Comparison of heat shocking and acridine orange treatment in phage typing of nontypable strains of Staphylococcus aureus.

Forty-five percent of 108 nontypable strains of Staphylococcus aureus from clinical and environmental sources were phage typable after heat shock and acridine orange treatment. Although phage patterns were produced by different types of treatment, the same phage groups were present, showing specificity. The newly typable strains appear to be similar in phage group distribution to the primary typable strains typed at the Peter Bent Brigham Hospital during the same time period. Ten of the originally nontypable S. aureus strains that showed lytic patterns after heat shock or acridine orange treatment were subcultured four times from the treated culture and then tested again with bacteriophages. Phage patterns were still present in 8 of the 10 strains without any further treatment. These findings are compatible with the findings of other workers, who have shown that the insensitivity of primary nontypable S. aureus strains to phage is linked to phage-resistant genes in extrachromosomal genetic elements that can be "cured" by both heat shock and acridine treatment.