Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, CeLS building # 03-05, 28 Medical Drive, Singapore 117597, Singapore.
Microbes Infect. 2010 Mar;12(3):238-45. doi: 10.1016/j.micinf.2009.12.002. Epub 2009 Dec 11.
Polysaccharide capsules contribute to the pathogenesis of many bacteria species by providing resistance against various defense mechanisms. The production of a capsule in Bordetella pertussis, the etiologic agent of whooping cough, has remained controversial; earlier studies reported this pathogen as a capsulated microorganism whereas the recent B. pertussis genome analysis revealed the presence of a truncated capsule locus. In this work, using transmission electron microscopy and immunostaining approaches, we provide a formal evidence for the presence of an intact microcapsule produced at the surface of both laboratory strain and clinical isolates of B. pertussis. In agreement with previous studies, we found that the capsule is optimally produced in avirulent phase. Unexpectedly, the presence of the capsule was also detected at the surface of virulent B. pertussis bacteria. Consistently, a substantial transcriptional activity of the capsule operon was detected in virulent phase, suggesting that the capsular polysaccharide may play a role during pertussis pathogenesis. In vitro assays indicated that the presence of the capsule does not affect B. pertussis adherence to mammalian cells and does not further protect the bacterium from phagocytosis, complement-mediated killing or antimicrobial peptide attack.
多糖荚膜有助于许多细菌物种的发病机制，为其提供了对各种防御机制的抵抗力。百日咳博德特氏菌（百日咳的病原体）产生荚膜的情况一直存在争议；早期的研究报告称该病原体为有荚膜的微生物，而最近对博德特氏菌基因组的分析显示，存在一个截断的荚膜基因座。在这项工作中，我们使用透射电子显微镜和免疫染色方法，为博德特氏菌实验室菌株和临床分离株表面存在完整微荚膜提供了正式证据。与之前的研究一致，我们发现荚膜在无毒力阶段最佳生成。出乎意料的是，在毒力博德特氏菌细菌的表面也检测到了荚膜的存在。一致地，在毒力阶段检测到荚膜操纵子的大量转录活性，表明荚膜多糖可能在百日咳发病机制中发挥作用。体外试验表明，荚膜的存在并不影响博德特氏菌对哺乳动物细胞的黏附，也不能进一步保护细菌免受吞噬作用、补体介导的杀伤或抗菌肽的攻击。
