In vitro susceptibility of fosfomycin against Extended-Spectrum β-lactamase-producing Escherichia coli isolated from urine specimens

Na Wu, Bai Yi Chen, Su Fei Tian and Yun Zhuo Chu

Background: The production of extended-spectrum β-lactamases (ESBLs) brings challenge to the treatment of urinary infection caused by Escherichia coli with increasing resistance to common antibiotics. For the limited treatment option, fosfomycin as traditional antibiotic has been reevaluated. Yet there are scarce studies regarding the antibacterial activity of fosfomycin for urinary infection in China. With this regard, we investigated in vitro susceptibility of fosfomycin and other 7 agents against ESBLs-producing Escherichia coli isolated from urine specimens.

Methods: The minimum inhibitory concentrations (MICs) of fosfomycin and other comparative agents including meropenem, piperacillin-tazobactam, amikacin, cefepime, cefotaxime, ceftazidime and levofloxacin were determined by agar dilution method recommended by the Clinical Laboratory Standards Institute (CLSI) 2010.

Results: Of the 100 strains isolated from urine, none was found resistant to meropenem .The relatively high susceptibility was found to piperacillin-tazobactam (94%), amikacin (85%), fosfomycin (82%) and cefepime (60%). The susceptibility rate of fosfomycin did not differ significantly between the cefotaxime-resistant (CTX-R) and cefotaxime-susceptible (CTX-S) group (80.1% vs 84.6%, P=0.712), ceftazidime-resistant (CAZ-R) and ceftazidime-susceptible (CAZ-S) group (78.1% vs 84.8%, P=0.552), levofloxacin-resistant (LVX-R) and levofloxacin-susceptible (LVX-S) group (85.4% vs 62.5%, P=0.07) respectively.

Conclusions: For the relatively high antibacterial activity in vitro against ESBLs-producing Escherichia coli isolated from urine specimens and the non-influenced by the pattern of resistance to other antimicrobials, fosfomycin is of great clinical value in the treatment of uncomplicated urinary infection caused by ESBLs-producing Escherichia coli.