Ecological Temporal Stability of Staphylococcus aureus Nasal Carriage

We described the colonization dynamics of Staphylococcus aureus in a group of 266 healthy carriers over a period of approximately 1 year. We used precise genotyping methods, i.e., amplified fragment length polymor-phism (AFLP), spa typing, and double-locus sequence typing (DLST), to detect changes in strain identity. Strain change took place rather rarely: out of 89 carriers who had initially been colonized, only 7 acquired a strain different from the original one. Approximately one-third of the carriers eliminated the colonization, and a similar number became newly colonized. Some of these events probably represent detection failure rather than genuine colonization loss or acquisition. Lower bacterial counts were associated with increased proba-bility of eliminating the colonization. We have confirmed a high mutation rate in the spa locus: 6 out of 53 strains underwent mutation in the spa locus. There was no overall change in S. aureus genotype composition. Staphylococcus aureus is an important human pathogen responsible for both nosocomial and community-acquired infections, but it also asymptomatically colonizes a large fraction of humans (20 to 60%). Although most carriers never experience health problems related to colonization, it is estimated that 80 % of infections with S. aureus are en