Evaluation of intraspecies interference due to agr polymorphism in Staphylococcus aureus during infection and colonization.

In Staphylococcus aureus infection, intraspecies cross-inhibition mediated by the regulatory system agr may lead to the exclusion of heterologous strains at the site of infection or colonization. We analyzed consecutive and cocolonizing strains (classified as different clones by pulsed-field gel electrophoresis) from patients with cystic fibrosis (CF) and healthy individuals. Strain replacement was accompanied by a change in the agr group in 80% of the patients with CF and in 63% of the healthy individuals. Cocolonizing strains from patients with CF were shown to belong to interfering agr groups in 6 of 10 cases. In contrast, in healthy individuals, cocolonization of the nares with strains of interfering agr groups was rarely observed. agr polymorphism has no impact on the colonization dynamics of S. aureus in patients with CF but may influence nasal colonization in health individuals.