pJT2: Unusual H1 Plasmid in a Highly Virulent Lactose-Positive and Chloramphenicol-Resistant Salmonella typhimurium Strain from Calves

A lactose-positive and chloramphenicol-resistant strain of Salmonella typhimurium of high virulence was isolated from an outbreak of enteric and septicemic salmonellosis in veal calves. The lactose-positive marker was located on an Hi plasmid, pJT2, together with resistance to chloramphenicol, streptomycin, sulfonamides, and tetracycline. pJT2 was unusually large and had a molecular weight ofabout 150 x 106. A similar plasmid was also present in a third of the Escherichia coli strains isolated from the intestines of septicemic calves during the outbreak. Spontaneously derived Lac- derivatives of pJT2 had an approximate molecular weight of 140 x 106.

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