Phages l and I2-2: IncI Plasmid-dependent Bacteriophages

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Abstract
Phage 1.alpha. was isolated from sewage from Windhoek, South West Africa. It formed relatively clear plaques about 2 mm in diameter, on sensitive strains of Escherichia coli K12 and Salmonella typhimurium LT2. The phage had a hexagonal outline with a diameter of about 24 nm, contained RNA and was resistant to chloroform. Phase 1.alpha. formed plaques or propagated only on organisms carrying I1 plasmids or the I.gamma. plasmids R621a. The efficiency of plating was higher on E. coli than on S. typhimurium hosts. The phage adsorbed along the length of shafts of I1 pili. Phage I2-2 was isolated from Pretoria [South Africa], sewage. It was filamentous virus and individual virions varied considerably in length. Phage I2-2 formed turbid plaques which varied from pin point to about 1 mm in diameter on all hosts. It was resistant to RNase and sensitive to chloroform. Phage I2-2 had a spectrum of activity limited to strains harboring I2 plasmids but the adsorption site could not be demonstrated. The phase was not related serologically to phages If1 or PR64FS.