28 mutant showed ~44% reduction in 24 h biofilm. We propose that several surface proteins Belinostat contribute to biofilm formation by M28-type strains including proteins AspA and Scl1.28, and potentially, proteins F1/SfbI and F2 that are also present in these strains [22]. This redundancy is likely responsible for the observed residual biofilms produced by the AspA- and Scl1.28-deficient

mutants. The observed heterogeneity in biofilm architecture of different GAS strains was previously observed by Lembke et al. [28] and was also documented in the current study using FESEM. In addition, here we report the differences in GAS-cell surface morphology and within cell-to-cell junctions in biofilms formed by M1- and M41-type strains. The structural and genetic determination of these differences is not known since M41 genome has not been sequenced, but may be associated with the presence of additional surface proteins, such as the F2 protein [55] encoded by prtf2 gene found in this strain [22]. Even more striking was an observed difference in the Epigenetics Compound Library supplier amount of the extracellular material associated with each strain, referred to as BAEM (bacteria-associated extracellular matrix). It has been shown that extracellular matrix, also called glycocalyx,

is produced by biofilm-forming bacteria. DNA, lipids, proteins [33], polysaccharides and dead cell debris [56] were identified in this matrix and for gram-positive bacteria, teichoic acids have also been detected [57, 58]. The exopolysaccharide

component of the glycocalyx is detected using carbohydrate-binding Resminostat lectins, such as concanavalin A (ConA) [10]. Both FESEM analysis and ConA staining detected more BAEM associated with M1 biofilm compared to M41, which produced larger biofilm. These observations suggest that GAS biofilm is stabilized differently by different strains and that higher BAEM production does not necessarily pre-determine larger biofilm mass. Consequently, a combination of biofilm features rather than biofilm size alone may be more relevant to pathogenicity of a given GAS strain. Diminished adherence and biofilm formation could be associated with changes in cell surface hydrophobicity [59] of the scl1 mutants. Indeed, the lack of Scl1 resulted in both decreased hydrophobicity and the ability to form biofilm, albeit in a somewhat disproportionate manner. A decrease in the hydrophobicity index by only ~8%, as compared to the wild type-strain, was measured for the M41Δscl1 mutant and this modest decrease was accompanied by a rather large reduction in biofilm formation capacity after 24 h by 30%. Greater decrease in cell-surface hydrophobicity was measured for the M1Δscl1 (~21%) and M28Δscl1 (~22%) mutants, which was accompanied by a significant loss in biofilm formation after 24 h by both isogenic strains by ~55% and ~41% (P ≤ 0.001 for each comparison), respectively. In addition, heterologous expression of Scl.41 in L.