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Song, Park, Kim, Kim, Kim, and Lee: Comparison of Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing Breakpoints for β-Lactams in Enterobacteriaceae Producing Extended-Spectrumβ-Lactamases and/or Plasmid-Mediated AmpCβ-Lactamases
Original Article

Korean J Clin Microbiol 2011;14(1):24-29.

Published online: 21 March 2011

DOI: https://doi.org/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-Spectrumβ-Lactamases and/or Plasmid-Mediated AmpCβ-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

Correspondence: Wonkeun Song, Department of Laboratory Medicine, Kangnam Sacred Heart Hospital, 948-1 Daelim 1-dong, Youngdeungpo-gu, Seoul 150-950, Korea. (Tel) 82-2-829-5259, (Fax) 82-2-847-2403, (E-mail) swonkeun@hallym.or.kr

Received 4 May 2010       Revised 28 June 2010       Accepted 20 July 2010

Copyright © 2011 Korean Journal of Clinical Microbiology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: CLSI, EUCAST, Enterobacteriaceae, Breakpoint

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Table 1.
MIC interpretive standards of CLSI and EUCAST in Enterobacteriaceae
Antimicrobial agent MIC interpretive standard (μg/mL): susceptible/intermediate/resistant
CLSI EUCAST 2010
2009 2010
Cefazolin ≤8/16/≥32 ≤1/2/≥4 −
Cefotaxime ≤8/16∼32/≥64 ≤1/2/≥4 ≤1/2/≥4
Ceftriaxone ≤8/16∼32/≥64 ≤1/2/≥4 ≤1/2/≥4
Ceftizoxime ≤8/16∼32/≥64 ≤1/2/≥4 −
Ceftazidime ≤8/16/≥32 ≤4/8/≥16 ≤2/4∼8/≥16
Aztreonam ≤8/16/≥32 ≤4/8/≥16 ≤1/2∼8/≥16
Cefepime ≤8/16/≥32 ≤8/16/≥32 ≤1/2∼8/≥16
Doripenem − ≤1/2/≥4 ≤1/2/≥4
Ertapenem ≤2/4/≥8 ≤0.25/0.5/≥1 ≤0.5/1/≥2
Imipenem ≤4/8/≥16 ≤1/2/≥4 ≤2/4∼8/≥16
Meropenem ≤4/8/≥16 ≤1/2/≥4 ≤2/4∼8/≥16
Table 2.
Results of antimicrobial susceptibility testing by the CLSI 2010 and the EUCAST interpretation criteria for isolates containing ESBL and/or plasmid-mediated AmpC β-lactamase
Organism β-Lactamase (No. of isolates) Reference No. of isolates susceptible (resistant) by CLSI/EUCAST
CTX CAZ ATM FEP IPM
E. coli SHV-12 (2) 7 0/0 (2/2) 0/0 (2/2) 0/0 (2/2) 2/1 (0/0) 2/2 (0/0)
  TEM-8 (1) K. Lee 1/1 (0/0) 0/0 (1/1) 1/0 (0/0) 1/1 (0/0) 1/1 (0/0)
  CTX-M-3 (2) 7 0/0 (2/2) 1/0 (0/0) 0/0 (1/1) 0/0 (2/2) 2/2 (0/0)
  CTX-M-14 (4) 7 0/0 (4/4) 4/1 (0/0) 1/0 (0/0) 1/0 (0/3) 4/4 (0/0)
  CTX-M-15 (1) 7 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0)
  DHA-1 (2) 7 0/0 (2/2) 0/0 (2/2) 1/0 (1/1) 2/2 (0/0) 2/2 (0/0)
  CMY-1 (3) 7 0/0 (3/3) 1/0 (2/2) 1/0 (2/2) 3/1 (0/0) 3/3 (0/0)
  CMY-2 (2) 7 0/0 (2/2) 0/0 (2/2) 0/0 (1/1) 2/2 (0/0) 2/2 (0/0)
  SHV-12 plus DHA-1 (1) 8 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0) 1/1 (0/0)
  CTX-M-14 plus DHA-1 (2) 8 0/0 (2/2) 2/0 (0/0) 2/0 (0/0) 2/0 (0/0) 2/2 (0/0)
  CTX-M-14 plus CMY-2 (1) 8 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0)
  CTX-M-15 plus DHA-1 (2) 8 0/0 (2/2) 0/0 (1/1) 0/0 (2/2) 0/0 (1/2) 1/2 (0/0)
  CTX-M-15 plus CMY-10 (1) 8 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0)
  Subtotal (24)   1/1 (23/23) 8/1 (14/14) 6/0 (13/13) 14/8 (6/10) 23/24 (0/0)
K. oxytoca DHA-1 (3) 9 1/1 (1/1) 0/0 (1/1) 2/2 (0/0) 3/3 (0/0) 3/3 (0/0)
  SHV-12 plus DHA-1 (1) 9 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/0)
