Antimicrobial susceptibilities of urinary extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae to fosfomycin and nitrofurantoin in a teaching hospital in Taiwan.

BACKGROUND: Urinary tract infections (UTIs) caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae have become clinical problems because of limited therapeutic options. The role of fosfomycin in the era of growing bacteria resistance has been widely discussed recently. In this study, we aimed to know the local antimicrobial susceptibilities, fosfomycin susceptibility in particular, of urinary ESBL-producing E coli and K pneumoniae isolates in Taiwan.

METHODS: We collected 200 urine isolates, including 134 ESBL-producing E coli (ESBL-EC) and 66 ESBL-producing K pneumoniae (ESBL-KP) isolates from July 2008 to December 2009 in a university-affiliated teaching hospital in Taiwan. We used disk diffusion method to determine susceptibility to fosfomycin. Fosfomycin may have lower susceptibility when using disk diffusion method compared with agar dilution method. Broth microdilution test was also used to determine minimal inhibitory concentrations (MICs) and susceptibilities to other antimicrobial agents.

RESULTS: Imipenem was active against ESBL-EC and ESBL-KP. Fosfomycin had good susceptibility to ESBL-EC (95.5%), including in hospital-acquired isolates, but lower antimicrobial activity against ESBL-KP (57.6%). Trimethoprim-sulfamethoxazole had the highest resistance rate to ESBL-EC and ESBL-KP. Comparing with non-hospital-acquired isolates, hospital-acquired ESBL-KP was associated with significantly lower susceptibility of gentamicin (13.3% vs. 66.7%), trimethoprim-sulfamethoxazole (8.9% vs. 38.1%), ciprofloxacin (26.7% vs. 61.9%), and amikacin (46.1% vs. 81.0%) (p<0.05). The resistance of some strains to ciprofloxacin was significantly associated with lower susceptibilities of gentamicin (32.6% in ESBL-EC), nitrofurantoin (2.4% in ESBL-KP) and trimethoprim-sulfamethoxazole (9.8% in ESBL-KP) (p<0.05) but not accompanied with decreasing susceptibility of fosfomycin.

CONCLUSION: Fosfomycin had the excellent activity against ESBL-EC but not ESBL-KP in this study. Based on the study findings, we suggest that fosfomycin can be a therapeutic option for UTIs with ESBL-EC. Nitrofuranoin was actively against ESBL-EC. Nitrofurantoin may be an alternative option for uncomplicated UTIs with ESBL-EC in Taiwan.