Murine model for therapy of listeriosis in the compromised host. III. The effect of rifampicin.

10 different strains of Listeria monocytogenes tested in vitro were found to be susceptible to rifampicin showing minimal inhibitory concentrations between 0.0075 and 0.06 microgram/ml. Mice infected with a virulent strain of L. monocytogenes were treated with this antibiotic. Bacterial counts rapidly declined. In dextran sulfate-treated animals, deprived of their macrophage system and consequently highly susceptible to Listeria infection, rifampicin was able to protect the animals. Furthermore, nude athymic mice, chronically infected with L. monocytogenes, were also nearly cured. A few remaining bacteria, however, started to multiply after cessation of therapy, so that a relapse was noted. Development of resistance of L. monocytogenes to rifampicin during treatment was not observed.