SECONDARY BACTERIAL INFECTION IN MICE 

 SUMMARY 



1. The LDgQ dose for mice of S. typhimurium, strain RIA, is 

 4.1 X 10^ cells per mouse for animals individually housed without 

 bedding and maintained at 25° C. It is 3.8 x 10 cells per mouse for 

 animals similarly housed but kept at 5° C. 



2, No effect of cold could be detected in mice infected with the 

 highly virulent SR-U strain of S. typhimurium since all animals died 

 following infection with only a few cells. Mice that were natural 

 carriers of salmonellae as judged by fecal discharge were highly 

 resistant to challenge and responded to cold in a manner similar to 

 normal mice infected with RIA, 



3. Strain RIA could be isolated from the tissues of infected ani- 

 mals with greater frequency and persisted longer in mice main- 

 tained at 5° C than those at 25° C, 



4. Staphylococci were isolated from livers of animals that sur- 

 vived salmonella infection for 14 days at 5° C and the incidence of 

 staphylococci was proportional to the number of salmonellae in- 

 jected. At 25° C, only a small percentage of mice had staphylococci 

 in tissues and these occurred independent of the infectious dose of 

 salmonellae. These observations were made on normal mice infected 

 with RIA and on carrier mice infected with SR-U. 



5. The feeding of 0.01 N hydrochloric acid to mice in lieu of 

 drinking water is apparently harmless to the general well-being of 

 the animals under the conditions indicated, but rids the gut of all 

 culturable staphylococci in five to seven days in experiments con- 

 ducted in the winter. The period of hydrochloric acid treatment must 

 be extended to achieve comparable results in summer studies. 

 Neither ridding the gut of the normally present coagulase- negative 

 staphylococci nor establishing a coagulase-positive strain by the 

 feeding of contaminated food altered the incidence of tissue invasion 

 by coagulase- negative organisms. 



6. Hydrochloric acid treatment failed to alter the incidence of 



291 



