title: Evaluation of a new cefepime-clavulanate ESBL Etest to detect extended-spectrum beta-lactamases in an Enterobacteriaceae strain collection.
abstract: OBJECTIVE
  In this study, we evaluated the performance of a new ESBL Etest configuration based on clavulanate synergy with cefepime compared with cefotaxime-clavulanate and ceftazidime-clavulanate ESBL Etest strips for the detection of extended-spectrum beta-lactamases (ESBL) in an Enterobacteriaceae strain collection, with special focus on Enterobacter spp.
  
  
  METHODS
  Overall, a total of 54 clinical isolates of ESBL-producing Enterobacteriaceae species were evaluated: Enterobacter aerogenes (n=3), Enterobacter cloacae (n=10), Escherichia coli (n=10), Klebsiella oxytoca (n=3), Klebsiella pneumoniae (n=25) and Proteus mirabilis (n=3). To check Etest behaviour with resistance phenotypes similar to ESBL, our panel was expanded by six clinical isolates of K. oxytoca that were identified as putative producers of their chromosomal K1 beta-lactamase.
  
  
  RESULTS
  With this panel, ESBL Etest was 98% sensitive with cefepime-clavulanate, 83% with cefotaxime-clavulanate, and 74% with ceftazidime-clavulanate strips. Concentrating on Enterobacter spp., reliable ESBL detection could only be achieved by the new cefepime-clavulanate strip since it confirmed ESBL production in all strains (100% sensitivity) whereas only 4/13 (31%) of Enterobacter strains were positive using cefotaxime-clavulanate or ceftazidime-clavulanate strips. A limitation of using the new cefepime strip was less than optimal specificity with K1 phenotypes of K. oxytoca: among six strains, four isolates were scored false-positive by Etest strips containing cefepime-clavulanate.
  
  
  CONCLUSIONS
  The new Etest ESBL strip containing cefepime-clavulanate is a valuable supplement to current methods for detection of ESBLs. In our study collection, the cefepime-clavulanate strip was the best configuration for detection of ESBLs, particularly in Enterobacter spp.
authors.affiliation: Institut für Infektionsmedizin, Zentrum für Klinisch-Theoretische Medizin I, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany. e.stuerenburg@uke.uni-hamburg.de
authors.forename: Enno
authors.initials: E
authors.lastname: Stürenburg
authors.forename: Ingo
authors.initials: I
authors.lastname: Sobottka
authors.forename: Djahesh
authors.initials: D
authors.lastname: Noor
authors.forename: Rainer
authors.initials: R
authors.lastname: Laufs
authors.forename: Dietrich
authors.initials: D
authors.lastname: Mack
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000077723:Cefepime; D002511:Cephalosporins / Q000494:pharmacology*; D019818:Clavulanic Acid / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004754:Enterobacter / Q000187:drug effects / Q000201:enzymology; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000201:enzymology*; D004756:Enterobacteriaceae Infections / Q000382:microbiology; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D041121:Klebsiella oxytoca / Q000187:drug effects; D010641:Phenotype; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid; D000077723:Cefepime; D001618:beta-Lactamases