[The plasmid profile of Salmonella typhimurium strains untypable by phages]

The authors examined 250 strains of Salmonella typhimurium, untypable by phagi, for the sensitivity to antibacterial substances and lysogeny. Testing of the sensitivity to a set of 13 antibacterial substances revealed that 157 strains (63%) were polyresistent. Most frequently they were resistent to ampicillin (96% strains), sulphamethoxydine (71.2%), carbenicillin (68% strains), tetracycline (56% strains), cephalotine (56%), chloramphenicol (53%) and septrin (51% strains). The presence of a prophage was revealed in 99.2% strains. In a narrower selection of 54 strains plasmid DNA was isolated and electrophoretic analysis revealed the presence of 1-5 plasmids. Six strains were plasmid-free. The magnitude of plasmids varied between 2 and 41.4 kb. The authors indicate possibilities of using the plasmid profile in the differentiation of strains.