Genome organisation of Staphylococcus aureus isolates from different populations

Isolates from three different Staphylococcus aureus populations were examined for restriction fragment length polymorphisms (RFLPs) of total DNA digested with the endonuclease SmaI. The populations were: community S. aureus isolates collected at random from healthy individuals (38 isolates); methicillin-resistant S. aureus (MRSA) type strains involved in separate outbreaks of infection in Melbourne (1982) and Canberra (1990) (two isolates); and a collection of clinical methicillin-sensitive S. aureus (MSSA) causing hospital infection (20 isolates). RFLPs with CspI and SmaI and hybridisation analyses of both, showed that the community and the MSSA isolates were not genetically closely related, and, accordingly, they could not be grouped into clusters as seen with the MRSA types. However, a few MSSA isolates were found to be closely related to each other and appeared to be similar to the standard strain S. aureus 8325-4 and to some MRSA types. Although there was substantial variability between the three groups, physical mapping with genomic DNA fragments from the standard strain S. aureus 8325-4 to probe large fragments generated with CspI and SmaI from the chromosomes of selected community and MRSA isolates, demonstrated a well conserved genome organisation between representative isolates from the three groups.