15.4
病原体定植
病原体在宿主组织中的定植是感染性疾病发生发展的关键步骤。多种致病性微生物，包括细菌、真菌、病毒和原生动物，已进化出复杂的策略以附着、侵入并在宿主环境中持续存在。这些机制使病原体能够建立感染、逃避免疫应答，并抵抗抗菌治疗。
与宿主细胞的黏附
在细菌中，定植通常始于黏附于宿主的上皮表面，例如呼吸道或胃肠道的…
许多原核生物和真核生物病原体能够在不立即引发疾病的情况下定植于宿主组织。只有当定植导致组织损伤或宿主发生炎症反应时，才会发生感染。
细菌通过附着于宿主细胞来启动定植。
某些细菌具有菌毛或纤毛，可附着在呼吸道等部位的上皮细胞上。
许多致病菌表达称为黏附素的表面蛋白，这些蛋白有助于增强与宿主细胞的黏附。
附着后，病原体开始在宿主内建立感染。
某些细菌会形成生物膜，从而提供对免疫攻击的防护并产生对治疗的耐药性。
定植后，某些病原体会产生酶（如透明质酸酶或凝固酶），这些酶有助于在感染过程中侵入组织。
某些病原体形成荚膜以掩盖抗原结构，并防止被免疫细胞吞噬。
或者，抗原变异使某些病原体能够修饰其表面蛋白，以逃避免疫反应并延长定植时间。
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Q1: How do bacteria initially attach to host cells during colonization?
Bacteria initiate colonization by using specialized structures like pili or fimbriae to anchor to epithelial cells in areas such as the respiratory tract. Many pathogenic bacteria also express surface proteins called adhesins, which strengthen attachment by recognizing and binding to extracellular matrix components or cell surface molecules on host cells.
Q2: What is the difference between colonization and infection?
Colonization occurs when pathogens attach to and establish themselves within host tissues without immediately causing disease. Infection develops only when colonization leads to tissue damage or triggers a host inflammatory response. Many prokaryotic and eukaryotic pathogens can colonize tissues for extended periods before progressing to active infection.
Q3: How do biofilms protect bacteria from immune attacks?
Biofilms are structured communities of bacteria encased in a self-produced extracellular matrix that provides enhanced protection against phagocytosis and antimicrobial agents. This protective structure significantly increases pathogen persistence within the host. Quorum sensing, a form of bacterial communication via signaling molecules, regulates biofilm formation and virulence factor expression.
Q4: What enzymes do pathogens produce to facilitate tissue invasion?
Pathogens produce enzymes such as hyaluronidase and coagulase to facilitate tissue invasion. Hyaluronidase breaks down hyaluronic acid in connective tissues, aiding tissue penetration, while coagulase induces fibrin clot formation that may shield bacteria from immune cells. These enzymatic secretions help pathogens establish deeper infections within host tissues.
Q5: How do bacterial capsules help pathogens evade the immune system?
Bacterial capsules are composed of polysaccharides that mask antigenic cell surface components, preventing recognition and phagocytosis by immune cells. This immune evasion strategy allows pathogens to avoid detection and elimination. Capsules represent one of several mechanisms pathogens use to establish persistent infections and resist host defenses.
Q6: What is antigenic variation and how does it extend colonization?
Antigenic variation is a mechanism in which pathogens alter surface protein structures to escape recognition by host antibodies. This strategy allows prolonged colonization and chronic or relapsing infections. Pathogens such as Neisseria gonorrhoeae and Trypanosoma brucei are well known for using antigenic variation to evade immune detection and maintain persistent infections.
Q7: How do intracellular pathogens like Listeria monocytogenes avoid immune surveillance?
Some bacteria adopt an intracellular lifestyle to circumvent immune surveillance by invading host cells and exploiting the host cytoskeleton. These pathogens use actin-based motility structures, commonly termed actin rockets, to propel themselves and enable direct cell-to-cell transmission. This intracellular movement minimizes exposure to extracellular immune defenses and represents a key determinant of bacterial pathogenicity and virulence.