Synergistic effects of romurtide and cefmenoxime against experimental Klebsiella pneumonia in mice.

We investigated the synergistic effects of romurtide (MDP-Lys [L18]) and cefmenoxime (CMX) in the treatment of experimental Klebsiella pneumonia in mice. Mice were infected with 1 x 10(4) CFU of Klebsiella pneumoniae by inhalation of aerosol bacterial suspension. About 90% of untreated animals died within a week; however, the mortality rate of animals treated with CMX alone at a dose of 40 mg/kg/day was 60% at 7 days after the infection. When one or two doses of L18 were administered before or after the infection concomitantly with CMX, a remarkable improvement in the survival rate was observed. There was no significant improvement in the survival rate of animals treated with L18 alone before or after infection. Histopathological sections of the lungs of mice treated with CMX and L18 showed slower progression of infection than those of mice treated with CMX alone. Significant differences were also found in quantitative cultures of viable bacteria in the lungs 1 to 4 days after the infection. Although viable bacterial counts in the lungs of the control and CMX-treated groups showed a rapid increase 24 to 48 h after the infection, they remained lower than the initial counts (x 10(4)) in the lungs of mice treated with combination regimens. From these results, it can be concluded that L18 is a useful biological response modifier in the treatment of acute pulmonary bacterial infections.