Eye infections Flashcards
What is the principle cause of eye infections and why?
S. aureus, due to high carrier rate in humans
What are the four main staphylococcal eye infections?
- Dacryocystitis - inflammation of the lacrimal sac
- Blepharitis - infection of eyelid or sebacious gland
- Conjunctivitis - can be keratoconjuctivitis if corneal involvement
- Endophthalmitis - infection of aqueous or vitreous humor
What are required for keratitis or endophthalmitis?
Some trauma to cornea for keratitis
Ulceration or penetrating injury of cornea or sclera for endophthalmitis
What are three major virulence factors of S. pneumoniae?
- Polysaccharide capsule - primary, avoids complement-mediated phagocytosis and lysis
- Pneumolysin, a membrane-damaging cytolysin related to SLO of S. pyogenes
- Cell wall teichoic acid / peptidoglycan promote inflammation
What is the major way in which S. pneumoniae infects the eyes? What does it cause?
Autoinoculation from upper respiratory tract (touch nose then eyes)
Causes Dacryocystitis, conjunctivitis, and keratoconjunctivitis
What are two other names for S. pneumoniae?
Pneumococcus or diplococcus (gram positive diplococci)
What Lancefield group is S. pneumoniae in?
It is not part of the Lancefield grouping scheme
What biochemical tests are used on S. pneumoniae?
- Capsular serotyping
- Quellung reaction -> capsular swelling induced via mixing with anti-capsule antibodies
- P disk susceptibility testing
What is the primary virulence factor of H. influenzae?
Polysaccharide capsule, which is antiphagocytic and subject to antigenic variation. Has serotypes a-f.
What is the most virulent H. influenzae capsule comprised of? How is the vaccine made for it?
b capsule: contains polyribitol phosphate (PRP)
Hib vaccine made by giving PRP conjugated with diphtheria toxoid or Neisseriae outer membrane protein
Where is H. influenzae found and what does it cause??
Found exclusively in humans, with high carriage rate in upper respiratory tract, most of which lack capsule
Causes same things as S. pneumoniae (just not endopthalmitis or blepharitis)
What is the morphology of H. influenzae?
Gram negative coccobacillus
What special factors are required for the growth of H. influenzae? Why is this relevant?
X factor and V factor (cytochromes), which are blood products. Will grow on chocolate agar but not blood agar (need lysed erythrocytes)
What is the satellite growth test?
Put cytochrome factors X and V on discs which diffuse out into blood agar, H. influenzae will only grow around discs (diagnostic of this pathogen)
What are the three primary virulence factors of P. aeruginosa?
- Exotoxin A
- Elastase
- Adhesin
What does Exotoxin A do and what other toxin does it relate to?
It is an AB cytotoxin, with receptor part and enzymatic part - ADP-ribosylating enzyme which attaches ADP-ribose to host elongation factor 2, killing the cell. Promotes tissue invasion.
Same mechanism as diphtheria toxin
What does elastase do? How does it relate to eye pathology?
Cleaves elastin and human Igs, collagen, and complement
It is the primary cause of corneal perforation in eye infection
What does the P. aeruginosa adhesin require?
Requires trauma (scratch) to adhere to corneal exposed receptors
What is one major risk factor for P. aeruginosa to colonize?
Extended contact lens use (can live in contact lens solution, opportunistic pathogen)