Lecture 11: Intracellular Pathogens Flashcards
Rickettsia, Chlamydia
Where do extracellular infections occur?
In interstitial space, blood, lymph, and epithelial surfaces.
Where do intracellular infections occur?
In the cytoplasm or within vesicles inside host cells.
What are the two types of intracellular pathogens?
Obligate and facultative intracellular pathogens.
Why do obligate intracellular bacteria have smaller genomes?
They depend on the host cell for survival, so they have lost unnecessary metabolic pathways.
Give three examples of obligate intracellular bacterial pathogens.
Chlamydia spp., Rickettsia spp., Coxiella spp.
Give three examples of facultative intracellular bacterial pathogens.
Escherichia coli, Yersinia pestis, Shigella flexneri.
What are the advantages of an intracellular lifestyle for pathogens?
They evade host immune responses and benefit from a stable environment within the host.
What the main challenges for intracellular pathogens?
Entering host cells and escaping after replication.
How do Rickettsia and Shigella escape macrophage destruction?
They secrete exotoxins to disrupt the phagosome membrane and escape into the cytoplasm.
How do Salmonella, Mycobacterium tuberculosis, and Coxiella survive in macrophages?
They resist destruction by producing protective virulence factors and replicating in low-pH environments like the phagolysosome.
How do Mycobacterium tuberculosis and Chlamydia evade destruction in macrophages?
They prevent fusion of the vacuole with lysosomes, avoiding degradation.
How do intracellular pathogens spread within host tissues?
By manipulating the actin cytoskeleton to move within the cytoplasm or between adjacent cells.
What are the mechanisms intracellular pathogens use to exit host cells?
Cytolysis, actin-based protrusion, budding, extrusion, expulsion, pyroptosis, and apoptosis.
Why is cytolysis a risky exit strategy for pathogens?
It triggers a strong immune response.
How does escape by process apoptosis benefit intracellular pathogens?
It allows the pathogen to escape without causing inflammation.
What type of bacteria are Rickettsia?
Small, Gram-negative, obligate intracellular bacteria with reduced genomes.
Why do Rickettsia have a unique genome?
A large portion is non-functional, and it is genetically similar to human mitochondrial DNA.
How is Rickettsia rickettsii transmitted, and what disease does it cause?
It is transmitted by tick bites and causes Rocky Mountain Spotted Fever.
What is a characteristic symptom of Rocky Mountain Spotted Fever?
A rash with swelling and leakage of serous fluid from infected areas.
How is Rickettsia prowazekii transmitted, and what disease does it cause?
It is transmitted by rats and fleas, often in unsanitary, crowded conditions (e.g., wartime) and causes epidemic typhus.
How do Rickettsia escape from host cells?
R. prowazekii causes cell lysis, while R. rickettsii uses actin-based protrusion.
What disease does Chlamydia trachomatis cause?
Trachoma (eye disease) and various sexually transmitted infections (STIs).
How does trachoma cause blindness?
It deforms the eyelid, causing eyelashes to turn inward and scar the cornea over time.
How is trachoma spread, and how can it be prevented?
It is associated with poor hygiene and can be reduced with improved sanitation.
What is unique about the Chlamydia cell wall?
It has very little peptidoglycan but contains a high-protein layer with cysteine-rich proteins for strength.
What are the two forms in the Chlamydia life cycle?
Elementary bodies (infectious form) and reticulate bodies (replicative form).
What happens to Chlamydia once inside a host cell?
It differentiates into the metabolically active reticulate body form, replicates, and then converts back to the infectious elementary body before exiting the cell.
