Sodium dodecyl sulphate polyacrylamide gel electrophoresis of sulphur-35 methionine labelled cellular proteins of Staphylococcus aureus resistant to methicillin was used as a typing method during an outbreak on a cardiothoracic ward. This showed that the outbreak strain was indistinguishable from the epidemic strain of methicillin resistant S aureus prevalent in London. In contrast, 44 epidemiologically separate strains of S aureus gave individually distinct radiolabelled protein profiles. This

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... method permitted rapid confirmation that an epidemic strain was responsible and indicated the need for urgent control measures.