AED - Infection I & II - Week 3 Flashcards
List 5 mechanisms of tissue injury with bacterial infections.
Release of enzymes that aid in invsaion and tissue breakdown
Release of exotoxins which inhibit cellular functions
Release of endotoxins that have detrimental effects on cell function
Collateral tissue damage
Initiation of later hypersensitivity response
Which gram type generally releases exotoxins and endotoxins?
Endo - gram negative
Exo - gram positive
List 4 mechanisms of damage in viral infections.
Avoids immune surveillance by entering cells and using machinery to self-replicate and burst through the membrane
Viral replication changes cell’s antigenic properties invoking inflammatory/immunes responses
Intracellular replication disrupts cellular function
Are most bacteria able to penetrate an intact cornea or conjunctiva?
No
How long would P. auruginosa proteases take to penetrate an intact epithelium? What is this usually prevented by (3)?
Needs 3 hours
Prevented by lid action, tear flow and tear antibacterials
What happens if bacteria gain access to basolateral surfaces of the epithelium?
Much easier to disrupt junctional complexes
Some bacteria can bind and enter ocular epithelial cells. To what purpose? Give an example.
To protect themselves from the inflammatory response.
P. auruginosa
Describe the early histopathology of a bacterial infection.
Compromised epithelium allows bacteria invasion - exotoxins aid this process
Replication in the stroma and further exotoxin release damages overlying epithelium - stimulates inflammatory response
Neutrophil enzymes and bacterial exotoxins cause further tissue damage
What cell coordinate further inflammatory cell activity late in infections?
Lymphocytes
Describe how daytime contact lens wear can increase susceptibility to infection (5).
Contact lenses and an immobile tear film shield bacteria from lip sweeping and tear film protective action
Chronic mild hypoxia of the corneal epithelium promotes bacterial adhesion to the epithelium
How can overnight contact lenses increase susceptibility to bacterial infection?
Alters tear levels of pro-inflammatory cytokines - may promote a pro-inflammatory environment
The migration of which cell is stimulated with extended wear contact lenses? To which part of the eye do they migrate? Explain what kind of cells they are and why this migration is so significant.
Langerhan’s cells migrate to the central cornea
They are APCs, so if an infection occurs, inflammation is more aggressive than normal
What does chronic dry eye induce? Does dry eye increase susceptibility to ocular infection? Explain.
Chronic dry eye induces epithelial apoptosis
This can cause epithelial erosion, improving bacterial adhesion
Reduced tears results in reduced antibacterial activity
Briefly describe the model of pathogenesis for corneal bacterial infection (5).
Early destruction of opithelium and bacterial proliferation
Neutrophil chemotaxis from limbal vessels
Release of proteases and ROS
Chemotaxis of lymphocytes - inflammatory cell activity increases
Corneal perforation
What are protozoan infections characterised by?
Extreme pain
List the two forms of acanthamoeba.
Trophozoites (motile form)
Encysted (cellulose wall)
How are acanthamoeba identified?
Confocal microscopy
What are the most common inflammatory cells in an acanthamoeba infection and what is usually seen when this happens?
Neutrophils - a ring infiltrate can be seen
What do acanthamoeba preferentially target?
Corneal nerves
