Molecular relatedness of Staphylococcus aureus typing phages measured by DNA hybridization and by high resolution thermal denaturation analysis.

Fifteen bacteriophages representative of the serological and lytic groups of the International Typing Set for Staphylococcus aureus were examined for genomic homology by DNA hybridization and by analysis of high resolution thermal denaturation profiles. Phages 11 and 80 alpha, not part of the set, were also examined. DNA homology measured by filter hybridization showed values ranging from near zero to 88 per cent in pair-wise comparisons. Cluster analysis of these data by standard numerical taxonomical methods yielded clusters which closely reflect the subdivision of the international set on the basis of serological reactions. High resolution thermal denaturation analysis yielded characteristic profiles for each phage DNA, with members closely related by hybridization analysis showing only minor differences. Quantitative analysis of the extent of overlap of these profiles generated relational values which were subjected to the same numerical taxonomic analysis as for the DNA hybridization data. The resultant dendrogram was qualitatively different only in minor respects from that derived from the hybridization analyses, but quantitatively homology was greater by 80 per cent or more for the DNAs which were least related according to the hybridization analyses. This upward shift in measured homology appears to reflect the similar base composition of the DNAs from these phages. Statistical comparison of the homology data obtained by the two methods showed them to be significantly correlated. These results indicate that the International Typing Set consists of phages which all appear to be related to a greater or lesser extent. If, as the history of the collection of these phages indicates, they are a random sample of aureophages, then this group of phages may represent a common genetic pool within which recombination, mutation, and genome rearrangement occur to generate unique individual phages.