There was no obvious different in the growth rate of strains SC-19 and ΔperR, but the amount of methionine utilization in the mutant was increased by 25.13% compared to the wild type in cells grown to late-log phase (Figure 5A). These data indicated that the derepression of metQIN led to increased accumulation of methionine in
strain ΔperR. Figure 5 Roles of methionine in the H 2 O 2 resistance. (A) The amount of uptaken methionine in the wild type (WT) and ΔperR in cells grown to late-log phase. (B) The effects of the methionine to H2O2 resistance. Survival rates of wild-type (WT) and ΔperR in CDM with 5 mM of H2O2 challenge for 30 min. 0, 10 and 100 mg/l of methionine were added in the methionine-free basal CDM respectively. To investigate the role of methionine in oxidative stress, the H2O2 sensitivity of strains in CDM with different GS-7977 in vivo concentrations of methionine was tested. As shown in Figure 5B, strain SC-19 showed the lowest survival
rate in CDM lacking methionine, and the survival rates were increased when methionine Fosbretabulin molecular weight was added. The same phenomenon was observed in strain ΔperR, except that ΔperR showed higher survival rates at every methionine concentration. These results indicated that the resistance to H2O2 in S. suis was related to methionine. Role of PerR in pathogenicity in S. Suis An experimental infection model in mice was designed to assess the role of PerR in pathogenicity. In the wild-type group, all of the mice presented severe clinical signs associated with septicemia and septic shock during the first day post-infection and then died from septicemia in this group. In contrast, the mice in the ΔperR group presented with partial clinical signs, three of eight infected mice survived during 1 dpi, and finally one Carbachol mouse was
alive at 7 dpi. Thus, as previously report [25], the mutant strain ΔperR was slightly attenuated in pathogenicity according to survival rate and clinical signs. To investigate the reason of the reduced pathogenicity in perR mutant, mice were intraperitoneally infected with the same dose of SC-19 and ΔperR. Bacteria were recovered from blood, lung, brain and spleen. At 7 dpi, the numbers of ΔperR harvested from blood and each tissue were significantly decreased compared to those of the wild-type strain. At 11 dpi, the ΔperR was nearly cleared from mice, but the wild-type strain could still be recovered (Table 2). Statistical significance of the difference was determined by student t-test. The result suggested that the viability of perR mutant was reduced in the host. Table 2 Survival of SC-19 and ΔperR in different organs in mice Source Strain Bacteria recovered from blood and tissues (×105 CFU)a 4 dpi 7 dpib 11 dpib Blood SC-19 4.49 ± 3.24 2.37 ± 1.71 0.44 ± 0.04 Δ perR 4.10 ± 2.41 0.09 ± 0.05 0 Lung SC-19 4.22 ± 1.45 1.48 ± 0.11 1.03 ± 1.59 Δ perR 1.66 ± 1.11 0.07 ± 0.04 0 Brain SC-19 5.07 ± 3.07 1.42 ± 0.
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