Department of Bacteriology, Animal and Plant Health Agency, Addlestone, UK.
School of Veterinary and Life Sciences, Murdoch University, Perth, Australia.
Vet Res. 2019 Mar 7;50(1):21. doi: 10.1186/s13567-019-0639-x.
Brachyspira (B.) hyodysenteriae is widespread globally, and can cause mucohaemorrhagic colitis (swine dysentery, SD) with severe economic impact in infected herds. Typical strains of B. hyodysenteriae are strongly haemolytic on blood agar, and the haemolytic activity is believed to contribute to virulence in vivo. However, recently there have been reports of atypical weakly haemolytic isolates of B. hyodysenteriae (whBh). In this study, 34 European whBh and 82 strongly haemolytic isolates were subjected to comparative genomic analysis. A phylogenetic tree constructed using core single nucleotide polymorphisms showed that the whBh formed a distinct sub-clade. All eight genes previously associated with haemolysis in B. hyodysenteriae were present in the whBh. No consistent patterns of amino acid substitutions for all whBh were found in these genes. In contrast, a genome region containing six coding sequences (CDSs) had consistent nucleotide sequence differences between strongly and whBh isolates. Two CDSs were predicted to encode ABC transporter proteins, and a TolC family protein, which may have a role in the export of haemolysins from B. hyodysenteriae. Another difference in this region was the presence of three CDSs in whBh that are pseudogenes in strongly haemolytic isolates. One of the intact CDSs from whBh encoded a predicted PadR-like transcriptional repressor that may play a role in repression of haemolysis functions. In summary, a sub-clade of whBh isolates has emerged in Europe, and several genomic differences, that potentially explain the weakly haemolytic phenotype, were identified. These markers may provide targets for discriminatory molecular tests needed in SD surveillance.
短螺旋体（Brachyspira）hyodysenteriae 广泛分布于全球，可引起黏液脓性出血性结肠炎（猪痢疾，SD），给受感染的畜群造成严重的经济损失。典型的 B. hyodysenteriae 菌株在血琼脂上具有强烈的溶血活性，并且这种溶血活性被认为有助于体内的毒力。然而，最近有报道称存在非典型的弱溶血分离株 B. hyodysenteriae（whBh）。在这项研究中，对 34 株欧洲 whBh 和 82 株强溶血分离株进行了比较基因组分析。使用核心单核苷酸多态性构建的系统发育树表明，whBh 形成了一个独特的亚群。以前与 B. hyodysenteriae 溶血相关的 8 个基因都存在于 whBh 中。在这些基因中，没有发现所有 whBh 的一致的氨基酸取代模式。相比之下，一个包含六个编码序列（CDS）的基因组区域在强和 whBh 分离株之间存在一致的核苷酸序列差异。两个 CDS 预测编码 ABC 转运蛋白，以及一种 TolC 家族蛋白，这可能在 B. hyodysenteriae 溶血素的输出中起作用。该区域的另一个差异是，whBh 中存在三个 CDS，而在强溶血分离株中这些 CDS 是假基因。whBh 中的一个完整 CDS 编码了一个预测的 PadR 样转录阻遏物，它可能在抑制溶血功能中起作用。总之，欧洲已经出现了一个 whBh 分离株的亚群，并且确定了一些可能解释其弱溶血表型的基因组差异。这些标记可能为 SD 监测所需的有区别的分子检测提供靶标。
