Effect of Oxidative and Nitroxidative stress on Bacterial survival under various oxygen tension

尽管唾液和口腔中存在杀菌因子和活化的中性粒细胞，但包括变形链球菌在内的大量细菌仍生活在人类受试者的口腔中。由于口服一氧化氮和相关代谢物的浓度相当高，我们研究了一氧化氮和相关化合物对大肠杆菌和变形杆菌代谢的影响。与大肠杆菌不同，变形杆菌利用两种NADH氧化酶（Nox-1和2）将分子氧代谢为H_2O_2，然后再代谢为H_2O。化学发光和电子顺磁共振的动力学分析表明，缺乏Nox-1、2和AhpC的突变s.t amans的野生型和未敲除种通过依赖Nox-1的途径产生超氧自由基。虽然NO对变形s.t ans的耗氧量没有明显影响，但它增加了免疫反应性硝基酪氨酸蛋白的细胞水平，并抑制了它们的增殖，特别是在低氧张力下。然而，在大气条件下，NO不能抑制s.a mutans的增殖。此外，还发现S.mutans可以从亚硝酸盐中产生NO。这些结果表明，在富含杀菌代谢物和活化中性粒细胞的口腔中，超氧化物和NO的产生对变形链球菌的存活至关重要。

Despite the presence of bactericidal factors and activated neutrophils in saliva and the oral cavity, large numbers of bacteria including S.mutans are living in the oral cavity of human subjects. Because oral concentrations of NO and related metabolites are fairly high, we examined the effect of NO and related compounds on the metabolism of E.coli and S.mutans. Unlike E.coli, S.mutans metabolizes molecular oxygen to H_2O_2 and then to H_2O by using two types of NADH oxidases (Nox-1 and 2). Kinetic analysis using chemiluminescence and electron paramagnetic resonance methods revealed that the wild-type but not knock out species of S.mutans lacking Nox-1, 2 and AhpC generated the superoxide radical via Nox-1-dependent pathway. Although NO did not appreciably affect the oxygen consumption by S.mutans, it increased cellular levels of immunoreactive nitrotyrosyl proteins and inhibited their proliferation particularly under low oxygen tensions. Under air atmospheric conditions, however, NO failed to inhibit the proliferation of S.mutans. Moreover, S.mutans was found to generate NO from nitrite. These results indicate that generation of superoxide and NO is critically important for the survival of S.mutans in the oral cavity enriched with bactericidal metabolites and activated neutrophils.