Institute of Medical Microbiology and Hospital Hygiene, University of Ulm, Ulm, Germany.
PLoS One. 2013 Apr 4;8(4):e60160. doi: 10.1371/journal.pone.0060160. Print 2013.
S. agalactiae (group B streptococci, GBS) is a major microbial pathogen in human neonates and causes invasive infections in pregnant women and immunocompromised individuals. The S. agalactiae β-hemolysin is regarded as an important virulence factor for the development of invasive disease. To examine the role of β-hemolysin in the interaction with professional phagocytes, the THP-1 monocytic cell line and human granulocytes were infected with a serotype Ia S. agalactiae wild type strain and its isogenic nonhemolytic mutant. We could show that the nonhemolytic mutants were able to survive in significantly higher numbers than the hemolytic wild type strain, in THP-1 macrophage-like cells and in assays with human granulocytes. Intracellular bacterial multiplication, however, could not be observed. The hemolytic wild type strain stimulated a significantly higher release of Tumor Necrosis Factor-α than the nonhemolytic mutant in THP-1 cells, while similar levels of the chemokine Interleukin-8 were induced. In order to investigate bacterial mediators of IL-8 release in this setting, purified cell wall preparations from both strains were tested and found to exert a potent proinflammatory stimulus on THP-1 cells. In conclusion, our results indicate that the β-hemolysin has a strong influence on the intracellular survival of S. agalactiae and that a tightly controlled regulation of β-hemolysin expression is required for the successful establishment of S. agalactiae in different host niches.
无乳链球菌（B 群链球菌，GBS）是人类新生儿的主要微生物病原体，可引起孕妇和免疫功能低下者的侵袭性感染。无乳链球菌β-溶血素被认为是导致侵袭性疾病发展的重要毒力因子。为了研究β-溶血素在与专业吞噬细胞相互作用中的作用，我们用血清型 Ia 无乳链球菌野生型菌株及其同源非溶血突变株感染 THP-1 单核细胞系和人粒细胞。我们发现，非溶血突变株在 THP-1 巨噬样细胞和人粒细胞中比溶血野生型菌株更能以更高的数量存活，但是不能观察到细胞内细菌的增殖。溶血野生型菌株在 THP-1 细胞中诱导的肿瘤坏死因子-α释放量明显高于非溶血突变株，而趋化因子白细胞介素-8 的水平相似。为了研究这种情况下细菌介导白细胞介素-8 释放的机制，我们测试了两种菌株的纯化细胞壁制剂，发现它们对 THP-1 细胞具有很强的促炎刺激作用。总之，我们的结果表明，β-溶血素对无乳链球菌的细胞内存活有很大影响，并且β-溶血素表达的严格调控是无乳链球菌在不同宿主环境中成功定植所必需的。
