Evaluation of the in vitro activity of fosfomycin tromethamine against Gram-negative bacterial strains recovered from community- and hospital-acquired urinary tract infections in Turkey

Objectives: The aim of this study was to evaluate the in vitro activities of antimicrobial agents including fosfomycin tromethamine against Gram-negative isolates recovered from urine samples. Methods: A total of 2334 strains (1562 Escherichia coli, 509 Klebsiella spp, 85 Proteus spp, 75 Pseudomonas spp, 45 Enterobacter spp, 37 Acinetobacter baumannii, 8 Citrobacter spp, 7 Morganella morganii, and 6 Serratia spp) were identified by VITEK 2 during the study period, November 2008 to June 2012. Antimicrobial susceptibilities of the strains were also evaluated using the Kirby-Bauer disk diffusion method, in accordance with the Clinical and Laboratory Standards Institute guidelines. Results: Overall, 2160 (92.5%) of the isolates tested were susceptible to fosfomycin tromethamine. Higher resistance rates were observed among inpatients compared to outpatients. Resistance rates by strain were: 2.0% for E. coli, 4.4% for Enterobacter spp, 6.9% for Klebsiella spp, 9.4% for Proteus spp, 48.6% for A. baumannii, 56.0% for Pseudomonas spp, and 100% for Morganella morganii. All Serratia spp and Citrobacter spp strains were susceptible. Extended-spectrum beta-lactamase (ESBL)-producing isolates displayed higher fosfomycin resistance rates than negative strains (19.2% vs. 2.9%). The highest in vitro activity was detected for amikacin, piperacillin-tazobactam, and imipenem for all strains including ESBL-producers. Conclusions: Regardless of ESBL production, the excellent activity of fosfomycin against E. coli, Enterobacter spp, Serratia spp, and Citrobacter spp, indicates that the drug is a valuable therapeutic option for urinary tract infections, even those with co-trimoxazole- and ciprofloxacin-resistant isolates, but not in ESBL-producing Klebsiella spp, Pseudomonas spp, A. baumannii, and Proteus spp. Further studies should be carried out to determine the in vivo drug activity among Enterobacteriaceae other than E. coli. (C) 2013 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.