Description of a new group of variants of the Staphylococcus aureus elastin-binding protein that lacks an entire DNA segment of 180 bp

The elastin-binding protein (EbpS) is a microbial surface component recognizing adhesive matrix molecule (MSCRAM) found in Staphylococcus aureus that mediates bacterial cell binding to soluble elastin and tropoelastin. In scientific literature it is well established that the gene encoding for the elastin-binding protein (ebpS) is present in the vast majority of Staphylococcus aureus clinical isolates. The present study aimed at investigating a group of new variant forms of ebpS gene identified in S. aureus clinical strains isolated from implant-related orthopedic infections. A PCR screening for the ebpS gene, conducted on over two hundred S. aureus clinical isolates from implant-related infections revealed the detection of six strains exhibiting an altered amplicon size, shorter than expected. In order to elucidate the sequence changes present in these gene variants, the trait comprised between the primers was analyzed in all six isolates bearing the modification and in four isolates exhibiting the regular amplicon size. A similar form of the ebpS gene, lacking a DNA trait of 180 bp, was confirmed in all six isolates independently of their clonal origin. Interestingly, only three of these isolates, all with type IV polymorphism of the accessory genes regulator (agr) locus, showed exactly the same sequence and, thus, the same pattern of point mutations with respect to reference strains. From nucleotide translation, the corresponding encoded protein was found to lack an entire peptide segment of 60 amino acids. From nucleotide sequence translation, this modification was found to implicate the disappearance of an entire hydrophobic domain, whose functional significance needs to be further investigated.