  Subtotal (4)   1/1 (2/2) 0/0 (2/2) 2/2 (1/1) 3/3 (1/1) 3/3 (1/0)
K. pneumoniae SHV-2 (1) K. Lee 0/0 (1/1) 0/0 (1/1) 0/0 (0/0) 1/0 (0/0) 1/1 (0/0)
  SHV-2a (2) 9 0/0 (2/2) 0/0 (2/2) 0/0 (1/1) 2/0 (0/0) 2/2 (0/0)
  SHV-5 (1) 9 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0) 1/1 (0/0)
  SHV-12 (2) 9 0/0 (2/2) 1/0 (1/1) 0/0 (1/1) 1/0 (0/1) 2/2 (0/0)
  TEM-52 (1) 9 0/0 (1/1) 0/0 (1/1) 1/0 (0/0) 1/0 (0/0) 1/1 (0/0)
  CTX-M-9 (1) 9 0/0 (1/1) 1/0 (0/0) 1/0 (0/0) 1/0 (0/0) 1/1 (0/0)
  CTX-M-14 (3) 9 0/0 (3/3) 3/0 (0/0) 1/0 (0/0) 3/0 (0/0) 3/3 (0/0)
  GES-5 (2) 9 0/0 (2/2) 0/0 (2/2) 0/0 (2/2) 0/0 (1/2) 1/2 (0/0)
  DHA-1 (4) 9 1/1 (3/3) 0/0 (4/4) 2/0 (2/2) 4/4 (0/0) 4/4 (0/0)
  CMY-1 (3) 9 0/0 (3/3) 1/0 (2/2) 3/0 (0/0) 3/2 (0/0) 3/3 (0/0)
  SHV-12 plus DHA-1 (4) 9 0/0 (4/4) 0/0 (4/4) 0/0 (4/4) 3/2 (0/1) 4/4 (0/0)
  Subtotal (24)   1/1 (23/23) 6/0 (18/18) 8/0 (11/11) 20/9 (1/4) 23/24 (0/0)
P. mirabilis TEM-52 (2) K. Lee 0/0 (2/2) 1/0 (1/1) 2/1 (0/0) 2/1 (0/0) 0/2 (0/0)
  CTX-M-12 (3) This study 0/0 (3/3) 1/1 (2/2) 2/1 (0/0) 2/0 (1/1) 1/3 (0/0)
  CTX-M-14 (2) K. Lee 0/0 (2/2) 2/2 (0/0) 2/2 (0/0) 2/0 (0/0) 1/2 (0/0)
  CTX-M-15 (3) This study 0/0 (3/3) 3/1 (0/0) 3/1 (0/0) 1/0 (1/2) 1/3 (0/0)
  DHA-1 (2) This study 1/1 (1/1) 1/1 (1/1) 2/2 (0/0) 2/2 (0/0) 0/0 (2/0)
  CMY-2 (4) This study 0/0 (4/4) 0/0 (2/2) 4/4 (0/0) 4/4 (0/0) 0/4 (0/0)
  SHV-12 plus CTX-M-14 This study 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (0/1) 1/1 (0/0)
  plus DHA-1 (1)            
  Subtotal (17)   1/1 (16/16) 8/5 (7/7) 15/11 (1/1) 13/7 (2/4) 4/15 (2/0)
Salmonella CTX-M-15 (1) 10 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0)
  CMY-2 (1) 9 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/0 (0/0) 1/1 (0/0)
  Subtotal (2)   0/0 (2/2) 0/0 (2/2) 0/0 (2/2) 1/0 (1/1) 2/2 (0/0)
Shigella CTX-M-14 (3) 11 0/0 (3/3) 3/1 (0/0) 3/0 (0/0) 3/0 (0/0) 3/3 (0/0)
C. freundii SHV-12 (3) 12 0/0 (3/3) 0/0 (3/3) 0/0 (3/3) 3/2 (0/0) 3/3 (0/0)
  TEM-52 (1) 12 0/0 (1/1) 0/0 (1/1) 1/0 (0/0) 1/0 (0/0) 1/1 (0/0)
  Subtotal (4)   0/0 (4/4) 0/0 (4/4) 1/0 (3/3) 4/2 (0/0) 4/4 (0/0)
E. aerogenes SHV-12 (1) 12 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/0 (0/0) 1/1 (0/0)
  TEM-52 (2) 12 0/0 (2/2) 0/0 (2/2) 0/0 (1/1) 2/0 (0/0) 1/2 (0/0)
  CTX-M-14 (1) 12 0/0 (1/1) 1/1 (0/0) 1/1 (0/0) 0/0 (0/1) 0/0 (1/0)
  Subtotal (4)   0/0 (4/4) 1/1 (3/3) 1/1 (2/2) 3/0 (0/1) 2/3 (1/0)
E. cloacae SHV-12 (3) 12 0/0 (3/3) 0/0 (3/3) 0/0 (3/3) 3/0 (0/0) 3/3 (0/0)
  CTX-M-3 (1) 12 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0)
  CTX-M-9 (1) 12 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/1 (0/0) 1/1 (0/0)
  SHV-12 plus CTX-M-9 (3) 12 0/0 (3/3) 0/0 (3/3) 0/0 (3/3) 2/0 (1/1) 3/3 (0/0)
  Subtotal (8)   0/0 (8/8) 0/0 (8/8) 0/0 (8/8) 6/1 (2/2) 8/8 (0/0)
S. marcescens SHV-12 (1) 12 0/0 (1/1) 0/0 (1/1) 0/0 (1/1) 1/0 (0/0) 1/1 (0/0)
  TEM-52 (3) 12 0/0 (3/3) 0/0 (3/3) 1/0 (0/0) 3/1 (0/0) 3/3 (0/0)
  Subtotal (4)   0/0 (4/4) 0/0 (4/4) 1/0 (1/1) 4/1 (0/0) 4/4 (0/0)
  Total (94)   4/4 (89/89) 26/8 (62/62) 37/14 (42/42) 71/31 (13/23) 76/90 (4/0)

Abbreviations: CTX, cefotaxime; CAZ, ceftazidime; ATM, aztreonam; FEP, cefepime; IPM, imipenem.

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