Fosfomycin demonstrates excellent activity against MRSA resistant to other anti-MRSA drugs

U.S.A.: According to a study published in the Journal of Antimicrobial Chemotherapy, fosfomycin exhibited remarkable efficacy against MRSA as well as isolates with resistance to or diminished response to other anti-MRSA medications such vancomycin, daptomycin, and linezolid.

The rising rates of disease resistance and the scarcity of novel antibiotics to combat these pathogens are causing considerable concern. Fosfomycin is of great relevance in this context because of its efficacy against a variety of these bacteria.

Researchers of this study wanted to assess the efficacy of various combinations of antimicrobial drugs used in the treatment of severe Gram-positive infections, including isolates with reduced sensitivity or resistance to vancomycin, daptomycin, linezolid, and ceftaroline, against a collection of MRSA strains, including isolates.

The MICs of fosfomycin, vancomycin, daptomycin, linezolid, ceftaroline, and cefazolin were determined for this purpose using a technique called broth microdilution testing. Chequerboard broth microdilution testing was used to select isolates for additional assessments in order to ascertain the in vitro synergy between fosfomycin and certain antibacterial drugs. In tests, vancomycin, linezolid, daptomycin, ceftaroline, and cefazolin were combined with fosfomycin.

Key findings of the study:

• In comparison to 86% of VISA and 95% of daptomycin-resistant S. aureus (DRSA) strains, fosfomycin sustained activity against 100% of vancomycin-resistant S. aureus (VRSA) and linezolid-resistant S. aureus (LRSA) strains.
• All 18 isolates against the tested strains clearly indicated synergy when fosfomycin and ceftaroline were combined.
• Linezolid with fosfomycin was the second-most effective combo treatment and showed synergy in 16 of the 18 strains.
• Only 7 out of the 18 strains examined showed synergy between daptomycin and fosfomycin.
• Vancomycin showed no interaction in 6 of the 6 studied strains, while cefazolin showed synergy in 6 of the 6 tested strains.

Fosfomycin showed synergy with linezolid or daptomycin for all or most of the strains examined, noted the authors.

Therefore, these combinations may be clinically useful in treating individuals with severe MRSA infections, they concluded.

REFERENCE

Louis D Saravolatz, Joan Pawlak, In vitro activity of fosfomycin alone and in combination against Staphylococcus aureus with reduced susceptibility or resistance to methicillin, vancomycin, daptomycin or linezolid, Journal of Antimicrobial Chemotherapy, 2022;, dkac380, https://doi.org/10.1093/jac/dkac380