Use of contour-clamped homogeneous electric field (CHEF) electrophoresis to type methicillin-resistant Staphylococcus aureus.

Strains of methicillin-resistant Staphylococcus aureus (MRSA) from Australia and the UK were compared by digesting their chromosomal DNA with the low-frequency-cutting restriction enzyme SmaI and separating the restriction fragment length polymorphisms (RFLPs) by contour-clamped homogeneous electric field (CHEF) electrophoresis. The numbers of restriction fragments produced were in the range 14-17 and the sizes of the bands were 7-700 kb. Generally, the results confirmed previous conclusions based on antimicrobial resistance and plasmid profiles. The earlier MRSA isolates were different from more recent isolates, and the epidemic MRSA from eastern Australia (EA MRSA) was the same as the epidemic MRSA (EMRSA) found in London hospitals. However, contrary to previous results, the EA MRSA did not constitute a homogeneous group. The results showed that comparison of RFLPs by CHEF electrophoresis is a useful technique for studying the epidemiology of MRSA.