Abstract
1. The development of rifampicin-resistant (RFPr) mutants of Salmonella typhimurium LT-2 and Staphylococcus aureus 209P showed to be of streptomycin type.
2. The frequencies of development of one-step high RFPr mutants were about 10-8 in LT-2 and about 10-7 in 209P.
3. Mutation to one-step high RFPr mutants in LT-2 was induced by ultraviolet irradiation (UV). The RFPr mutation was regarded as recessive, because of the presence of a long lag required for the phenotypic expression.
4. One-step high RFPr mutants were rather unstable genetically in both LT-2 and 209P.
5. The one-step high RFPr mutants used in the present study were assumed not to have been developed due to the reduced permeability to RFP, because their resistance was not affected by EDTA. EDTA did not appreciably influence the detection of one-step high RFPr mutants of LT-2 induced by UV.
6. The one-step high RFPr mutants of LT-2 and 209P showed reduced growth rates, as compared with the wild type strains.
7. The one-step high RFPr mutants of LT-2 and 209P were less virulent to mice than the wild type strains.
8. The one-step high RFPr mutants of 209P produced less α-hemolysin, less coagulase, and less yellow, pigment than the wild type strain.
