Pettygrove Brian A, Nygaard Tyler K, Borgogna Timothy R, Malachowa Natalia, Gaur Gauri, Salo Shannon E, Pallister Kyler B, Burroughs Owen, Robinson Cassandra, Gao Annika, Sturdevant Daniel E, Ricklefs Stacy, DeLeo Frank R, Otto Michael, Stewart Philip S, Voyich Jovanka M
Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717.
Department of Microbiology & Cell Biology, Montana State University, Bozeman, MT 59717.
Proc Natl Acad Sci U S A. 2025 May 20;122(20):e2412447122. doi: 10.1073/pnas.2412447122. Epub 2025 May 13.
() is a frequent culprit in implant-associated infections and employs many virulence factors to escape killing by the host immune system. The specific immune evasion strategies used by small aggregates of on a surface, precursors to mature biofilm, are still relatively unknown. Time-lapse confocal microscopy was leveraged to quantify interactions between aggregates and human neutrophils in vitro and identify specific mechanisms of resistance to neutrophil killing. Surface-associated wild-type rapidly formed small biofilm aggregates when grown in human serum. Conversely, aggregation was inhibited when the SaeR/S two-component gene regulatory system was deleted. Wild-type aggregates began to show individual and population-level resistance to neutrophil killing upon reaching sizes of approximately 50 to 75 µm, whereas Δ clusters failed to reach these sizes and were readily cleared. Aggregation of Δ strains was impaired by serum complement, and this inhibition required complement proteins C3 and factor B, but not C4 or C5, suggesting that this activity primarily occurs at the level of the alternative pathway. Several complement-inhibiting genes regulated by SaeR/S were identified that collectively facilitate biofilm aggregate formation in human, but not murine serum. Finally, aggregation of two related opportunistic pathogens, and , was inhibited by serum. These data demonstrate a function of serum complement, the ability to inhibit bacterial aggregation, that is potently blocked by through the production of multiple complement-interfering proteins that are regulated by the SaeR/S system.
（某病原体）是植入物相关感染中常见的罪魁祸首，它利用多种毒力因子来逃避宿主免疫系统的杀灭。在表面形成的小聚集体（成熟生物膜的前体）所采用的具体免疫逃避策略仍相对未知。利用延时共聚焦显微镜在体外定量（某病原体）聚集体与人类中性粒细胞之间的相互作用，并确定对中性粒细胞杀伤的抗性具体机制。表面相关的野生型（某病原体）在人血清中生长时迅速形成小的生物膜聚集体。相反，当SaeR/S双组分基因调控系统缺失时，聚集受到抑制。野生型聚集体在达到约50至75微米大小时开始表现出对中性粒细胞杀伤的个体和群体水平抗性，而Δ聚集体未能达到这些大小并容易被清除。Δ菌株的聚集受到血清补体的损害，这种抑制作用需要补体蛋白C3和因子B，但不需要C4或C5，这表明这种活性主要发生在替代途径水平。鉴定出了几个由SaeR/S调控的补体抑制基因，它们共同促进了在人血清而非鼠血清中的生物膜聚集体形成。最后，两种相关的机会性病原体（另外两种病原体）的聚集受到血清抑制。这些数据证明了血清补体的一种功能，即抑制细菌聚集的能力，而（某病原体）通过产生多种由SaeR/S系统调控的补体干扰蛋白有力地阻断了这种功能。
