Role of Group A Streptococcal Virulence Factors in Adherence to Keratinocytes

Abstract

To evaluate the role of putative group A streptococcal virulence factors in the initiation of skin infections, we compared the adherence of a wild-type M49-protein skin-associated strain to that of a series of 16 isogenic mutants created by insertional inactivation of virulence genes. None of the mutants, including the M-proteindeficient (emm mutant) strain, displayed reduced adherence to early-passage cultured human keratinocytes, but adherence of the mutant lacking hyaluronic acid capsule expression (has mutant) was increased 13-fold. In contrast, elimination of capsule expression in M2-, M3-, and M18-protein has mutants increased adherence only slightly (1.3-to 2.3-fold) compared to their respective wild-type strains. A mutant with inactivation of both emm and has displayed high-level adherence (34.9 ؎ 4.1%) equal to that of the has mutant strain (40.7 ؉ 8.0%), confirming the lack of involvement of M49 protein in attachment. Moreover, adherence of the M49-proteindeficient (emm mutant) and wild-type strains was increased to the same level (57 and 55%, respectively) following enzymatic digestion of their hyaluronic acid capsule. Adherence of mutants lacking oligopeptide permease (Opp) expression was increased 3.8-to 5.5-fold, in association with decreased cell-associated hyaluronic acid capsule. Finally, soluble CD46 failed to inhibit adherence of M49-and M52-serotype skin strains. We conclude that (i) bacterial M protein and keratinocyte CD46 do not mediate adherence of M49 skin-associated Streptococcus pyogenes to epidermal keratinocytes, (ii) hyaluronic acid capsule impedes the interaction of bacterial adhesins with keratinocyte receptors, (iii) modulation of capsule expression may be important in the pathogenesis of skin infections, and (iv) the molecular interactions in attachment of skin strains of S. pyogenes to keratinocytes are unique and remain unidentified.Streptococcus pyogenes (group A streptococcus) is unsurpassed among bacterial pathogens in its ability to cause a variety of skin infections ranging from self-limited superficial impetigo to fulminant life-threatening, soft-tissue destruction and necrotizing fasciitis (26-28). Increased global incidence of severe, invasive disease due to S. pyogenes over the past decade, with the skin serving as the portal of entry in more than half of the cases, has highlighted our need to understand the molecular pathogenesis of skin infections (66). Pathogenic mechanisms of streptococcal skin infections are almost entirely unknown, however, since efforts have focused on the interaction of streptococci with mucosal epithelium, and in vitro models which emulate human skin disease (23) have not been available.An initial step in group A streptococcal skin infection appears to involve adherence of the bacteria via its adhesin(s) to host cell receptor(s) (25). The type of adhesin utilized for specific binding may vary depending on the streptococcal strain and type of host cell and tissue involved. M protein is the most well-documented virulence factor of S. pyogenes. ...

Streptococcus pyogenes Collagen Type I-binding Cpa Surface Protein

“…Most interestingly, there was no consistent evidence for enhanced cpa expression in the presence of collagen type I peptide fragments as seen in other streptococcal species (44,83,84). However, the presence of collagen peptides did influence expression of two S. pyogenes regulatory genes, mga and nra.…”

Group A streptococcal RofA-type global regulators exhibit a strain-specific genomic presence and regulation pattern

“…However, the decreased expression of genes involved in capsule synthesis in the mutant could contribute to the observed effects. Inactivation of the has operon in the M2 strain increased its adherence to keratinocytes by a factor of two (Darmstadt et al, 2000).…”

CsrRS Regulates Group BStreptococcusVirulence Gene Expression in Response to Environmental pH: a New Perspective on Vaccine Development

“…Peptide uptake may be important not only for nutritional requirements under acid stress but also for bacterial attachment to the vaginal epithelium. For example, in S. pneumoniae and GAS, the oligopeptide permease modulates the adherence of the bacteria to human host cells (13,14), while in GBS it stimulates adherence to human epithelial cells and modulates their binding to fibrinogen and fibronectin (49). The fact that responses of GBS to variations in pH in large part required the CsrRS system led us to hypothesize that during GBS pathogenesis, CsrRS mediates the adaptation of the organism to the acidic environment of the vagina and to more-basic compartments, such as the amniotic fluid and neonatal lung.…”