Objective: Analysis of the genomic background of methicillin-resistant Staphylococcus aureus isolates from skin and soft tissue infections (SSTI) revealing conflicting results by use of spa-typing and alternative typing techniques.
Methods: Typing was conducted by use of spa-typing/BURP analysis, multilocus sequence typing (MLST)/eBURST analysis and SmaI-macrorestriction analysis. Further strain characterization included susceptibility testing, as well as molecular detection of resistance and virulence genes. Representative isolates were characterized by sequencing of the sas genes and additional PCR and DNA sequencing of relevant genome regions.
Results: Based on typing results of the German reference centre for staphylococci we found a highly resistant “new” MRSA clone associated with infection of the skin and wound infections, respectively. This clone was tentatively allocated to clonal complex 8 (CC8) based on spa-typing/BURP analysis, but revealed belonging to CC45 by use of alternative typing techniques. Molecular characterization of corresponding isolates demonstrated a large chromosomal replacement involving progenitors of CC8 and CC45.
Conclusion: Our results demonstrate one limitation of the single locus dependent spa-typing method. As demonstrated previously, large chromosomal replacements encompassing the spa-locus might lead to incorrect group assignment of isolates by BURP grouping. However, this phenomenon was demonstrated so far only for particular clonal groups. Our results indicate that recombination events affect a wider range of clonal lineages than assumed so far.