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Summary. Death rates have been determined for staphylococcal strains dried on cotton blanket material and stored at room temperature in the dark and in the light. Methicillin-resistant Staphylococcus aureus (MRSA) strains that produced a golden pigment and had a wide distribution within the hospital survived for longer periods than MRSA strains that produced little pigment and had a restricted local distribution. Death rates of methicillin-sensitive strains of S. aureus at day 7 were similar to those of the general epidemic MRSA strains, and there was no significant difference between the death rates at day 7 of the local epidemic MRSA strains and the coagulase-negative strains.

The genomic DNA of 58 isolates of methicillin-resistant Staphylococcus aureus (MRSA) obtained during an infection outbreak at two major Canberra hospitals was analysed for restriction fragment length polymorphism (RFLP) by digestion with the endonuclease SmaI and resolution of the fragments by pulsed-field gel electrophoresis. Based on the fraction of common fragments generated by the endonuclease, DNA similarities among the isolates were estimated. Distance matrix analysis showed that the MRSA isolates could be divided into two major clusters (RFLP types I and 11) and one minor one (type 46). A fourth group of miscellaneous isolates was found to be heterogeneous in terms of DNA sequence similarity. The epidemiological data indicated that RFLP type I was most common in the intensive care units in the two hospitals, with particular subtypes of RFLP type I concentrated in individual units. RFLP type I1 and the miscellaneous group were more generally distributed. Type 46 isolates appear to be related to a group which was present in epidemics in Melbourne hospitals in the early 1980s. Using the standard phage set, the RFLP type I group was largely untypable. However, type I1 isolates were all phage typable, with a shared susceptibility to phages 29/85/95/90; type 46 isolates had a shared susceptibility to phages 85/90. The miscellaneous isolates were of variable phage types.

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Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) susceptible to gentamicin has been reported in a number of countries in the 1990s. To study the acquisition of gentamicin-sensitive MRSA (GS-MRSA) in southeast Queensland and the relatedness of GS-MRSA to other strains of MRSA, 35 cases of infection due to GS-MRSA from October 1997 through September 1998 were examined retrospectively to determine the mode of acquisition and risk factors for MRSA acquisition. Thirty-one isolates from the cases were examined using a variety of methods (antibiotyping, phage typing, pulsed-field gel electrophoresis [PFGE] fingerprinting, and coagulase typing by restriction analysis of PCR products) and were compared with strains of local hospital-acquired gentamicin-resistant MRSA (GR-MRSA) and of Western Australian MRSA (WA-MRSA). Only 6 of 23 cases of community-acquired GS-MRSA had risk factors for MRSA acquisition. Twenty of 21 isolates from cases of community-acquired infection were found to be related by PFGE and coagulase typing and had similar phage typing patterns. Hospital-and nursing home-acquired GS-MRSA strains were genetically and phenotypically diverse. Community-acquired GS-MRSA strains were not related to nosocomial GR-MRSA or WA-MRSA, but phage typing results suggest that they are related to GS-MRSA previously reported in New Zealand.