Fosfomycin: In vitro efficacy against multidrug-resistant isolates beyond urinary isolates

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Fosfomycin (FOF) is a bactericidal antimicrobial effective against Gram-negative bacteria, including multidrug-resistant (MDR) and metallo-β-lactamase (MBL)-producing Enterobacteriaceae.
• Limited data exist on FOF's efficacy beyond urinary tract infections (UTIs).

Purpose of the Study:

• To analyze FOF susceptibility rates among MDR Enterobacteriaceae isolates.
• To evaluate FOF's potential as an alternative treatment for non-UTI infections caused by resistant Gram-negative bacteria.

Main Methods:

• Susceptibility testing of 290 MDR Enterobacteriaceae isolates using gradient, disk diffusion, and agar dilution methods.
• Determination of imipenem (IPM) minimum inhibitory concentrations (MICs) and MBL production using gradient tests.

Main Results:

• 20.7% of extended-spectrum β-lactamase (ESBL)-positive isolates were resistant to FOF, with higher rates in Klebsiella spp. (35.7%) and Morganella spp. (50.0%).
• FOF demonstrated good in vitro activity against blood (86.9%) and genitourinary (91.7%) isolates.
• Significant resistance to FOF was observed in extensively drug-resistant (72.2%) and carbapenem-resistant (61.1%) isolates.

Conclusions:

• Fosfomycin exhibits good activity against carbapenem-resistant isolates, suggesting potential for non-UTI infections.
• Caution is recommended when using FOF for infections involving ESBL-producing Klebsiella spp.
• Further clinical trials are needed to confirm FOF's efficacy in various infection types beyond UTIs.