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Role of group A streptococcal virulence factors in adherence to keratinocytes
G L Darmstadt1, L Mentele, A Podbielski
1Departments of Pediatrics, University of Washington School of Medicine, Seattle, Washington 98105, USA.
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-protein-deficient (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-protein-deficient (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.
Insights
Group A Streptococcus skin infection initiation involves unique bacterial-keratinocyte interactions. Hyaluronic acid capsule impedes bacterial adhesin binding, suggesting its modulation is key in pathogenesis.
Area of Science:
- Microbiology
- Dermatology
- Infectious Diseases
Background:
- Group A Streptococcus (GAS) causes skin infections.
- Virulence factors like M protein and hyaluronic acid capsule are implicated in GAS pathogenesis.
- Understanding bacterial adherence to keratinocytes is crucial for elucidating skin infection mechanisms.
Purpose of the Study:
- To investigate the role of specific GAS virulence factors in the initiation of skin infections.
- To compare the adherence of wild-type GAS strains to isogenic mutants lacking key virulence genes.
- To identify bacterial and host factors mediating GAS adherence to human keratinocytes.
Main Methods:
- Generated 16 isogenic GAS mutants with inactivated virulence genes (e.g., emm, has, Opp).
- Assessed bacterial adherence to early-passage cultured human keratinocytes.
- Utilized enzymatic capsule digestion and soluble CD46 inhibition assays.
Main Results:
- Mutants lacking hyaluronic acid capsule (has) showed significantly increased adherence (13-fold).
- M-protein-deficient (emm) mutants did not exhibit reduced adherence; M protein is not essential for attachment.
- Oligopeptide permease (Opp) mutants displayed increased adherence with decreased capsule, while CD46 did not inhibit adherence.
Conclusions:
- Bacterial M protein and keratinocyte CD46 are not primary mediators of GAS adherence to keratinocytes.
- The hyaluronic acid capsule acts as a barrier, hindering bacterial adhesin-host receptor interactions.
- Modulation of capsule expression is likely important in GAS skin infection pathogenesis, with unique, unidentified molecular interactions involved in attachment.