Carriage rate of phages in different groups and biotypes of P. acnes. Phages were induced with 2 μg/ml mitomycin C, lysate sterile filtered and stored for seven days to screen out unstable phages. The lysate was then applied at different concentrations to an overlay plate with the host isolate. If plaques were observed after two days, the sample was regarded positive for phages. (A) A comparison in carriage rate of inducible phages between deep isolates (AD), skin isolates (AS) and biotype IA, IB and II. (B) A comparison of carriage rate of inducible phages in biotype IB between deep isolates and isolates from skin induced by 2 μg/ml mitomycin C.