COMPARISON OF TRADITIONAL AND MOLECULAR METHODS OF TYPING ISOLATES OFSTAPHYLOCOCCUS-AUREUS

Fifty-nine Staphylococcus aureus isolates and 1 isolate of Staphylococ cus intermedius were typed by investigators at eight institutions by u sing either antibiograms, bacteriophage typing, biotyping, immunoblott ing, insertion sequence typing with IS257/431, multilocus enzyme elect rophoresis, restriction analysis of plasmid DNA, pulsed-field or field inversion gel electrophoresis, restriction analysis of PCR-amplified coagulase gene sequences, restriction fragment length polymorphism typ ing by using four staphylococcal genes as probes, or ribotyping. Isola tes from four well-characterized outbreaks (n = 29) and a collection o f organisms from two nursing homes were mixed with epidemiologically u nrelated stock strains from the Centers for Disease Control and Preven tion. Several isolates were included multiple times either within or b etween the sets of isolates to analyze the reproducibilities of the ty ping systems. Overall, the DNA-based techniques and immunoblotting wer e most effective in grouping outbreak-related strains, recognizing 27 to 29 of the 29 outbreak-related strains; however, they also tended to include 3 to 8 epidemiologically unrelated isolates in the slime stra in type. Restriction fragment length polymorphism methods with mec gen e-associated loci were less useful than other techniques for typing ox acillin-susceptible isolates. Phage typing, plasmid DNA restriction an alysis, and antibiogram analysis, the techniques most readily availabl e to clinical laboratories, identified 23 to 26 of 29 outbreak-related isolates and assigned 0 to 6 unrelated isolates to outbreak strain ty pes. No single technique was clearly superior to the others; however, biotyping, because it produced so many subtypes, did not effectively g roup outbreak-related strains of S. aureus.