Cephalosporin MIC distribution of extended-spectrum-β-lactamase- and pAmpC-producing Escherichia coli and Klebsiella species

Peggy C. Kohner, Frans J L Robberts, Franklin R. Cockerill, Robin Patel

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

The acquisition of β-lactamases in members of the Enterobacteriaceae family poses a challenge to antimicrobial susceptibility testing in the clinical laboratory. We correlated the distribution of the MICs for Klebsiella spp. and Escherichia coli with the presence of extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase (pAmpC) genes. A total of 264 isolates were subjected to cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime, and aztreonam agar dilution MIC determination; ESBL screening and confirmatory testing by the methods of the Clinical and Laboratory Standards Institute (CLSI); and for isolates for which the MICs of extended-spectrum cephalosporins were ≥1 μg/ml or the MICs of cefpodoxime were >4 μg/ml, PCR amplification and sequencing of the ESBL and pAmpC genes. PCR was positive for 73/81 isolates (45 isolates with an ESBL gene alone, 24 isolates with a pAmpC gene alone, with 4 isolates with both genes). Compared to PCR, confirmatory testing by the CLSI method yielded a sensitivity and a specificity of 98.0 and 96.3%, respectively; there were six false-positive results and one false-negative result. No distinction in the MIC distribution was apparent between isolates with the ESBL gene and isolates with the pAmpC gene. A substantial percentage of the isolates with PCR-confirmed ESBL and/or pAmpC genes fell within the current CLSI susceptible category. For a ceftazidime, ceftriaxone, or cefotaxime MIC of ≥2 μg/ml, a dichotomy existed between isolates with and without ESBL and pAmpC genes in most cases. This suggests that the presence of the ESBL and the pAmpC enzymes may yield similar MICs of extended-spectrum cephalosporins, many of which fall within the current nonresistant categories. Lowering of the current CLSI breakpoints for cephalosporins appears to be warranted.

Original languageEnglish (US)
Pages (from-to)2419-2425
Number of pages7
JournalJournal of Clinical Microbiology
Volume47
Issue number8
DOIs
StatePublished - Aug 2009

Fingerprint

Klebsiella
Cephalosporins
Plasmids
Escherichia coli
Genes
Polymerase Chain Reaction
Ceftazidime
Cefotaxime
Ceftriaxone
cefpodoxime
Aztreonam
Cefazolin
Enterobacteriaceae
Agar
Sensitivity and Specificity

ASJC Scopus subject areas

  • Microbiology (medical)

Cite this

Cephalosporin MIC distribution of extended-spectrum-β-lactamase- and pAmpC-producing Escherichia coli and Klebsiella species. / Kohner, Peggy C.; Robberts, Frans J L; Cockerill, Franklin R.; Patel, Robin.

In: Journal of Clinical Microbiology, Vol. 47, No. 8, 08.2009, p. 2419-2425.

Research output: Contribution to journalArticle

@article{c488db549c7b4b85a8351d31a31d21f7,
title = "Cephalosporin MIC distribution of extended-spectrum-β-lactamase- and pAmpC-producing Escherichia coli and Klebsiella species",
abstract = "The acquisition of β-lactamases in members of the Enterobacteriaceae family poses a challenge to antimicrobial susceptibility testing in the clinical laboratory. We correlated the distribution of the MICs for Klebsiella spp. and Escherichia coli with the presence of extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase (pAmpC) genes. A total of 264 isolates were subjected to cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime, and aztreonam agar dilution MIC determination; ESBL screening and confirmatory testing by the methods of the Clinical and Laboratory Standards Institute (CLSI); and for isolates for which the MICs of extended-spectrum cephalosporins were ≥1 μg/ml or the MICs of cefpodoxime were >4 μg/ml, PCR amplification and sequencing of the ESBL and pAmpC genes. PCR was positive for 73/81 isolates (45 isolates with an ESBL gene alone, 24 isolates with a pAmpC gene alone, with 4 isolates with both genes). Compared to PCR, confirmatory testing by the CLSI method yielded a sensitivity and a specificity of 98.0 and 96.3{\%}, respectively; there were six false-positive results and one false-negative result. No distinction in the MIC distribution was apparent between isolates with the ESBL gene and isolates with the pAmpC gene. A substantial percentage of the isolates with PCR-confirmed ESBL and/or pAmpC genes fell within the current CLSI susceptible category. For a ceftazidime, ceftriaxone, or cefotaxime MIC of ≥2 μg/ml, a dichotomy existed between isolates with and without ESBL and pAmpC genes in most cases. This suggests that the presence of the ESBL and the pAmpC enzymes may yield similar MICs of extended-spectrum cephalosporins, many of which fall within the current nonresistant categories. Lowering of the current CLSI breakpoints for cephalosporins appears to be warranted.",
author = "Kohner, {Peggy C.} and Robberts, {Frans J L} and Cockerill, {Franklin R.} and Robin Patel",
year = "2009",
month = "8",
doi = "10.1128/JCM.00508-09",
language = "English (US)",
volume = "47",
pages = "2419--2425",
journal = "Journal of Clinical Microbiology",
issn = "0095-1137",
publisher = "American Society for Microbiology",
number = "8",

