Lambdoid Coliphages Conferring a Novel Pattern of Phage Sensitivity on Escherichia coli K12

Seven temperate coliphages recovered from naturally occurring lysogenic strains of Escherichia coli were found to lyse E. coli C but not K 12. Four of these C-specific phages produced mutants (hrk) able to grow on K cells. The K cells harbouring HK253hrk and HK183hrk were converted so that they could adsorb and be lysed by three other non-mutant C-specific phages. HK253, HK183 and two other phages were shown to recombine with phage lambda. Temperate coliphages HK250 and HK253 were recovered from lysogenic strains of Escherichia coli isolated from human faeces. They were found to form plaques on E. coli C but not on E. coli K12 and were designated as 'C-specific ' (Dhillon et al., 1980). Surveys of prophages present in naturally occurring strains of E. coli have shown coliphages of such restricted host range to be widespread (our unpublished observations). We have therefore undertaken a detailed study of HK250, HK253 and five other recent isolates of similar host range and the results are described below. The sources from which wild-type lysogenic E. coli strains were obtained are shown in Table 1. The composition of growth media such as tryptone broth (TB), tryptone yeast extract broth