title: Genetic instability of R plasmids in relation to the shift of drug resistance patterns in Salmonella johannesburg.
abstract: Observation of the resistance of Salmonella johannesburg to the six drugs ampicillin (A), streptomycin (S), tetracycline (T), chloramphenicol (C), kanamycin(K) and sulphadiazine (Su) was made over the 7 years from 1973 to 1979. Strains with ASTCKSu- and ASCKSu- resistance patterns predominated in the years 1973-1975 and 1976-1979, respectively. These resistances were found to be mediated by autotransferring plasmids belonging to the incompatibility group FIme. The ASTCKSu-resistance plasmids were unstable, giving rise to deletion variants at a much higher frequency than ASCKSu-resistance plasmids either of natural origin or derived in vitro from the ASTCKSu-resistance plasmids. Thus, the ASCKSu-resistance plasmid might be a deletion variant of the ASTCKSu-resistance plasmid. This is supported by the extensive similarity of their cleavage patterns produced by specific restriction endonucleases.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002701:Chloramphenicol / Q000494:pharmacology; D004262:DNA Restriction Enzymes; D007612:Kanamycin / Q000494:pharmacology; D009154:Mutation; D011815:R Factors; D012475:Salmonella / Q000187:drug effects / Q000235:genetics*; D013307:Streptomycin / Q000494:pharmacology; D013411:Sulfadiazine / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D013411:Sulfadiazine; D007612:Kanamycin; D002701:Chloramphenicol; D000667:Ampicillin; D004262:DNA Restriction Enzymes; D013752:Tetracycline; D013307:Streptomycin