints.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Taichung Veterans General Hospital, Taichung, Taiwan. idfellow@gmail.com.
authors.forename: Po-Yu
authors.initials: PY
authors.lastname: Liu
authors.forename: Zhi-Yuan
authors.initials: ZY
authors.lastname: Shi
authors.forename: Kwong-Chung
authors.initials: KC
authors.lastname: Tung
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Shyu
authors.forename: Kun-Wei
authors.initials: KW
authors.lastname: Chan
authors.forename: Jai-Wen
authors.initials: JW
authors.lastname: Liu
authors.forename: Zong-Yen
authors.initials: ZY
authors.lastname: Wu
authors.forename: Chih-Chuan
authors.initials: CC
authors.lastname: Kao
authors.forename: Yi-Ching
authors.initials: YC
authors.lastname: Huang
authors.forename: Chin-Fu
authors.initials: CF
authors.lastname: Lin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002439:Cefotaxime / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000201:enzymology*; D004756:Enterobacteriaceae Infections / Q000382:microbiology; D000077727:Ertapenem; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000592:standards; D018440:beta-Lactam Resistance; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D000077727:Ertapenem; D002439:Cefotaxime