Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology

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pISSN 2288-0585 eISSN 2288-6850

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

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 2011 March, Volume 14, Issue 1, pages 24-29.

https://doi.org/10.5145/ACM.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

Wonkeun Song, Min-Jeong Park, Han-Sung Kim, Jae-Seok Kim, Hyun Soo Kim, Kyu Man Lee

Department of Laboratory Medicine, Hallym University College of Medicine, Seoul, Korea

Abstract

Background: In 2010, the Clinical and Laboratory Standards Institute (CLSI) revised breakpoints for cephalosporins and carbapenems and indicated that extended-spectrum β-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 β-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 β-lactamases are required to detect the resistance mechanisms involved. (Korean J Clin Microbiol 2011;14:24-29)

Keywords

 CLSI, EUCAST, Enterobacteriaceae, Breakpoint