Use of the cefepime-clavulanate ESBL Etest for detection of extended-spectrum beta-lactamases in AmpC co-producing bacteria.
BACKGROUND
Extended-spectrum beta-lactamases (ESBLs) may not always be detected in routine susceptibility tests. This study reports the performance of the cefepime-clavulanate ESBL Etest for the detection of ESBLs in Enterobacteriaceae, including those producing AmpC enzyme.


METHODS
Consecutive non-duplicate isolates of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolated from bloodstream infections from January to June 2008 were tested for ESBL by both the standard CLSI double-disk diffusion method using ceftazidime and cefotaxime disks and Etests using ceftazidime/ceftazidime-clavulanate, cefotaxime/cefotaxime-clavulanate and cefepime/cefepime-clavulanate gradients. Isolates were also tested for the presence of transferable AmpC beta-lactamase by AmpC disk test and the efficacies of the different Etests in detecting ESBL production were compared.


RESULTS
A total of 113 bacterial isolates (61 K. pneumoniae, 50 E. coli, and 2 P. mirabilis) were recovered. Respectively, 42 (37.2%) and 55 (48.7%) isolates were positive for ESBL by the ceftazidime-clavulanate and cefotaxime-clavulanate combined disk tests. The cefepime/cefepime-clavulanate Etest strip detected the maximum number of isolates (70/113, 61.9 %) as ESBL-positive compared to the ceftazidime/ceftazidime-clavulanate and cefotaxime/cefotaxime-clavulanate strips, which detected 57 (50.4%) isolates each as ESBL-positive. All three ESBL Etest strips were equally effective in detecting ESBL in the isolates that were AmpC negative. In the 66 (58.4%) isolates that co-produced AmpC in addition to the ESBL enzymes, cefepime/cefepime-clavulanate Etest strip detected ESBL in an additional 13 (11.4%) isolates as compared to the other ESBL Etest strips.


CONCLUSIONS
Cefepime-clavulanate ESBL Etest is a suitable substitute to test for ESBL production, especially in organisms producing AmpC beta-lactamases.
Department of Microbiology, VMMC and Safdarjung Hospital, New Delhi-110029, India. srujana_micro@yahoo.co.in
Srujana
S
Mohanty
Rajni
R
Gaind
Rajeev
R
Ranjan
Monorama
M
Deb
D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000032:analysis / Q000096:biosynthesis*; D000077723:Cefepime; D002439:Cefotaxime / Q000494:pharmacology / Q000627:therapeutic use; D002442:Ceftazidime / Q000494:pharmacology / Q000627:therapeutic use; D002511:Cephalosporins / Q000494:pharmacology* / Q000627:therapeutic use; D019818:Clavulanic Acid / Q000494:pharmacology* / Q000627:therapeutic use; D024901:Drug Resistance, Multiple, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000378:metabolism*; D004756:Enterobacteriaceae Infections / Q000188:drug therapy / Q000378:metabolism / Q000382:microbiology*; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000378:metabolism; D008826:Microbial Sensitivity Tests / Q000379:methods*; D011513:Proteus mirabilis / Q000187:drug effects / Q000378:metabolism; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000032:analysis / Q000096:biosynthesis*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D019818:Clavulanic Acid; D000077723:Cefepime; D002442:Ceftazidime; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; D002439:Cefotaxime