An alternative method of phage-typingStaphylococcus aureus

Abstract

As many cultures ofStaph. aureusuntypable by the international basic-set phages at RTD were typed by a block of 20 extra phages at RTD as by the basic set at RTD × 1000. Reproducibility of the lytic patterns was as good with the extra phages at RTD as with the basic-set phages at RTD, and better than with the basic-set phages at RTD × 1000.A method of assessing redundancy in any set of phages is presented, and a ‘3-strong differences’ rule is suggested for discriminating between cultures of staphylococci from patterns of phage lysis by the combined set of phages at RTD.Experience with the combined set of phages suggests that it may be possible to improve the phage-typing of staphylococci by substituting a larger series of phages used only at RTD, for the present set of 22 phages used at RTD and RTD × 1000.