[Preliminary study of the antagonistic effects between fosfomycin and beta-lactams on Pseudomonas aeruginosa observed on the antibiogram].

Antagonism patterns between beta-lactams (BL) and fosfomycin (FOS) were observed in antibiotic assay by agar diffusion method against the most of Pseudomonas aeruginosa strains. This antagonism was confirmed by antibiotic assays made on Mueller-Hinton agar containing subinhibiting concentrations of FOS. FOS + BL combinations, studied on the strain of Pseudomonas aeruginosa ATCC 27853 by means of checker board method, exhibit antagonism of FOS concentrations below 1 mg/l on ceftriaxone, piperacillin, ticarcillin and, less strongly, on imipenem. These results suggest that in vivo combination FOS + BL dosages must avoid low concentrations of FOS at the site of infection.