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

Ans. is 'd' i.e., 23 o Bacteriophage typing of staphylococcus is based on susceptibility of cocci to bacteriphages.o 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.o For example, if a strain is lysed by phages 83A, 84 and 85, it is called type 83A/84/85.o Most of the strains of staphylococci can be classified by this method and are divided into five lytic groups.GroupPhageI29,52,52A, 79,80II3A,3C,55,71III6,42E, 47,53,54,75,77,83A, 84,85IV--V94,96Not allocated81.95