Bacterial biomass was evaluated spectrophotometrically following crystal violet staining at 1, 6, 12, and 24 h time points, representing different stages of biofilm formation, and absorbance values rendered for the WT and Δscl1 isogenic mutant strains were compared. The M41Δscl1 mutant showed a 29-35% decrease in biofilm formation (the OD600 value obtained for the WT strain at each time point was considered 100%), which was Fulvestrant sustained throughout all time points. This reduction was statistically significant at initial adherence (1 h), as well as during biofilm development

(6-12 h) and at maturation (24 h) (Figure 2a; P ≤ 0.05 at 1 and 12 h, P ≤ 0.001 at 6 and 24 h). Complementation of Scl1.41 expression in the M41Δscl1 mutant (M41 C) restored its ability to form biofilm to WT levels. Similarly, the M28Δscl1 mutant had a significantly decreased capacity for biofilm formation in the range of 29-44%

as compared to WT strain (Figure 2b; P ≤ 0.05 at 1 and 6 h, P ≤ 0.001 at 3, 12 and 24 h). Likewise, there was a statistically significant decrease in M1Δscl1 biofilm biomass by ~42-75% compared to the WT strain (Figure 2c; P ≤ 0.001 at 1-24 h). CLSM analysis of corresponding 24-h biofilms of these strains confirmed our crystal violet staining results at 24 h. The Δscl1 mutants had substantially decreased average biofilm thickness by more than 50% (mean values) as compared to the selleckchem parental WT organisms check details (Figure 2d-f). While these low average biofilm thickness values measured for the M1Δscl41 (6 μM) and M28Δscl1 (5 μM) correspond to residual biofilms made by those mutants (Additional file 1: Figure S1a-d), by comparison, the M1Δscl1 (4

μM) was shown not to produce a continuous biofilm layer under these conditions (Additional file 1: Figure S1e-f). Our data support the hypothesis that the Scl1 protein plays an important functional role during GAS biofilm formation and that Scl1 contribution varies among GAS strains with different genetic backgrounds. Scl1 expression affects surface hydrophobicity The surface hydrophobicity of GAS has been shown to influence the adherence to abiotic surfaces. The presence of pili [13], M and M-like proteins, and lipoteichoic acid contributes to cell surface hydrophobic properties [12, 35], which in turn may influence biofilm formation by GAS. Here, we have investigated the contribution of Scl1 to surface hydrophobicity of M41-, M28-, and M1-type GAS strains using a modified hexadecane binding assay [12, 36, 37]. As shown in Table 1, the M28-type GAS strain MGAS6143 gave the highest actual hydrophobicity value of 94.3 ± 0.73, followed by the M41-type strain MGAS6183 (92.6 ± 0.86). In contrast, the overall surface hydrophobicity of the M1-type GAS strain MGAS5005 (80.3 ± 0.89) was significantly lower compared to both M28 and M41 strains (P ≤ 0.001 for each comparison). Inactivation of scl1.