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Lysogenic conversion of Staphylococcus aureus to loss of β-hemolysin production by serological group F phages is always associated with gain in staphylokinase production. In this study, the new phages belonging to serotype F were detected during the course of isolation of phages from Staph aureus of bovine origin and some characteristics of the new phages isolated were investigated. The new phages, φ47O and φ499, isolated from Staph aureus producing β-hemolysin and staphylokinase(β^+ K^+) were found to convert β^+K^+ strain to β^+K^+, Staph aureus strains lysogenized by this serotype F single-converting phage φ470 or φ499 could be again lysogenized with serotype F double-converting phage φ506. The frequency of lysogenization of indicator strains by serotype F single-converting phage was 100%. whereas the frequency for serotype F double-converting phage φ506 varied from 4.2% to 97.6% according to the indicator strains. The indicator strain lysogenized with phage φ470 was resistant to phage φ499, and vice versa, but not to phage φ506. Therefore, phage φ470 and φ499 were shown to be identical by immunity test.
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