For phage typing, how many phages of staphylococcus aureus are used ?

Ans. is 'd' i.e., 23 Bacteriophage typing of staphylococcus is based on susceptibility of cocci to bacteriphages. This is carried out by pattern method where a set of 23 standard typing phages of S. aureus is used to type staphylococcal isolates and distinguish them from one another by their patterns of susceptibility to lysis. o The phage type of a strain is known by designation of the phages that lyse it. For example, if a strain is lysed by phages 83A, 84 and 85, it is called type 83A/84/85.