Phage set for methicillin-resistant Staphylococcus aureus (MRSA) strains combined with the international phage typing set and the phages from coagulase-negative staphylococci

（平成15年10月30日受付，平成16年6月11日受理） Phage typing has been a powerful tool for typing Staphylococcus aureus. However, when phage typing is applied to methicillin-resistant strains of S. aureus (MRSA), many strains remain nontypable (NT). In the previous report, most clinical isolates of methicillin-sensitive S. aureus (MSSA) could be grouped by a coagulase-negative staphylococci (CNS) phage set, as so-called type II. We tested 16 CNS phages for typing 158 strains of MRSA and the 22 phage propagating S. aureus strains. We chose four phages (Ph10, Ph12, U14, H96), because of their good discriminatory power, and added them to the international phage typing set (IPS) for S. aureus. These phages from CNS were classified as miscellaneous CNS group. The results obtained by this new combined phage set showed higher typeability and more discriminatory power than that by the IPS alone. Six MRSA isolates from an outbreak in a surgical ward were NT by the IPS. However, with these additional CNS phages, three isolates became typable as phage pattern Ph10/Ph12/U14 while others remained NT. These six strains were further analyzed according to their restriction fragment length polymorphism by pulsed-field gel electrophoresis (PFGE) using the restriction enzyme SmaI. PFGE patterns of these strains fell into two groups, which coincided with those by typing with the new combined phage set.