FIGURE 8.

Lack of CdhA abrogates GAS antiphagocytic function by down-regulating the M protein expression and capsule formation. A, phagocytic index of M1-WT, M1ΔCdhA, M1CdhAΔC55, and M1ΔEmm. The phagocytic index was measured as a multiplication factor (M.F.), indicating the ability of the GAS strain to multiply in the whole human defibrinated blood as described under “Experimental Procedures.” M1ΔEmm lacks the antiphagocytic M protein encoded by the emm1 gene and was used as positive control (13). B, quantitative real-time PCR to determine emm1-specific mRNA in the late log phase culture (growth level III) of M1-WT, M1ΔCdhA, and M1CdhAΔC55 GAS strains in comparison with the internal control gene (proS)-specific mRNA. C, Western blot analysis to determine the expression of the M-protein in the (i) culture supernatants and (ii) cell wall extracts of early (I), middle (II), and late (III) log phase-grown cultures of M1-WT (lane 1), M1ΔCdhA (lane 2), and M1CdhAΔC55 (lane 3) strains using the Emm1-reactive 10B6 monoclonal antibody (33). D, comparison of hyaluronic acid contents of the mutant M1ΔCdhA, M1CdhAΔC55, M1ΔCdhA::cdhA, and M1-WT::cdhA strains with the wild-type M1SF370 (M1-WT) GAS strains. Vertical bars represent mean ± S.E. (error bars) of three independent experiments. *, p < 0.001.