In mixed cultures, a genetic factor (designated Hly factor) responsible for α-haemolysin production in 10 of 53 strains of was transmitted at a relatively high rate to other organisms, including shigellas and salmonellas as well as Transmission was evidently by conjugation for it was not achieved by bacteria-free culture fluids. Although the factor was not eliminated by acriflavine or ultraviolet irradiation, it was probably a plasmid. Salmonella recipients were very unstable, and during serial subculture in broth the Hly factor was lost from most of these organisms. The factor was easily reintroduced into these segregants, but with difficulty or not at all into the rare organisms which had lost it. Hly factor was transmitted independently of F, R and factors and phages were not involved in its transmission. Strains of K12 F+ into which Hly factor had been introduced became resistant to the F-specific phage. From this it appeared that the factor has the character observed in certain R factors. The illness produced in mice by the intravenous injection of culture fluids of α-haemolytic strains of was shown to be caused by the α-haemolysin itself.


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