Question

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

• A. 12
• B. 15
• C. 20
• D. 23

Hint:

Recall the standard international basic set size for Staph phage typing.

Answer 1

The Correct Option is D

Step 1: Bacteriophage typing of Staphylococcus aureus is an epidemiological tool based on the susceptibility of the cocci to a standard set of bacteriophages. It helps trace the source of infection in outbreaks.

Step 2: The technique uses the pattern method, in which a standard set of 23 typing phages is applied to the staphylococcal isolate. The strains are distinguished from one another by their individual patterns of susceptibility to lysis.

Step 3: The phage type of a strain is named by the phages that lyse it. For example, if a strain is lysed by phages 83A, 84 and 85, it is designated type 83A/84/85.

Step 4: Since the international basic set contains 23 typing phages, option (d) 23 is correct. The other figures (12, 15, 20) do not match the standard set size.