6(p-Hydroxyphenylazo)-uracil: a reversible, selective inhibitor of the replication of deoxyribonucleic acid of staphylococcal bacteriophage P11-M15.

6(p-Hydroxyphenylazo)-uracil (HPUra), a selective inhibitor of the semiconservative replication of deoxyribonucleic acid (DNA) of gram-positive bacteria, was found to inhibit the replication of DNA of bacteriophage P11-M15, a virulent derivative of the temperate Staphylococcus aureus bacteriophage P11. At appropriate concentration, HPUra inhibited DNA synthesis by P11-M15-infected S. aureus immediately and completely, regardless of the stage of the lytic cycle at which infected cells were exposed to drug. The effect of HPUra was reversible since the capacity of inhibited, infected cells to replicate phage DNA and produce mature phage could be restored by removal of HPUra from incubation media. Concentrations of HPUra which completely inhibited the replication of P11-M15 in its drug-sensitive host did not inhibit the replication of this phage or its DNA in several drug-resistant host mutants. HPUra also did not inhibit the replication of two other serologically distinct, virulent staphylococcal bacteriophages, P1 and 44AHJD, in drug-sensitive hosts.