Comparative studies on generalized transducing bacteriophages of Proteus mirabilis, phim and pi1.

Comparative studies were made on the generalized transducing bacteriophages of Proteus mirabilis phim (Nakaya and Rownd), pi1(Böhme), and a clear plaque-forming mutant phim-c, derived from phim. Electron microscopic observations revealed that these phages were morphologically identical, indicating that they belonged to the group C of Bradley's classification, or to the type C1 of Ackermann's classification. Phages phim and pi1 formed characteristic turbid plaques different from each other, and the plaques of pi1 were smaller in size than those of phim. The plaques of phage phim-c were clear and also were the largest in size among those studied. Average latent periods of phim and pi1 were 70 and 60 min, respectively. Average burst size was found to be 30 and 10 plaque-forming units per infected cell for phim and pi1, respectively. It was confirmed by cross neutralization tests that phim and pi1 differed serologically from each other. The host range of the two phages also differed, and phage phim was more sensitive to heat than pi1. These results indicate that phages phim and pi1 are different types of phages. Majority of the properties of phage phim-c were nearly identical with those of phage phim except that the multiplication of phim-c was more strongly inhibited by methylene blue than that of phim and pi1. Phage phim-c is considered to be a clear mutant of phim.