Genetic variability in the sdrD gene in Staphylococcus aureus from healthy nasal carriers

Abstract

<p><i>Background</i>: <i>Staphylococcus aureus</i> cell wall anchored Serine Aspartate repeat containing protein D (<i>sdrD</i>) is a member of the microbial surface component recognising adhesive matrix molecules (MSCRAMMs). It is involved in the bacterial adhesion and virulence. However the extent of genetic variation in <i>S. aureus sdrD</i> gene within isolates from healthy carriers are not known. The aim of this study was to evaluate allelic variation of the <i>sdrD</i>gene among <i>S. aureus</i> from healthy nasal carriers.</p>

<p><i>Results</i>: The <i>sdrD</i> A region from 48 <i>S. aureus</i> isolates from healthy carriers were analysed and classified into seven variants. Variations in the <i>sdrD</i> A region were concentrated in the N2 and N3 subdomains. Sequence analysis of the entire <i>sdrD</i> gene of representative isolates revealed variations in the SD repeat and the EF motifs of the B repeat. In silico structural modelling indicates that there are no differences in the <i>sdrD</i> structure of the 7 variants. Variable amino acid residues mapped onto the 3D structure revealed that the variations are surface located, exist within the groove between the N2-N3 subdomains and distributed mainly on the N3 subdomain. Comparison of adhesion to keratinocytes in an in vitro cell adhesion assay, using NCTC 8325–4∆<i>sdrD</i> strains expressing the various <i>sdrD</i> gene variants, indicated a significant difference between only two complements while others showed no major difference in their adhesion.</p>

<p><i>Conclusions</i>: This study provides evidence of sequence variations across the different domains of <i>sdrD</i> from <i>S. aureus</i> isolated from healthy nasal carriers. Proper understanding of these variations is necessary in the study of <i>S. aureus</i> pathogenesis.