Phages for methicillin-resistant Staphylococcus aureus: an international trial

An internationally agreed and validated set of phages is used worldwide for the typing of strains of Staphylococcus aureus of human origin. However, b ecause of the sometimes reduced susceptibility of methicillin-resistant str ains (MRSA) to these phages, some of the national typing centres use locall y isolated and characterized sets of experimental phages. In this trial, 42 such phages were distributed to 6 centres and tested against 744 isolates of MRSA with the intention of defining a phage set to augment the internati onal set. The use of these experimental phages increased the percentage typ ability from 75 % with the international set to 93% and the number of ident ifiable lytic patterns from 192 to 424. A subset of 10 experimental phages was selected. When this subset was compared with the experimental panel, th e typability rate was 91 % and 370 distinct patterns were obtained. This su bset of phages has been distributed for international trial.