Natural population dynamics and expansion of pathogenic clones of Staphylococcus aureus

Abstract

The population structure of Staphylococcus aureus carried by healthy
\n humans was determined using a large strain collection of nonclinical
\n origin (n = 829). High-throughput amplified fragment length polymorphism
\n (AFLP) analysis revealed 3 major and 2 minor genetic clusters of S.
\n aureus, which were corroborated by multilocus sequence typing. Major AFLP
\n cluster I comprised 44.4% of the carriage isolates and showed additional
\n heterogeneity whereas major AFLP groups II and III presented 2 homogeneous
\n clusters, including 47.3% of all carriage isolates. Coanalysis of invasive
\n S. aureus strains and epidemic methicillin-resistant S. aureus (MRSA)
\n revealed that all major clusters contained invasive and multiresistant
\n isolates. However, clusters and subclusters with overrepresentation of
\n invasive isolates were also identified. Bacteremia in elderly adults, for
\n instance, was caused by a IVa cluster-derived strain significantly more
\n often than by strains from other AFLP clusters. Furthermore, expansion of
\n multiresistant clones or clones associated with skin disease (impetigo)
\n was detected, which suggests that epidemic potential is present in
\n pathogenic strains of S. aureus. In addition, the virulence gene encoding
\n Panton-Valentine leukocidin was significantly enriched in S. aureus
\n strains causing abscesses and arthritis in comparison with the carriage
\n group. We provide evidence that essentially any S. aureus genotype carried
\n by humans can transform into a life-threatening human pathogen but that
\n certain clones are more virulent than others.