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Streptococcus iniae Phosphoglucomutase Is a Virulence Factor and a Target for Vaccine Development

机译：猪链球菌磷酸葡萄糖突变酶是一种毒力因子，是疫苗开发的目标

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Streptococcus iniae represents a major health and economic problem in fish species worldwide. Random Tn917 mutagenesis and high-throughput screening in a hybrid striped bass (HSB) model of meningoencephalitis identified attenuated S. iniae mutants. The Tn917 insertion in one mutant disrupted an S. iniae homologue of a phosphoglucomutase (pgm) gene. Electron microscopy revealed a decrease in capsule thickness and cell wall rigidity, with ΔPGM mutant cells reaching sizes ～3-fold larger than those of the wild type (WT). The ΔPGM mutant was cleared more rapidly in HSB blood and was more sensitive to killing by cationic antimicrobial peptides including moronecidin from HSB. In vivo, the ΔPGM mutant was severely attenuated in HSB, as intraperitoneal challenge with 1,000 times the WT lethal dose produced only 2.5% mortality. Reintroduction of an intact copy of the S. iniae pgm gene on a plasmid vector restored antimicrobial peptide resistance and virulence to the ΔPGM mutant. In analysis of the aborted infectious process, we found that ΔPGM mutant organisms initially disseminated to the blood, brain, and spleen but were eliminated by 24 h without end organ damage. Ninety to 100% of fish injected with the ΔPGM mutant and later challenged with a lethal dose of WT S. iniae survived. We conclude that the pgm gene is required for virulence in S. iniae, playing a role in normal cell wall morphology, surface capsule expression, and resistance to innate immune clearance mechanisms. An S. iniae ΔPGM mutant is able to stimulate a protective immune response and may have value as a live attenuated vaccine for aquaculture.
机译：链球菌代表着全世界鱼类的主要健康和经济问题。脑膜脑炎的混合条纹鲈（HSB）模型中的随机Tn 917 诱变和高通量筛选确定了减毒的 S。 iniae 突变体。 Tn 917 插入一个突变体会破坏 S。葡糖变位酶（ pgm ）基因的iniae 同源物。电子显微镜显示胶囊厚度和细胞壁刚性降低，ΔPGM突变细胞的大小比野生型（WT）大〜3倍。 ΔPGM突变体在HSB血液中的清除速度更快，并且对包括HSB的莫罗那丁在内的阳离子抗菌肽的杀灭作用更为敏感。在体内，ΔPGM突变体在HSB中严重减毒，因为腹膜内攻击的致死剂量是野生型致死剂量的1000倍，仅产生2.5％的死亡率。重新引入完整的 S副本。质粒载体上的Iniae pgm 基因恢复了对ΔPGM突变体的抗菌肽耐药性和毒力。在对中止的感染过程进行分析时，我们发现ΔPGM突变生物最初扩散至血液，大脑和脾脏，但在24 h内被消灭，而没有损害末端器官。 90％至100％的鱼注射了ΔPGM突变体，随后用致死剂量的WT S攻击。 iniae 幸存下来。我们得出结论， pgm 基因是 S中毒力所必需的。 iniae ，在正常细胞壁形态，表面被膜表达以及对先天免疫清除机制的抵抗中起作用。一个 S。 iniae ΔPGM突变体能够刺激保护性免疫反应，并具有作为水产养殖减毒活疫苗的价值。

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