Existence of a colonizing Staphylococcus aureus strain isolated in diabetic foot ulcers.

Staphylococcus aureus is an opportunistic bacterium capable of causing a wide range of severe diseases when it gains access to underlying tissues. Paradoxically, S. aureus is a common inhabitant of the skin microflora and colonizes the nares and other human mucosa. The purpose of this study was to determine genetic basis for the differences in pathogenic versus colonizing potential of S. aureus isolated from diabetic foot ulcers (DFU). By performing optical map comparisons of a collection of S. aureus strains isolated from DFU, we brought to light a prophage present in non-infecting bacteria. The phage, namely ROSA-like, was localized in a hotspot region ΦNM2 near the locus isd, the iron surface determinant system. The integrated phage reduces significantly the virulence of the strain and increases the biofilm formation. DFU seems to be a specific niche of this colonizing strain. The ROSA-like phage represents the first description of a mobile element present mainly in S. aureus isolated from DFU, which modulates the relationship of the bacteria with its human host. This phage appears to attenuate bacterial virulence and to promote colonization.