Complement inhibition by Sarcoptes scabiei protects Streptococcus pyogenes - An in vitro study to unravel the molecular mechanisms behind the poorly understood predilection of S. pyogenes to infect mite-induced skin lesions
Fig 3
Scabies mite complement inhibitor SMSB4 reduces the baseline immunity of GAS clinical isolates in fresh blood (A) and promotes the growth of GAS skin strain 88/30 in a dose-dependent manner (B).
Skin strains 88/30, PRS30 (emm cluster D), throat strains PRS8, 5448 (emm cluster A-C) and skin/throat strains PRS55, PRS15 (emm cluster E) (A) or GAS 88/30 only (B) were harvested from mid-log growth phase culture (OD600 0.35). GAS diluted in PBS (1 ×103 cfu/ml) were added into fresh blood pre-treated with either 2 μM (A) or a range of concentrations (B) of either SMSB4 or BSA. After 3 h incubation samples were plated in duplicate on CBAC agar plates and bacteria were enumerated as cfu/ml. The challenge dose of GAS cells in PBS without blood (A) or the challenge dose in blood with GVB2+ buffer (B) was plated simultaneously and the numbers of bacteria grown served as the baseline for normalisation and for calculating the fold difference of bacteria numbers from the experimental samples. Data represent the means ± SEM from three independent experiments. The statistical significance of differences between samples was estimated using two way ANOVA with Tukey’s (A) or Sidak’s (B) multiple comparison test. **, p<0.01; ***, p<0.001; ****, p<0.0001.