Antibacterial activity of fosmidomycin on chromosomic and plasmid-determined fosfomycin-resistant strains.

The antibacterial activity of fosmidomycin (Fm) on chromosomic and plasmid-determined fosfomycin-resistant (For) strains of Gram-negative bacteria was studied. Presence of For-plasmids did not protect host bacteria from the antibiotic effect of Fm. In clinical isolates Fm was more active than Fo in 67% of the strains whereas Fo was more active for only 2%; 76% of the strains showed cross resistance to both antibiotics. The Fmr character was not transferred by conjugation. For mutants selected in the hospital environment as well as in the laboratory did not always show cross resistance with Fm, and the alterations in the transport systems of both antibiotics were not the only mechanism of cross resistance.