Antimicrobial therapy in experimental pseudomonas infection. II

Young adult male mice were infected with recent clinical isolates of Pseudomonas aeruginosa in an experimental model of lethal pseudomonas infection. Three strains of pseudomonas, designated MS2, MZT624 and 017 were inoculated intraperitoneally to initiate infection. Mortality in untreated control animals ranged from 71 to 88%. Treated animals received carbenicillin, gentamicin, polymyxin B, and colistimethate, either singly or in various combinations. No combination of antimicrobial agents was significantly more effective than an appropriate single drug in reducing mortality in MS2 and 017 infections. MZT624 infection did not respond to single drug therapy but mortality was significantly ameliorated with the use of one 2 drug combination and two 3 drug combinations. No true in vivo synergism was observed. In several instances, an organism showed an in vitro susceptibility to an antimicrobial agent that failed to prove therapeutically effective in vivo.