regulation of entry of bacterium into host cell

Definition

Target type: biologicalprocess

Any process that modulates the frequency, rate or extent of entry of bacterium into host cell. [GOC:obol]

The entry of bacteria into host cells is a complex and tightly regulated process that is crucial for bacterial pathogenesis. This process involves a series of steps, starting with the initial interaction of the bacterium with the host cell surface, followed by adherence, and culminating in internalization. The specific mechanisms employed by bacteria to gain entry into host cells are diverse and vary greatly between different bacterial species. However, several common themes emerge:

**1. Adhesion:** The first step in bacterial entry is adhesion to the host cell surface. This process is mediated by specific bacterial adhesins that bind to complementary receptors on the host cell membrane. These adhesins can be located on the bacterial surface, such as pili, fimbriae, or capsules, or they can be secreted proteins. Adhesins often bind to specific host cell receptors, such as integrins, cadherins, or glycoproteins.

**2. Invasion:** Once attached to the host cell, bacteria can employ various strategies to gain entry. Some bacteria use a **trigger mechanism** to induce host cell internalization. This involves bacterial secretion of effector proteins that alter host cell signaling pathways, leading to cytoskeletal rearrangements and engulfment of the bacterium by the host cell. Other bacteria utilize a **zipper mechanism**, where bacterial surface proteins interact directly with host cell receptors, triggering localized cytoskeletal rearrangements and invagination of the host cell membrane, ultimately engulfing the bacterium.

**3. Internalization:** After invasion, bacteria are internalized within a membrane-bound vacuole called a phagosome. The fate of the bacteria within the phagosome depends on the specific bacterial species and the host cell type. Some bacteria escape the phagosome and enter the host cell cytoplasm, where they can replicate and spread. Others remain within the phagosome and establish a niche for replication or remain dormant.

**Specific Examples:**

* **Salmonella:** This bacterium utilizes a **trigger mechanism** involving the secretion of effector proteins through a Type III secretion system. These effector proteins manipulate the host cell actin cytoskeleton, leading to the formation of membrane ruffles and eventual engulfment of the bacterium.
* **Shigella:** This bacterium employs a **zipper mechanism** using a surface protein called IpaB, which interacts with host cell receptors and triggers localized cytoskeletal rearrangements, allowing the bacterium to enter the host cell.
* **Mycobacterium tuberculosis:** This bacterium is able to survive and replicate within the phagosome, preventing its fusion with lysosomes and avoiding degradation.

**Regulation:**

The regulation of bacterial entry is a complex process involving multiple factors, including:

* **Bacterial factors:** Bacterial genes encoding adhesins, invasion factors, and effector proteins are often regulated by environmental cues such as temperature, pH, and the presence of host cell factors.
* **Host cell factors:** Host cell receptors, signaling pathways, and the immune system all play a role in regulating bacterial entry.
* **Environmental factors:** Factors such as nutrient availability, oxygen tension, and the presence of antibiotics can also influence bacterial entry.

**Consequences:**

The successful entry of bacteria into host cells is essential for the establishment of infection and disease. Bacteria that are able to gain entry into host cells can evade the immune system, replicate, and spread to other cells, leading to various symptoms and disease manifestations.

**Conclusion:**

The regulation of bacterial entry into host cells is a complex and multifaceted process involving a series of steps and the interplay of bacterial and host cell factors. Understanding this process is crucial for developing effective strategies to prevent and treat bacterial infections.
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