In vitro susceptibility and distribution of beta-lactamases in Enterobacteriaceae causing intra-abdominal infections in North America 2010–2011

The Study for Monitoring Antimicrobial Resistance Trends has been monitoring the activity of antimicrobials indicated for the treatment of intra-abdominal infections since 2004. This report documents the in vitro activity of several recommended antimicrobials against 3449 gram-negative bacilli isolated from the 30 and 25 participating sites in North America in 2010–2011, respectively, and characterizes the extended-spectrum beta-lactamases (ESBL) identified in ESBL-positive and ertapenem-non-susceptible isolates of Enterobacteriaceae. Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Proteus mirabilis, Klebsiella oxytoca, Citrobacter freundii, Enterobacter aerogenes, Serratia marcescens, and Morganella morgannii were the most common species isolated. The incidence of beta-lactamase production was 8.8% and 8.9% for E. coli and K. pneumoniae, respectively. Overall the most active antimicrobials were amikacin, piperacillin-tazobactam, imipenem, and ertapenem, although beta-lactamase production reduced the activity of most agents. Characterization of beta-lactamase genes determined that blaSHV, blaCTX-M, blaAmpC, and blaKPC were commonly found in most beta-lactamase–positive isolates.