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What are the three general mechanisms that microbial pathogens use to invade human cells?
Interaction with host surface receptors (Listeria), 2. Injection of bacterial effectors into host cytosol (Salmonella), 3. Active penetration into host cell (Toxoplasma).
How does Listeria monocytogenes traverse the intestinal barrier?
By using a protein adhesin called InlA to interact with E-cadherin receptors on human cells, leading to internalization.
What does InlA do?
InlA interacts with E-cadherin on host cells to mediate the internalization of Listeria.
What is the consequence of Listeria infection?
It can lead to meningitis and abortion of the fetus, particularly in immunocompromised individuals.
How does Listeria monocytogenes spread once internalized?
It can exit the phagosome and enter the cytoplasm of the cell, then move to adjacent cells via an actin tail.
What general role does invasion play for microbial pathogens?
Access to a suitable environment for growth, protection from host antibodies, and traversal of anatomical barriers.
What distinguishes the internalization process of Listeria from that of Salmonella?
Listeria internalization involves localized polymerization of actin, while Salmonella uses large-scale remodeling of the host cell surface (ruffling).
What provides the mechanism for Salmonella's internalization into cells?
Injection of bacterial effector proteins into the host cytosol, manipulating human protein functions.
What type of pathogen is Salmonella?
Salmonella is a Gram-negative food-borne pathogen that causes gastroenteritis and typhoid fever.
What is the incidence of Salmonellosis in the USA?
Approximately 1.4 million cases per year.
How does Salmonella use the type 3 secretion system?
It injects effector proteins into human cells to activate human proteins that stimulate actin polymerization.
What proteins regulate the actin cytoskeleton during Salmonella infection?
Small G proteins of the Rho family, including Rac1 and Cdc42.
What is the function of CDC42 in host cells?
When activated, CDC42 stimulates actin polymerization and formation of cellular protrusions.
What is the role of the bacterial protein SopE?
SopE functions as a guanine nucleotide exchange factor (GEF) to activate host G proteins, boosting actin polymerization.
What mechanism does Toxoplasma gondii use to enter host cells?
Active penetration, utilizing its own motility rather than manipulating host cell mechanisms.
What is the primary host for Toxoplasma gondii?
The house cat, where Toxoplasma reproduces and sheds oocysts.
How can humans become infected with Toxoplasma gondii?
Through ingestion of tissue cysts in undercooked meat or oocysts from cat feces.
What behavioral change does Toxoplasma induce in infected rodents?
Infected rodents may lose their fear of cat odor, increasing the chance of being preyed upon by cats.
What is gliding motility in Toxoplasma?
A mechanism that allows Toxoplasma to move along the intestinal epithelium and enter host cells.
What cytoskeleton components are involved in the gliding motility of Toxoplasma?
Actin and microtubule cytoskeletons are utilized by the parasite for movement.
How does the actin cytoskeleton assist Toxoplasma during invasion?
The actin cytoskeleton of Toxoplasma interacts with host cell receptors, allowing it to exert force and penetrate host cells.
What is the function of myosin A in Toxoplasma invasion?
Myosin A interacts with the actin cytoskeleton to produce a power stroke that helps push the parasite into the host cell.
What is the difference between the internalization strategies of Toxoplasma and Salmonella?
Toxoplasma internally penetrates via gliding motility, while Salmonella manipulates host cell functions through injected effector proteins.
How does Listeria utilize the host's cytoskeletal system for invasion?
By inducing localized changes to the host's F-actin cytoskeleton around itself for internalization.
What is meant by 'treadmilling' in the context of actin dynamics?
The process in which actin filaments grow at one end and dissociate at the other, driving cell motility.
Why is internalization beneficial for Salmonella and Listeria?
It provides access to suitable growth niches, protection from host immune responses, and traversal of anatomical barriers.
What characterizes the structure of microtubules?
Microtubules are made of α- and β-tubulin and have a diameter of approximately 25 nm; they are important for cell structure and movement.
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