In-vitro susceptibility of quinolone-resistant clinical isolates of Escherichia coli to fosfomycin trometamol.

Escherichia coli (E. coli) is the most commonly isolated microorganism in uncomplicated lower urinary tract infections (UTI). Due to the increased isolation of E. coli strains resistant to quinolones, it is important to have available alternative drugs to this class of antibiotics as therapy for UTIs caused by this pathogen. Among the large number of currently available antimicrobial agents, fosfomycin trometamol is a useful alternative due to its peculiar microbiological and pharmacokinetic properties. Therefore, we tested the in vitro susceptibility of 79 quinolone-resistant clinical urinary isolates of E. coli to fosfomycin trometamol in comparison with amoxicillin, chloramphenicol, cotrimoxazole, netilmicin, nitrofurantoin and tetracycline. Fosfomycin trometamol showed high activity with a MIC90 of 4 mg/l. While no strains were resistant to fosfomycin trometamol, 83.5%, 63.3%, 58.2%, and 48.1% of the isolates were resistant to tetracycline, amoxicillin, chloramphenicol and cotrimoxazole, respectively. Nitrofurantoin and netilmicin resistance was present only in 12.7% and 6.3% of the strains, respectively. In conclusion, fosfomycin trometamol has retained its activity against quinolone-resistant strains of E. coli and cross-resistance with other classes of antimicrobial agents is not presently a problem. The strains tested did present high levels of resistance to other classes of antibiotics.