In vitro susceptibilities of clinical isolates of ertapenem-non-susceptible Enterobacteriaceae to cefotaxime, ceftazidime, cefepime and aztreonam

Abstract

To investigate the in vitro susceptibility of ertapenem-non-susceptible Enterobacteriaceae (ENSE) isolates to cefotaxime, ceftazidime, cefepime and aztreonam. Clinical isolates of ENSE tested in this study were obtained from 10 major teaching hospitals in Taiwan during the period January 2008 to October 2010. MICs of ertapenem, cefotaxime, ceftazidime, cefepime and aztreonam were determined by the agar dilution method and were interpreted based on 2011 MIC interpretive criteria recommended by the CLSI and EUCAST. A total of 412 non-duplicate ENSE isolates (with ertapenem MIC values ≥ 0.5 mg/L) were tested. These comprised 72 isolates of Escherichia coli [28 (38.9%) were extended-spectrum β-lactamase (ESBL)-producing isolates], 167 isolates of Klebsiella pneumoniae [74 (44.3%) were ESBL-producing isolates], 115 isolates of Enterobacter cloacae, 13 isolates of Enterobacter aerogenes, 20 isolates of Citrobacter freundii and 25 isolates of Serratia marcescens. According to 2011 CLSI (EUCAST) MIC interpretive breakpoints for Enterobacteriaceae, 64% (31%) of all ENSE isolates, 45.8% (16.7%) of E. coli isolates, 53% (29.3%) of K. pneumoniae isolates and 86.1% (35.7%) of E. cloacae isolates were susceptible to cefepime. As for ESBL-producing ENSE isolates, 25% and 14.3% of E. coli isolates and 36.5% and 10.8% of K. pneumoniae isolates were susceptible to cefepime based on CLSI and EUCAST criteria, respectively. Cefepime exerts in vitro antimicrobial activity against a significant portion of clinical isolates of ENSE, although there are discrepancies between results obtained using the CLSI-2011 and EUCAST-2011 guidelines.