Protective and therapeutic efficacy of Lactobacillus casei against experimental murine infections due to Mycobacterium fortuitum complex.

A bacterial immunopotentiator, LC 9018 (heat-killed Lactobacillus casei), was studied for its protective and therapeutic efficacies against Mycobacterium fortuitum and M. chelonae infections in mice. This agent reduced the incidence of spinning disease and gross renal lesions and enhanced the elimination of organisms at the site of infection in the host mice, when administered intramuscularly six times a week (0.1 mg dry weight per injection, one injection on each day of treatment) from 1 week before to 2 weeks after infection. The LC 9018 injections in this protocol caused a marked increase in the phagocytic function, O2- -producing ability and chemiluminescence of host peritoneal macrophages. Moreover, LC 9018 injections using the same schedule resulted in an enhancement of interleukin-1-producing function of the macrophages, particularly in the infected mice. These findings indicate that LC 9018 administration with the present protocol can activate macrophage functions, in particular those related to microbicidal activity. This would partly explain the protective and therapeutic efficacy of LC 9018 against infection due to M. fortuitum complex.