In vitro susceptibility to fosfomycin in clinical and environmental extended-spectrum beta-lactamase producing and/or ciprofloxacin-non-susceptible Escherichia coli isolates

Abstract

Extended-spectrum beta-lactamase producing and ciprofloxacin-non-susceptible Escherichia coli are clinical and environmental issues. We evaluated the susceptibility profile of fosfomycin in non-susceptible E. coli isolated from urine and the environment. We measured the activity of fosfomycin against 319 and 36 E. coli strains from urine and environmental isolates, respectively, collected from rivers. Fosfomycin resistance profiles were investigated using the minimal inhibitory concentration (MIC), according to the Clinical and Laboratory Standards Institute (CLSI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST) guidelines. Antibiotic susceptibility testing revealed that 5% and 6.6% of urine samples were non-susceptible to fosfomycin according to CLSI and EUCAST guidelines, respectively. The fosfomycin MIC50/90 was 0.5/4 mg/L. Of the 36 E. coli isolates from river water, 11.1% and 13,8% were non-susceptible to fosfomycin according to CLSI and EUCAST, respectively (range ≤0.25 ≥512 mg/L). All the isolates with MIC ≥512 mg/L for fosfomycin showed the fosA3 gene. Fosfomycin resistance was more frequent in the environment than in clinical samples.

Figure 1. Points of water collection in the main rivers of the six watersheds of Curitiba: 01) Passauna River, 02) Barigui River, 03) Belem River, 04) Atuba River, 05) Ribeirao dos Padilhas River, and 06) Iguacu River.

Figure 2. Detection and distribution of fosfomycin-resistant Escherichia coli according to sanitary districts (red dots) and rivers (yellow dots): 01) Passauna River, 02) Barigui River, 03) Belem River, 04) Atuba River, 05) Ribeirao dos Padilhas River, and 06) Iguacu River.

Figure 3. Isolates with MIC ≥ 512 mg/L for fosfomycin showing detection (A and B). Isolates with MIC values < 512 mg/L showed no gene amplification (C).