Restriction enzyme analysis of plasmid DNA and bacteriophage typing of paired Staphylococcus aureus blood culture isolates.

We compared restriction enzyme analysis of plasmid (REAP) DNA profiling with bacteriophage typing for determination of similarities and differences among 50 pairs of Staphylococcus aureus blood isolates from patients with multiple positive blood cultures. Isolates from 17 pairs did not have detectable plasmids. Isolates from 33 pairs had plasmids classified into 17 distinct REAP DNA profiles. Paired isolates from 31 of these episodes were identical to one another. By phage typing, 35 pairs had strong lytic reactions to a phage(s), 9 pairs lacked strong reactions, and 6 pairs consisted of a strongly reactive isolate and an isolate with no strong reaction to a phage. When consolidated into 11 general phage groups, pairs from 44 of the 50 episodes were in the same general group. REAP DNA profiles were highly reproducible (99%), whereas phage typing was not. REAP DNA profiling is superior to phage typing as a technique for determining similarities and differences among S. aureus blood isolates.