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Abstract
Cultures of Escherichia coli carrying Coll plasmids received in conjugation from strains of Salmonella typhimurium and S. agona were examined for abortive infection (Abi) of phage BF23 and for enhanced resistance to the lethal action of UV-irradiation (Uvr). The Abi character of stored cultures of E. coli was also compared with the reaction of the same stock culture tested 5 years before. Seven of the eight potential types differentiated by three characters were represented among 160 Coll plasmids: Colla Abi+ Uvr+ (3 plasmids), Colla Abi– Uvr+ (1), Colla Abi– Uvr– (2), Collb Abi+ Uvr+ (85), Collb Abi+ Uvr– (5), Collb Abi– Uvr+ (4), Collb Abi– Uvr– (60). Recognition that different plasmid types could be carried by strains of a clone proved useful in the interpretation of the epidemic spread of strains of S. typhimurium of phage type/biotype 141/9f in Scotland and in tracing the ancestry of a recently emerged rhamnose non-fermenting mutant strain of S. agona.
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