Characterisation of methicillin-resistant Staphylococcus aureus isolates by restriction endonuclease digestion of chromosomal DNA.

Clinical isolates of Staphylococcus aureus from the London Hospital were characterised by genetic analysis of antibiotic-resistance determinants and by restriction endonuclease digestion of chromosomal DNA and compared with isolates from elsewhere in the UK. Restriction enzyme digestion of chromosomal DNA confirmed that a single strain of methicillin-resistant S. aureus (MRSA) persists at the London Hospital, although its antibiotic-resistance profile and plasmid carriage are not constant. Methicillin-sensitive isolates, on the other hand, each had readily distinguishable and unique DNA restriction patterns. The DNA restriction digest pattern of the London Hospital MRSA isolates was identical to that of "epidemic" (E) MRSA isolates from the Thames regions. By contrast, other MRSA isolates had DNA restriction patterns which differed from those of EMRSA isolates and from each other. These results confirm the discriminatory value of restriction pattern analysis as a typing method.