Korean J Clin Microbiol.  2011 Mar;14(1):24-29. 10.5145/KJCM.2011.14.1.24.

Comparison of Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing Breakpoints for β-Lactams in Enterobacteriaceae Producing Extended-Spectrum β-Lactamases and/or Plasmid-Mediated AmpC β-Lactamases

• Song W
• Park MJ
• Kim HS
• Kim JS
• Kim HS
• Lee KM

• KMID: 1449495
• DOI: http://doi.org/10.5145/KJCM.2011.14.1.24

Abstract

BACKGROUND
In 2010, the Clinical and Laboratory Standards Institute (CLSI) revised breakpoints for cephalosporins and carbapenems and indicated that extended-spectrum beta-lactamase (ESBL) testing is no longer necessary for Enterobacteriaceae. We compared the results of the CLSI 2010 and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) MIC breakpoints for Enterobacteriaceae producing ESBL and/or plasmid-mediated AmpC beta-lactamase (PABL).
METHODS
A total of 94 well-characterized clinical isolates of Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Salmonella spp., Shigella spp., Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, and Serratia marcescens were analyzed. Of them, 57 were ESBL producers, 24 were PABL producers, and 13 were ESBL plus PABL co-producers. Broth microdilution MIC tests were performed for cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem.
RESULTS
Among the 94 isolates containing ESBL and/or PABL, the number of isolates that were susceptible to cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem according to the CLSI 2010 vs. the EUCAST breakpoints were 4 (4.3%) vs. 4 (4.3%); 26 (27.7%) vs. 8 (8.5%); 37 (39.4%) vs. 14 (14.9%); 71 (75.5%) vs. 31 (33.0%); and 76 (80.9%) vs. 90 (95.7%), respectively. Of the 18 isolates that were not susceptible to imipenem according to the CLSI 2010 breakpoints, 13 isolates (72.2%) were P. mirabilis.
CONCLUSION
The CLSI 2010 MIC breakpoints without tests to detect ESBL and/or PABL for Enterobacteriaceae could be unreliable. Thus, special tests for ESBLs and AmpC beta-lactamases are required to detect the resistance mechanisms involved.

Keyword

CLSI; EUCAST; Enterobacteriaceae; Breakpoint

MeSH Terms

Aztreonam
Bacterial Proteins
beta-Lactamases
beta-Lactams
Carbapenems
Cefotaxime
Ceftazidime
Cephalosporins
Citrobacter freundii
Enterobacter aerogenes
Enterobacter cloacae
Enterobacteriaceae
Escherichia coli
Imipenem
Klebsiella oxytoca
Klebsiella pneumoniae
Proteus mirabilis
Salmonella
Serratia marcescens
Shigella
Aztreonam
Bacterial Proteins
Carbapenems
Cefotaxime
Ceftazidime
Cephalosporins
Imipenem
beta-Lactamases
beta-Lactams

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