Molecular studies of an fi+ plasmid from strains of Salmonella typhimurium |
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Authors: | H R Smith G O Humphreys N D F Grindley June N Grindley and E S Anderson |
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Institution: | (1) Enteric Reference Laboratory, Public Health Laboratory Service, London |
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Abstract: | Summary Plasmid DNA has been isolated from five fi
+ strains of Salmonella typhimurium of independent origin, including type 36 and LT2. The mean contour length of the plasmids was between 27.3 and 29.3 m. A variant line of S. typhimurium type 36 which was fi
- yeilded no plasmid DNA. These results support the hypothesis that the fi
+ property of S. typhimurium is coded by a plasmid. In S. typhimurium 36 this plasmid, designated MP1036, also appears to code for restriction of non-donor-specific phages. Molecular studies indicate that superinfection of S. typhimurium 36 with the kanamycin resistance determinant K, which results in loss of the fi
+ property, is correlated with loss of MP1036. Reassociation experiments demonstrate a high degree of homology between the DNA of all five S. typhimurium plasmids, and between MP1036 and K. MP1036 has some homology with F and F-like R factors, but not with plasmids of other compatibility groups. A recombinant between an ampicillin resistance determinant and MP1036 is autotransferable at low frequency. The significance of these findings is discussed. |
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