Topic:

Antibiotic resistance

Abstract No.:

ISE.091

Title:

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

Author(s):

P.-R. Hsueh; National Taiwan University Hospital, Laboratory Medicine and Internal Medicine, Taipei/TW

Abstract:

Background: To investigate the in vitro susceptibility of ertapenem-nonsusceptible Enterobacteriaceae (ENSE) isolates to cefotaxime, ceftazidime, cefepime, and aztreonam.
Methods: Clinical isolates of ENSE tested in this study were obtained from ten major teaching hospitals in Taiwan during the period January 2008 to October 2010. MICs of five antimicrobial agents (ertapenem, cefotaxime, ceftazidime, aztreonam, and cefepime) were determined by the agar dilution method and were interpreted based on current (2011) minimum inhibitory concentration (MIC) interpretive criteria recommended by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST).
Results: A total of 412 non-duplicate ENSE isolates (with ertapenem MIC values ³0.5 mg/L) were tested. These isolates comprised 72 isolates of Escherichia coli (28 [38.9%] were extended-spectrum β-lactamase [EBSL]-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 current 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. Among the ENSE isolates with ertapenem MIC values ³ 1 mg/L (n=277), 57.8% (15.6%) of E. coli, 46.4% (22.3%) of K. pneumoniae, and 82.6% (31.4%) of E. cloacae isolates were also susceptible to cefepime according to CLSI (EUCAST) criteria. As for ESBL-producing ENSE isolates, 25.0% 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.
Conclusion: Cefepime exerts in vitro antimicrobial activity against a significant portion of clinical isolates of ENSE and the susceptibility rate differs depending on the criteria applied. Whether the use of cefepime for the treatment of infections caused by ENSE is appropriate requires further clinical investigation.