Phage typing and phage induction in carrier and invasive Staphylococcus epidermidis isolates

Fifty-nine Staphylococcus epidermidis isolates (30 carrier and 29 invasive) were phage typed using the phage set developed by Pulverer. Poor results were obtained as only 24% of the invasive and 27% of the carrier isolates were typable, with no differences between these percentages (P greater than 0.05). Isolation of lysogenic phages present in the isolates was attempted by three different methods, induction being satisfactory only by overnight incubation with 0.1 mg l-1 mitomycin C and detection with 2,3,5-triphenyl-tetrazolium chloride. All isolates produced phages, and the lytic activity of these phages was expressed on more than 50% of the isolates in all cases (except one phage which lysed 10% of the carrier isolates and 13.8% of the invasive isolates). The percentages of isolates lysed in the two groups (carrier and invasive) were statistically different (P less than 0.05) only for phages derived from four isolates.