Typing of Staphylococcus aureus colonising human nasal carriers by pulsed-field gel electrophoresis.

Colonisation by Staphylococcus aureus in the nares of 120 outpatients and 63 healthy adults was studied for c. 2 years. Two states of carriage of S. aureus were confirmed: persistent carriage and persistent non-carriage. The states of carriage and non-carriage were quite stable and > 60% of the population of any of the study groups were stable non-carriers. The results of typing the strains isolated from the same individuals at different times with DNA fingerprinting by digestion with SmaI enzyme showed that all the stable carriers were persistently infected with the same strain and that changes in the strain seldom occurred.