EVOLUTION OF AN ENDEMIC METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS POPULATION IN AN AUSTRALIAN HOSPITAL FROM 1967 TO 1996

The evolution over 30 years of a population of methicillin-resistant S taphylococcus aureus (MRSA) from a tertiary referral hospital was stud ied by phylogenetic analysis of SmaI-generated restriction fragment le ngth polymorphisms (RFLPs), The results suggest that a new clone of MR SA appeared at the hospital in the early 1980s, which, although usuall y retaining its ancestral phage-type, developed four different RFLP pu lsotypes in the next 16 years, This finding indicates that multiple RF LP patterns in MRSA do not necessarily represent multiple clones deriv ing from different mec gene transfer events, Such variation within a c lone may be significant in the interpretation of RFLP patterns during outbreaks and emphasizes the need to use two typing methods in studies of such populations, Since the appearance of new clones of MRSA is a relatively rare event, cross-infection control is paramount in the pre vention of MRSA dissemination.