Fig. 1. MBSA-MDP-mediated killing of Salmonella in vitro and in vivo. (A) J774E macrophages (1x10⁶ cells/well) were treated with the indicated concentrations of MBSA-MDP or free MDP for 12 hours. Treated macrophages were infected with Salmonella typhimurium (1x10⁷) as described in the Materials and Methods, and the infected cells were incubated in the respective drug-containing medium. After incubation for 12 hours at 37°C, the macrophages were lysed in solubilization buffer, and an aliquot of the cell lysates was used to determine the level of viable bacteria they contain (colony-forming units). Results are expressed as an average of three determinations±s.d. (B) To determine the efficacy of MBSA-MDP for treatment of Salmonella infection in vivo, C57B1-6 mice were infected with Salmonella as described in the Materials and Methods on day 0. Subsequently, Salmonella-infected animals received intraperitoneal injections of free MDP or MBSA-MDP (1 µg/mouse of MDP equivalent; 50 µg/kg body weight) or ciprofloxacin (1.4 mg/mouse; 70 mg/kg body weight) daily for four consecutive days. Finally, the splenic load of Salmonella was determined by measuring the colony forming units on day 10 as described in the Materials and Methods. Results are expressed as percentage survival of three independent experiments±s.e. The number of colonies in untreated control mice (2.21x10⁴ CFU±s.e.) was taken as 100%.