Comparison of protein A gene sequencing with pulsed-field cel electrophoresis and epidemiologic data for molecular typing of methicillin-resistant Staphylococcus aureus

The epidemiologic relatedness of methicillin-resistant Staphylococcus aureu s (MRSA) isolates is currently determined by analysis of chromosomal DNA re striction patterns by pulsed-field gel electrophoresis (PFGE). We have eval uated an alternative typing system (MicroSeq StaphTrack Kit; Perkin-Elmer B iosystems) based on the sequence analysis of the chromosomally encoded poly morphic repeat X region of the S. aureus protein A (spa) gene. A total of 6 9 clinical MRSA isolates were divided into 18 groups according to the numbe r and nucleotide sequences of the spa repeats. Molecular typing results obt ained both by spa sequencing and from the PFGE patterns were concordant exc ept for one group, which contained 20 isolates recovered over a 2-year peri od from hospitalized patients at the Mayo Clinic. Although the spa typing p atterns were indistinguishable for those isolates? PFGE analysis yielded se ven related but distinguishable patterns. Further coagulase gene sequence a nalysis subtyped those 20 strains into four groups which followed distinct temporal and geographic distributions. During a 2-year epidemic period ther e were up to 7 fragment changes in PFGE patterns among epidemiologically re lated isolates, suggesting that PFGE may be unsuitable for long-term typing of strains involved in epidemics. Although more limited than PFGE in discr iminatory power, spa sequencing analysis could be used as a screening metho d for typing of MRSA strains because of the shorter turnaround time, ease o f use, and the inherent advantages of sequence analysis, storage, and shari ng of information.