Unique Cell Adhesion and Invasion Properties of Yersinia enterocolitica O:3, the Most Frequent Cause of Human Yersiniosis

Many enteric pathogens are equipped with multiple cell adhesion factors which are important for host tissue colonization and virulence. Y. enterocolitica, a common food-borne pathogen with invasive properties, uses the surface proteins invasin and YadA for host cell binding and entry. In this study, we demonstrate unique cell adhesion and invasion properties of Y. enterocolitica serotype O:3 strains, the most frequent cause of human yersiniosis, and show that these differences are mainly attributable to variations affecting the function and expression of invasin in response to temperature. In contrast to other enteric Yersinia strains, invasin production in O:3 strains is constitutive and largely enhanced compared to other Y. enterocolitica serotypes, in which invA expression is temperature-regulated and significantly reduced at 37°C. Increase of invasin levels is caused by (i) an IS1667 insertion into the invA promoter region, which includes an additional promoter and RovA and H-NS binding sites, and (ii) a P98S substitution in the invA activator protein RovA rendering the regulator less susceptible to proteolysis. Both variations were shown to influence bacterial colonization in a murine infection model. Furthermore, we found that co-expression of YadA and down-regulation of the O-antigen at 37°C is required to allow efficient internalization by the InvA protein. We conclude that even small variations in the expression of virulence factors can provoke a major difference in the virulence properties of closely related pathogens which may confer better survival or a higher pathogenic potential in a certain host or host environment.

诸多肠道病原体均携带多种细胞黏附因子，此类因子在宿主组织定植与毒力发挥过程中至关重要。小肠结肠炎耶尔森菌（Yersinia enterocolitica）是一类常见的食源性侵袭性病原体，其借助表面蛋白侵袭素（invasin）与耶尔森菌黏附素A（YadA）完成宿主细胞的结合与侵入。本研究揭示了作为人类耶尔森菌病（yersiniosis）最常见致病株的小肠结肠炎耶尔森菌O:3血清型菌株所独有的细胞黏附与侵袭特性，并证实此类差异主要源于温度响应下侵袭素功能与表达水平的相关变异。与其他肠道耶尔森菌菌株不同，O:3血清型菌株的侵袭素表达为组成型，且相较于其他小肠结肠炎耶尔森菌血清型显著上调；而其余血清型的invA基因（invA）表达受温度调控，在37℃时会显著降低。侵袭素水平升高源于两处变异：其一为插入序列IS1667（IS1667）插入至invA基因启动子区域，该插入片段包含额外启动子以及RovA与H-NS结合位点；其二为侵袭素激活蛋白RovA发生P98S氨基酸置换，使得该调控蛋白的蛋白水解敏感性降低。研究证实上述两处变异均可影响小鼠感染模型中的细菌定植能力。此外，本研究发现，在37℃条件下，YadA的共表达与O抗原（O-antigen）的下调是InvA蛋白实现高效胞内侵入的必要条件。本研究最终得出结论：即便毒力因子的表达仅存在微小变异，也可导致亲缘关系紧密的病原体在毒力特性上产生显著差异，此类差异或可使病原体在特定宿主或宿主环境中获得更优的生存能力或更高的致病潜能。