The group A streptococcal collagen-like protein-1 (SCL1) is a key surface adhesin for biofilm formation.
Oliver-Kozup H; Martin K; Zhang L; Schwegler-Berry DE; Green BJ; Lukomski S
Abstract Book of the Eighteenth Lancefield International Symposium, September 4-8, 2011, Palermo, Italy. Milano, Italy: EAC, 2011 Sep; :88
GAS biofilm has been identified in human clinical specimens of the skin in the form of microcolonies encapsulated in an extracellular glycocalyx; however, the host and pathogen determinants mediating this process are not well defined. The Scl1 protein selectively binds to human extracellular matrix (ECM) component, cellular fibronectin (cFn). Objective: To test the hypothesis that Scl1-cFn binding promotes GAS biofilm formation. Methods and Results: Biofilm formation on plastic and cFn-coated surfaces by the wild-type M1 and M41 strains, and their isogenid sc/1-inactivated mutants, we compared spectrophotometrically following crystal violet staining. Both WT strains formed significantly richer biofilm on cFn than on plastic, indicating that cell anchoring with ECM strengthens the overall biofilm structure. Scl1 was essential for biofilm formation; complementation of Scl1 expression in the mutant restored biofilm to wild-type level. Human skin fibroblasts and lung epithelial cells deposit a cfn-rich natural ECm (nECM) with distinct supramolecular structure, and GAS cells preferentially recognize and attach to this structure, as evidenced by field emission scanning electron microscopy. Biofilm formed on nECM was comparable to that formed on commercial cFn and there was a statistically significant decrease in biofilm formed by both scl1 mutants as compared with the WT strains. Microcolony formation by the GFP-expressing GAS cells was also investigated in fibroblast-containing hydrogels using two-photon laser scanning fluorescence microscopy. We observed GAS chains closely associated with nECM deposited in 3-D space by the fibroblasts. Conclusions: Here, we (i) established that the Scl1 surface protein is an essential determinant of GAS biofilm, (ii) showed that the Scl1-cFn interaction provides an adherence mechanism facilitating biofilm stability, (iii) tested a physiologically relevant in vitro model of GAS biofilm, which utililzes 2-D nECM matirces deposited by human cells, and (iv) have developed a 8-D biofilm model using GAS and human cells embedded in tissue-like (hydrogel) milieu.
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