The role of lysogeny in the modification of phage typing patterns of Staphylococcus aureus isolated from dairy cows

Strains of Staphylococcus aureus were isolated at a single sampling from cows in a dairy herd. When typed by phage most showed a complex pattern of lysis with group III and IV phages. Cross-spotting of strains showed great lytic activity and ten phages were isolated. The parent strains were lysogenized with these phages and the effect on the phage typing pattern of 202 daughter strains from 25 parent cultures was studied. Phage action was often blocked completely, with up to four being blocked on the one strain. Those most frequently blocked were phage 101, 117, 367 and 42D.