Small-colony variants and phenotype switching of intracellular Staphylococcus aureus in chronic rhinosinusitis

Chronic rhinosinusitis (CRS) has been linked to the gram-positive bacteria Staphylococcus aureus (S. aureus) in its biofilm or intracellular forms. Recent evidence suggests that S. aureus also exists in a small-colony variant (SCV) form as a mechanism of altering its virulence capabilities. The aim of this study was to investigate the presence of SCVs in sinonasal mucosa of CRS patients and whether the phenomenon of phenotype switching can be applied to intracellular epithelial infections.

Sinonasal specimens were examined for the presence of intramucosal S. aureus and characterized to the strain level. An airway epithelial cell culture infection model was utilized to investigate whether bacteria were capable of alterations in virulence phenotype.

Intramucosal organisms harvested from sinonasal biopsies demonstrate phenotypic growth patterns and lack of coagulase activity consistent with SCVs. Intracellular infection of airway epithelial cell cultures with S. aureus led to decreased secretion of enterotoxins and phenotypic growth alterations consistent with SCVs.

Regulation of S. aureus virulence factors is a dynamic process, and exposure to the intracellular environment appears to provide the necessary conditions to enable these alterations in an attempt for the bacterium to survive and persist within host tissues. Further work is required to ascertain whether SCVs in CRS hold a clinically relevant pathogenic role in recalcitrant disease.