Clinical implementation of 2010 reference standards of the U.S.Chinical and Laboratory Standards Institute in antimicrobial susceptibility for Enterobacteriaceae

Abstract

Objective To compare the performance of 2009 and 2010 reference standards of the United States Clinical and Laboratory Standards Institute(CLSI)in antimicrobial susceptibility for Enterobacteriaceae.Methods The breakpoints of susceptibility for ceftriaxone,ceftazidime and aztreonam in CLSI M100-S19(2009)were used to analyze results of antimicrobial susceptibility of Escherichia coli (308 isolates)and Klebsiella pneumoniae(194 isolates),as well as those revised in M100-S20(2010).Results With both the breakpoints in CLSI M100-S19(2009)and CLSI M100-S20(2010),proportions of antimicmbial resistance of ceftriaxone,ceftazidime and aztreonam for isolates of extended-spectrum β-lactamases(ESBLs)-producing E. coli were 84.2 percent vs.98.0 percent and 84.9 percent vs.98.0percent,respectively:those for isolates of ESBLs negative E. coli were 4.2 percent vs.7.7 percent and 5.6percent vs.8.4 percent,respectively;those for isolates of ESBLs positive Klebsiella spp.were 67.2 percent vs.90.2 percent and 67.2 percent vs.90.2 percent,respectively:and those for isolates of ESBLs negative Klebsiella spp.were 9.8 percent vs.10.6 percent and 10.6 percent vs.10.6 percent,respectively.Conclusions Proportions of antimicrobial resistance for ceftriaxone,ceftazidime and aztreonam with the rcference breakpeints of CLSI M100-S20(2010)increase to various extent,8.8 compared to those with the old ones in 2009.Compared with ESBLs negative isolates,ESBLs positive isolates are affected much more by the breakpeints of CLSI M100-S20(2010).Proportion of affected Klebsiella spp.by the revised breakpoints of CLSI M100-S20(2010)for ceftazidime and aztreonam is higher than that of E. coli with ESBLs positive. Key words: Enterobacteriaceae; Microbial sensitivity tests; Reference standard