Animal Research Institute, School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia.
Vet Microbiol. 2011 Nov 21;153(1-2):150-5. doi: 10.1016/j.vetmic.2011.02.053. Epub 2011 Mar 3.
Swine dysentery (SD) results from infection of the porcine large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Recently the genome of virulent Australian B. hyodysenteriae strain WA1 was sequenced, and a 36 kilobase (kb) circular plasmid was identified. The plasmid contained 31 genes including six rfb genes that were predicted to be involved with rhamnose biosynthesis, and others associated with glycosylation. In the current study a set of PCRs was developed to amplify portions of nine of the plasmid genes. When used with DNA extracted from virulent strain B204, PCR products were generated, but no products were generated with DNA from avirulent strain A1. Analysis of the DNA using pulsed field gel electrophoresis (PFGE) identified a plasmid band in strains WA1 and B204, but not in strain A1. These results demonstrate that strain A1 does not contain the plasmid, and suggests that lack of the plasmid may explain why this strain is avirulent. To determine how commonly strains lacking plasmids occur, DNA was extracted from 264 Australian field isolates of B. hyodysenteriae and subjected to PCRs for three of the plasmid genes. Only one isolate (WA400) that lacked the plasmid was identified, and this absence was confirmed by PFGE analysis of DNA from the isolate and further PCR testing. To assess its virulence, 24 pigs were experimentally challenged with cultures of WA400, and 12 control pigs were challenged with virulent strain WA1 under the same conditions. Significantly fewer (P=0.03) of the pigs challenged with WA400 became colonised and developed SD (13/24; 54%) compared to the pigs infected with WA1 (11/12; 92%). Gross lesions in the pigs colonised with WA400 tended to be less extensive than those in pigs colonised with WA1, although there were no obvious differences at the microscopic level. The results support the likelihood that plasmid-encoded genes of B. hyodysenteriae are involved in colonisation and/or disease expression.
猪痢疾由猪大肠内的厌氧螺旋体细菌-短螺旋体属引起。最近，澳大利亚具有毒力的短螺旋体属 WA1 菌株的基因组被测序，并发现了一个 36 千碱基（kb）的环形质粒。该质粒包含 31 个基因，包括 6 个预测与鼠李糖生物合成有关的 rfb 基因和其他与糖基化有关的基因。在本研究中，开发了一组 PCR 来扩增质粒中 9 个基因的部分序列。当使用从毒力菌株 B204 中提取的 DNA 时，会产生 PCR 产物，但使用无毒性菌株 A1 提取的 DNA 则不会产生产物。使用脉冲场凝胶电泳（PFGE）对 DNA 进行分析，发现 WA1 和 B204 菌株中存在质粒带，但 A1 菌株中不存在。这些结果表明，A1 菌株不含有质粒，并且表明缺乏质粒可能是该菌株无毒性的原因。为了确定缺乏质粒的菌株出现的频率，从 264 株澳大利亚田间分离的短螺旋体属提取 DNA，并进行 3 个质粒基因的 PCR。仅鉴定出一个缺乏质粒的分离株（WA400），并通过对分离株的 DNA 进行 PFGE 分析和进一步的 PCR 检测进一步证实了这一点。为了评估其毒性，用 WA400 培养物对 24 头猪进行了实验性攻毒，并用相同条件下的毒力菌株 WA1 对 12 头对照猪进行了攻毒。与感染 WA1 的猪（11/12；92%）相比，用 WA400 攻毒的猪中，明显更少的猪被定植并发生猪痢疾（13/24；54%）（P=0.03）。与感染 WA1 的猪相比，用 WA400 定植的猪的结肠病变范围倾向于更小，但在显微镜下没有明显差异。这些结果支持了短螺旋体属的质粒编码基因参与定植和/或疾病表达的可能性。
