A continuous oral administration of antibiotics, mostly chloramphenicol, in combination with resistancelowering agents, such as carbon tetrachloride, cortisone acetate and croton oil, was very effective in establishing infections in mice when they were challenged with resistant strains of Shigella 2b and 3a. The inoculated organisms remained in the intestinal tract for about a week in most of the animals and for as long as 4 or 5 weeks in a few. Pathologic examination revealed that lesions developed in various organs, especially the intestinal tract, showing acute or chronic colitis.
Infection was not induced in animals which were administered sensitive strains; in most of the mice injected with the sensitive strain, no organisms could be found in their feces after 1 or 2 days. The absence of organisms in the feces may be attributed to the difference in treatment of mice with antibiotics; the antibiotic was administered for 2 or 3 days and stopped one day prior to the inoculation of organisms.
Thus, the elimination of intestinal microbial flora with the aid of antibiotics is primarily significant in establishing Shigella infection in mice and that the resistance-lowering agents seem to play a secondary role, in accelerating the infection.
Differences in the serotype of Shigella (2b and 3a) and in the sex (male and female) and strains (dd and CFW) of mice did not seem to influence the grade or course of infections as far as the results obtained were concerned.