title: Genetic stability of various resistance factors in Escherichia coli and Salmonella typhimurium.
abstract: Genetic stability of R factors was studied in Salmonella typhimurium LT-2 and Escherichia coli K-12. It was found that fi(+) R [or R(f)] factors were unstable in LT-2, losing their drug-resistance markers at high frequencies, and were stable in K-12; fi(-) R [or R(i)] factors were stable in both hosts. Both fi(+) and fi(-) R factors were genetically stable also in recombination-deficient mutants of K-12. An fi(+) R factor, which was unstable in S. typhimurium LT-2 wild type, was relatively stable in a recombination-deficient mutant of LT-2. In the spontaneous loss of the drug-resistance markers of fi(+) R factors in LT-2, the markers for sulfanilamide, streptomycin, and chloramphenicol resistance were lost together at high frequencies and the tetracycline marker was retained stably. The remaining drug-resistance markers of the spontaneous segregants of LT-2 were transmissible to K-12 by mixed cultivation, indicating that they were still in the form of R factors.
mesh_terms: D001431:Bacteriological Techniques; D002701:Chloramphenicol / Q000494:pharmacology; D003470:Culture Media; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects*; D005827:Genetics, Microbial; D009154:Mutation; D011995:Recombination, Genetic; D012486:Salmonella typhimurium / Q000187:drug effects*; D013307:Streptomycin / Q000494:pharmacology; D013424:Sulfanilamides / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D003470:Culture Media; D013424:Sulfanilamides; D002701:Chloramphenicol; D013752:Tetracycline; D013307:Streptomycin