Xu Bin, Pei Xiaomeng, Su Yiqi, Ma Zhe, Fan Hongjie
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, China.
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, China Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou 225009, China.
FEMS Microbiol Lett. 2016 Aug;363(16). doi: 10.1093/femsle/fnw164. Epub 2016 Jul 7.
Direct interaction between pathogens and host cells often is a prerequisite for colonization, infection and dissemination. Regulated production of capsular polysaccharide (CPS), which is made of hyaluronic acid, is essential for the pathogenicity of Streptococcus equi subsp. Zooepidemicus (SEZ). Here, we constructed a CPS-deleted mutant and analyzed it along with the parental wild-type strain in attachment and invasion of mammalian epithelial and endothelial cell lines. The CPS-deleted mutant exhibited significant increase in adherence and invasion by several orders of magnitude compared with the wild-type strain through quantitative analysis and electron microscopy observation. After the wild-type strain was recovered from invaded cells, its morphology was analyzed by visual methods and scanning electron microscopy, which revealed that its capsule was almost completely absent. Capsule measurements showed a similar result in which CPS production was nearly attenuated to the same extent as in the CPS-deleted mutant. qPCR assays revealed a marked reduction in the transcriptional levels of the CPS biosynthesis genes, has operon. Moreover, the repression in capsular production was stable inheritance. Our findings indicate that SEZ is a facultative intracellular bacterium, capsule attenuation in SEZ contributes to attachment and invasion in interactions with host cells, and the active regulation of capsule breakdown is controlled by SEZ during internalization.
病原体与宿主细胞之间的直接相互作用通常是定植、感染和传播的先决条件。由透明质酸组成的荚膜多糖（CPS）的调控产生对于马链球菌兽疫亚种（SEZ）的致病性至关重要。在此，我们构建了一个缺失CPS的突变体，并将其与亲本野生型菌株一起分析了对哺乳动物上皮和内皮细胞系的黏附与侵袭情况。通过定量分析和电子显微镜观察，与野生型菌株相比，缺失CPS的突变体在黏附和侵袭方面表现出显著增加，幅度达几个数量级。从侵袭细胞中回收野生型菌株后，通过视觉方法和扫描电子显微镜对其形态进行分析，结果显示其荚膜几乎完全缺失。荚膜测量显示出类似结果，即CPS产生几乎与缺失CPS的突变体一样减弱到相同程度。qPCR分析显示CPS生物合成基因（has操纵子）的转录水平显著降低。此外，荚膜产生的抑制具有稳定遗传性。我们的研究结果表明，SEZ是一种兼性胞内细菌，SEZ中的荚膜减弱有助于其在与宿主细胞相互作用中的黏附和侵袭，并且在内化过程中，SEZ对荚膜分解的主动调控发挥着作用。
