Antimicrobial therapy in experimental pseudomonas infection

Young adult mice were infected with recent clinical isolates of Pseudomonas aeruginosa (P.a.). The LD₅₀ in utreated mice was 6.7 X 10⁷ organisms for one strain (MS2) and 2.5 X 10⁷ organisms for the other (MZT624). Non infected injected controls all survived. Mortality in utreated controls was 73% (MS2) and 83% (MZT624). Treated animals received carbenicillin (CA), colistimethate (CO), gentamicin (GE) or polymyxin B (PB), either singly or in various combinations. MS2 infections were significantly ameliorated by CA or PB singly (53% and 40% mortality) and by several combinations (12.5% to 45% mortality). MZT624 infections were significantly altered by GE, GE plus PB, and by 2 3 drug regimens (29% to 43% mortality). In this model CA, GE, and PB were the most effective single anti P.a. agents; CA plus PB or GE, and GE plus PB were the most effective 2 drug combinations. No instances of in vivo synergism were observed.