Evaluation of The Clinical and Laboratory Standards Institute (CLSI) Phenotypic Confirmatory Test to Detect the Presence of Extended-Spectrum Beta-lactamases (ESBL) from 4,005 Escherichia coli, Klebsiella oxytoca, Klebsiella pneumonia and Proteus mirabilis.

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Evaluation of The Clinical and Laboratory Standards Institute (CLSI) Phenotypic Confirmatory Test to Detect the Presence of Extended-Spectrum Beta-lactamases (ESBL) from 4,005 Escherichia coli, Klebsiella oxytoca, Klebsiella pneumonia and Proteus mirabilis.

J Med Microbiol. 2014 Jan 29;

Authors: Morrissey I, Bouchillon SK, Hackel M, Biedenbach DJ, Hawser SP, Hoban D, Badal RE

Abstract
A sub-set of Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae and Proteus mirabilis collected for the Study for Monitoring Antimicrobial Resistance Trends (SMART) that were positive for the CLSI extended-spectrum beta-lactamase (ESBL) phenotypic confirmatory test (N=3,245) or had an ertapenem MIC of ≥0.5μg/ml (N=293) or both (N=467) were analyzed for ESBL genes. Most ESBL phenotype E. coli or K. pneumoniae possessed an ESBL gene (95.8% & 88.4%, respectively) or 93.1% if carbapenem non-susceptible K. pneumoniae were removed. This rate was lower for P. mirabilis (73.4%) and K. oxytoca (62.5%). Virtually all ESBL-positive isolates (99.5%) were cefotaxime non-susceptible (CLSI or EUCAST breakpoints). Fewer (82%) were ceftazidime non-susceptible (CLSI breakpoints). Also 21.1% of E. coli, 25% of K. oxytoca and 78.7% of P. mirabilis were ceftazidime-susceptible but ESBL-positive. This suggests CLSI breakpoints for ceftazidime are too high to detect ESBLs. The lower EUCAST breakpoints detected ESBLs in E. coli and K. oxytoca better, but 59.6% of ESBL-positive isolates of P. mirabilis were ceftazidime-susceptible. For isolates with ertapenem MIC ≥ 0.5μg/ml, more accurate ESBL phenotype analysis was observed for E. coli and K. pneumoniae (sensitivity >95% for both, specificity 94.4% and 54.1%, respectively). If carbapenemase-positive K. pneumoniae were excluded specificity increased to 78%. The positive predictive values for the ESBL phenotypic test with E. coli and K. pneumoniae were 97.6% and 81.8%, respectively and negative predictive values were 75.9% and 95.2%, respectively. We therefore suggest it would be prudent to confirm phenotypic ESBL-positive P. mirabilis, K. pneumoniae and K. oxytoca with molecular analysis.

PMID: 24478449 [PubMed - as supplied by publisher]