Typing of Staphylococcus aureus isolated from nasal carriers.

Eighteen Staphylococcus aureus strains (9 pairs) were isolated from 9 apparently healthy persons (including 5 persons from medical staff) regarded as persistent nasal carriers in a 5-7-day or 3-5-month period, respectively. The 18 S. aureus strains were characterized phenotypically and by genotypic methods. Biochemical properties determined with a commercial identification system, production of haemolysins as well as most of the antibiotic resistance date revealed an identity between both strains of each pair. This putative identity was confirmed for most of the paired strains by phage typing and plasmid profiling for all 9 pairs by determination of the number of repeats in the X region of the spa gene and by macrorestriction analysis of the chromosomal DNA of the isolates. The present results indicate that a single clone of S. aureus might colonize continuously persistent nasal carriers over a 5-7 day period, even for a period of 3-5 months.