Objective: Comparative molecular analysis of S. aureus isolates of clonal complex 8 obtained from different epidemiological backgrounds (haMRSA, caMRSA, PVL+ MSSA).
Methods: Isolates were initially typed by spa-typing/BURP analysis, multilocus sequence typing (MLST)/eBURST analysis SmaI-macrorestriction analysis and SCCmec typing. Further strain characterization included susceptibility testing, as well as molecular detection of resistance and virulence genes. Representative isolates for each group were selected for subtractive suppressive hybridization (SSH) to identify putative group specific determinants.
Results: A total of 61 different DNA fragments belonging to 16 different genomic loci could be amplified selectively after subtractive hybridization. Twelve of these loci were confirmed as “group-specific” by subsequent PCR. Most of the DNA fragments were plasmid-located. Thus, the results reflected the clearly different plasmid content of the isolates investigated, which was confirmed by Southern Blot analysis of plasmid DNA. Beyond the plasmid-located determinants five chromosomal loci were shown to be group-specific, including the ACME cluster, SCCmec, SaPI5, parts of the serine-aspatat-repeat-protein cluster, as well as the membrane protein traG and associated DNA.
Conclusion: Comparative genomic analysis by SSH indicated that a considerable degree of variability within S. aureus clonal complex 8 might be due to differences in plasmid content and possession of alternative mobile genetic elements. Detailed characterization of group specific loci on plasmids as well as on the chromosome is essential before their suitability as genetic markers can be verified in a representative set of S. aureus isolates.