Prevalence of extended-spectrum beta-lactamases in Enterobacter cloacae in Taiwan and comparison of 3 phenotypic confirmatory methods for detecting extended-spectrum beta-lactamase production.

BACKGROUND AND PURPOSE: The prevalence of extended-spectrum beta-lactamases (ESBLs) in Enterobacter cloacae remains unclear in Taiwan. This study was conducted to investigate the prevalence of ESBL-producing E. cloacae in Taiwan.

METHODS: 116 clinical isolates of E. cloacae were tested for cefepime susceptibility. Isolates with a minimal inhibitory concentration (MIC) of > or = 0.25 microg/mL for cefepime were tested for the ESBL phenotype by the combination-disk synergy tests (CDSTs) using cefotaxime and ceftazidime alone or in combination with clavulanic acid, the ESBL Etest using cefepime with or without clavulanic acid, and the double-disk synergy test (DDST) using cefepime and amoxicillin-clavulanate.

RESULTS: Thirty eight isolates had an MIC of > or = 0.25 microg/mL for cefepime. Of these, 27 had an ESBL phenotype; 24 were determined by DDST, 25 by CDST, and 21 by ESBL Etest. ESBL genes were identified in 24 isolates. One isolate without an ESBL phenotype but with an MIC of > or = 0.25 microg/mL for cefepime was confirmed to have the ESBL gene. DDST, CDSTs, and ESBL Etest detected 24, 22, and 21 of 25 isolates with the ESBL genotype, respectively. DDST had the highest sensitivity of 96.0% for detecting ESBLs among isolates and a specificity of 69.2%. CDSTs and ESBL Etest had sensitivities of 88.0% and 84.0%, respectively, and specificities of 69.2% and 100%, respectively. The overall prevalence of ESBL-producing E. cloacae was 21.6%.

CONCLUSIONS: A combination of DDST using cefepime and amoxicillin-clavulanate and CDSTs using cefotaxime and ceftazidime alone or in combination with clavulanic acid enhance the detection of ESBL production in Taiwan.