Role of group A streptococcal virulence factors in adherence to keratinocytes

To evaluate the role of putative group A streptococcal virulence factors in the initiation of skin infections, we compared the adherence of a wild-typ e M49-protein skin-associated strain to that of a series of 16 isogenic mut ants created by insertional inactivation of virulence genes. None of the mu tants, including the M-protein-deficient (emm mutant) strain, displayed red uced 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-, M 3-, 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 ina ctivation 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 M4 9-protein-deficient (emm mutant) and wild-type strains was increased to the same level (57 and 55%, respectively) following enzymatic digestion of the ir hyaluronic acid capsule, Adherence of mutants lacking oligopeptide perme ase (Opp) expression was increased 3.8- to 5.5-fold, in association with de creased cell-associated hyaluronic acid capsule. Finally, soluble CD46 fail ed 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 in teractions in attachment of skin strains of S, pyogenes to keratinocytes ar e unique and remain unidentified.