Comparative Exoprotein Profiling of Different Staphylococcus epidermidis Strains Reveals Potential Link between Nonclassical Protein Export and Virulence

Staphylococcus epidermidis (SE) includes commensal and pathogenic strains capable of infecting humans and animals. This study reports global exoproteome profiling of bovine mastitis strain PM221 and two human strains, commensal-type ATCC12228 and sepsis-associated RP62A. We identified 451, 395, and 518 proteins from culture supernatants of PM221, ATCC12228, and RP62A, respectively. Comparison of the identified exoproteomes revealed several strain-specific differences related to secreted antigens and adhesins, higher virulence capability for RP62A, and similarities between the PM221 and RP62A exoproteomes. The majority of the identified proteins (∼80%) were predicted to be cytoplasmic, including proteins known to be associated in membrane vesicles (MVs) in Staphylococcus aureus and immunogenic/adhesive moonlighting proteins. Enrichment of MV fractions from culture supernatants and analysis of their protein composition indicated that this nonclassical protein secretion pathway was being exploited under the conditions used and that there are strain-specific differences in nonclassical protein export. In addition, several predicted cell-surface proteins were identified in the culture media. In summary, the present study is the first in-depth exoproteome analysis of SE highlighting strain-specific factors able to contribute to virulence and adaptation.表皮葡萄球菌（Staphylococcus epidermidis，SE）包含可感染人类与动物的共生菌株与致病菌株。本研究针对牛乳腺炎菌株PM221以及两株人类来源菌株（共生型ATCC12228与败血症关联型RP62A）开展了全覆盖分泌蛋白质组（exoproteome）分析，分别从PM221、ATCC12228与RP62A的培养上清液中鉴定出451、395与518种蛋白质。对所鉴定分泌蛋白质组的比较分析显示，不同菌株在分泌型抗原与黏附素方面存在若干菌株特异性差异，RP62A的毒力更强，且PM221与RP62A的分泌蛋白质组具有较高相似性。所鉴定的蛋白质中约80%被预测为胞质蛋白，包括在金黄色葡萄球菌（Staphylococcus aureus）中被证实与膜囊泡（membrane vesicles，MVs）相关的蛋白质，以及具有免疫原性与黏附功能的兼职蛋白（moonlighting proteins）。对培养上清液中的膜囊泡组分进行富集并分析其蛋白质组成，结果表明实验条件下细菌利用了该非经典蛋白质分泌途径，且不同菌株在非经典蛋白质输出方面存在特异性差异。此外，本研究还在培养基中鉴定出若干预测的细胞表面蛋白。综上，本研究是首次针对表皮葡萄球菌开展的深度分泌蛋白质组分析，揭示了可参与毒力形成与环境适应的菌株特异性因子。