Effect of sensitization with Propionibacterium acnes on the growth of Listeria monocytogenes and Treponema pallidum in rabbits.

Sensitization of rabbits with Propionibacterium acnes, a nonspecific stimulant of the reticuloendothelial system, was investigated as a means of enhancing resistance to Treponema pallidum. A single i.v. dose of P. acnes given 3 or 7 days before challenge with Listeria monocytogenes was capable of suppressing the growth of the heterologous organism, whereas a single i.v. dose 24 hr or 14 days before challenge was not. Reactivation via i.v. elicitation with P. acnes 14 days after sensitization (1 day before challenge) caused significant suppression of listerial growth in the major organs 30 hr after i.v. challenge. A series of similar experiments was designed with T. pallidum as the challenge organism. Sensitization and repetitive elicitation with P. acnes did not change the time of appearance or progression of syphilitic chancres after i.v or i.d. challenge. Injection of P. acnes into sites of intradermal T. pallidum challenge in previously sensitized rabbits also failed to alter the evolution of syphilitic lesions. These results suggest that macrophage activation does not alter the host's ability to suppress the growth of T. pallidum.