}

TY - JOUR

T1 - Cephalosporin MIC distribution of extended-spectrum-β-lactamase- and pAmpC-producing Escherichia coli and Klebsiella species

AU - Kohner, Peggy C.

AU - Robberts, Frans J L

AU - Cockerill, Franklin R.

AU - Patel, Robin

PY - 2009/8

Y1 - 2009/8

N2 - The acquisition of β-lactamases in members of the Enterobacteriaceae family poses a challenge to antimicrobial susceptibility testing in the clinical laboratory. We correlated the distribution of the MICs for Klebsiella spp. and Escherichia coli with the presence of extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase (pAmpC) genes. A total of 264 isolates were subjected to cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime, and aztreonam agar dilution MIC determination; ESBL screening and confirmatory testing by the methods of the Clinical and Laboratory Standards Institute (CLSI); and for isolates for which the MICs of extended-spectrum cephalosporins were ≥1 μg/ml or the MICs of cefpodoxime were >4 μg/ml, PCR amplification and sequencing of the ESBL and pAmpC genes. PCR was positive for 73/81 isolates (45 isolates with an ESBL gene alone, 24 isolates with a pAmpC gene alone, with 4 isolates with both genes). Compared to PCR, confirmatory testing by the CLSI method yielded a sensitivity and a specificity of 98.0 and 96.3%, respectively; there were six false-positive results and one false-negative result. No distinction in the MIC distribution was apparent between isolates with the ESBL gene and isolates with the pAmpC gene. A substantial percentage of the isolates with PCR-confirmed ESBL and/or pAmpC genes fell within the current CLSI susceptible category. For a ceftazidime, ceftriaxone, or cefotaxime MIC of ≥2 μg/ml, a dichotomy existed between isolates with and without ESBL and pAmpC genes in most cases. This suggests that the presence of the ESBL and the pAmpC enzymes may yield similar MICs of extended-spectrum cephalosporins, many of which fall within the current nonresistant categories. Lowering of the current CLSI breakpoints for cephalosporins appears to be warranted.

AB - The acquisition of β-lactamases in members of the Enterobacteriaceae family poses a challenge to antimicrobial susceptibility testing in the clinical laboratory. We correlated the distribution of the MICs for Klebsiella spp. and Escherichia coli with the presence of extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase (pAmpC) genes. A total of 264 isolates were subjected to cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime, and aztreonam agar dilution MIC determination; ESBL screening and confirmatory testing by the methods of the Clinical and Laboratory Standards Institute (CLSI); and for isolates for which the MICs of extended-spectrum cephalosporins were ≥1 μg/ml or the MICs of cefpodoxime were >4 μg/ml, PCR amplification and sequencing of the ESBL and pAmpC genes. PCR was positive for 73/81 isolates (45 isolates with an ESBL gene alone, 24 isolates with a pAmpC gene alone, with 4 isolates with both genes). Compared to PCR, confirmatory testing by the CLSI method yielded a sensitivity and a specificity of 98.0 and 96.3%, respectively; there were six false-positive results and one false-negative result. No distinction in the MIC distribution was apparent between isolates with the ESBL gene and isolates with the pAmpC gene. A substantial percentage of the isolates with PCR-confirmed ESBL and/or pAmpC genes fell within the current CLSI susceptible category. For a ceftazidime, ceftriaxone, or cefotaxime MIC of ≥2 μg/ml, a dichotomy existed between isolates with and without ESBL and pAmpC genes in most cases. This suggests that the presence of the ESBL and the pAmpC enzymes may yield similar MICs of extended-spectrum cephalosporins, many of which fall within the current nonresistant categories. Lowering of the current CLSI breakpoints for cephalosporins appears to be warranted.

UR - http://www.scopus.com/inward/record.url?scp=68549132348&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=68549132348&partnerID=8YFLogxK

U2 - 10.1128/JCM.00508-09

DO - 10.1128/JCM.00508-09

M3 - Article

C2 - 19494061

AN - SCOPUS:68549132348

VL - 47

SP - 2419

EP - 2425

JO - Journal of Clinical Microbiology

JF - Journal of Clinical Microbiology

SN - 0095-1137

IS - 8

ER -