SALMONELLA-TYPHIMURIUM PLASMIDS SIMULTANEOUSLY CODING FOR TETRACYCLINE RESISTANCE, COLICIN PRODUCTION AND PATHOGENICITY

Two wild strains of S. typhimurium harboring two plasmids, of 90Kb and 100 Kb, were isolated from sewage water and clinical specimens. Exper iments of conjugation, curing and plasmid DNA analysis by agarose gel electrophoresis showed that the 100 Kb plasmid coded simultaneously fo r resistance to tetracycline (64 mu g/mL), production of colicin and p athogenicity to CFW mice. The 90 Kb plasmid, on the other hand, could be considered cryptic under the experimental conditions used in this s tudy. Curing with SDS affected only the heavier plasmid, when the bact erial strains lost the three characteristics at the same time. Conjuga tion experiments using E. coli and S. typhimurium showed that the tran sconjugants possessed either both or only the 100 Kb plasmid and that expression of tetracycline resistance and colicin production was assoc iated with the larger plasmid. To our knowledge, this is the first rep ort on the three properties studied being coded for simultaneously by the same plasmid in S. typhimurium.