Antimicrobial agents active against carbapenem-resistant Escherichia coli and Klebsiella pneumoniae isolates in Lebanon.

INTRODUCTION:It is not yet clear which antimicrobial agents should be used to treat the ominously increasing infections with carbapenem-resistant (CR) bacteria. We therefore investigated the activity of different antimicrobial agents against CR Escherichia coli and Klebsiella pneumoniae in Lebanon. METHODOLOGY:This retrospective study assessed the minimum inhibitory concentrations (MICs) of three carbapenems (by Etest), as well as the in vitro activity of eight other antimicrobials (by disk diffusion) against CR E. coli (n = 300) and K. pneumoniae (n = 232) isolates recovered at a major University Medical Center in Lebanon. RESULTS:Higher percentages of isolates showing carbapenem MICs of ≤ 8 µg/mL were noted among the CR E. coli compared to the CR K. pneumoniae for ertapenem (48% vs 27%), imipenem (74 % vs 58%) and meropenem (82% vs 63%). Among the eight other antimicrobials, activity was generally higher when the MICs for the three carbapenems were ≤ 8 µg/mL. Regardless of the MIC level of the three carbapenems, very low susceptibility rates (≤ 33%) were noted for ciprofloxacin, trimethoprim-sulfamethoxazole and aztreonam against both E. coli and K. pneumoniae isolates. With Amikacin, higher susceptibility rates were seen against E. coli isolates (81%-97%) than against K. pneumoniae isolates (55%-86%), also reflecting higher activity than gentamicin (44%-54%). The best activity (66%-100%) was observed for tigecycline, colistin and fosfomycin against both CR species. CONCLUSIONS:Based on the in vitro findings in this study, the combination of a carbapenem showing an MIC of ≤ 8 µg/mL together with an active colistin, tigecycline, or fosfomycin, would offer a promising treatment option for patients infected with CR E. coli or K. pneumoniae.