MIIM - Bacteria and Fungi Causing Ocular Infections V - Week 3 Flashcards
Describe the gram stain, shape, and metabolic state of pseudomonas. Does it produce spores? What are its growth requirements?
It is a gram negative rod
Aerobic
Minimal growth requirements
What two pigments are produced by pseudomonas?
Pyocyanin
Fluorescein
What bacteria is the most common cause of contact lens associated keratitis.
Pseudomonas aureginosa
Following eye injury, what bacteria is a common cause of exogenous endophthalmitis?
Pseudomonas aureginosa
Are the outcomes of pseudomonas eye infections good or poor?
Poor
Name 7 means of pathogenesis for pseudomonas.
Adhesion structures, especially good for CL, CL cases
Nutritionally resourceful - ubiquitous
Opportunistic
Induces inflammatory response
Produces exotoxins
Pyocyanin targets many pathways
Has cytotoxic and invasive strains
Name 4 places where pseudomonas could form a biofilm.
CL, CL cases, pipes, and showerheads
Name two specimens that can be used in a suspected pseudomonas infection.
Conjunctival swab
Corneal scraping
What do cultures of pseudomonas look and smell like?
Large colonies which produce blue-green water soluble pigment
Has a distinct sweet ammonia smell
Is pseudomonas oxidase positive or negative?
Positive
What media does pseudomonas grow on?
Basal media like NA
Is pseudomonas aureginosa inherently resistant or susceptible to most antibiotics?
Is resistant to many commonly used antibiotics, and can acquire resistance to others.
What should be done prior to treating pseudomonas with antibiotics?
Susceptibility test
Name 4 ways pseudomonas infections can be prevented.
Preventing CL associated infections by improving cleaning and wearing compliance
Discourage home-made cleaning salines
Using approved and sterile cleansers to remove biofilms
Using sterile CL storage solutions
Name 5 ocular diseases that can be caused by pseudomonas.
Keratitis
Keratoconjunctivitis
Orbital cellulitis
Endophthalmitis
Uveitis
How can orbital cellulitis cause a thrombosis, and is this serious?
If the infection spreads through thin bone, the abcess can pass into the blood stream.
Is life threatening.
Does orbital cellulitis cause proptosis?
It may
Name 4 agents that can cause orbital cellulitis.
Streptococcus pneumoneae
Haemophilus influenzae type b
Staphylococcus aureus
Streptococcus pyogenes
What is the most common cause of orbital cellulitis?
Sinus infection
Define endophthalmitis.
Inflammation of the interior of the eye (inside the globe).
What is the typical cause of endophthalmitis?
Eye surgery or trauma
Is endophthalmitis a minor condition or an emergency?
Emergency
Name 5 symptoms of endophthalmitis.
Progressive vision loss, photophobia, eye pain, red/pink eye, floaters
Name an endogenous source of endophthalmitis. Are these cases common or rare?
Haematogenous spread from a distant source like endocarditis.
These are rare.
Name 3 ways of managing an edophthalmitis infection.
Intravitreal injection of antibiotics - repeated if no response
-systemic antibiotics should be used if the source is endogenous
Vitrectomy in severe cases
Can vision be retained or restored in endophthalmitis cases?
If appropriate care is given, useful vision can be recovered. In severe cases, it may result in the loss of sight or the eye.
Describe the gram stain, shape and metabolic type of bacillus bacteria. Do they produce spores? Where are they found?
They are large gram positive rods
Produce spores
Aerobic or facultative anaerobes
Found in soil and dust
Are bacillus bacteria easily cultured in labs?
Yes
What is bacillus cereus, and what disease is it commonly associated with?
A opportunistic pathogen associated with exogenous endophthalmitis
What is the gram stain, shape, and metabolic type of clostridia? Do they produce spores?
Large gram positive rods
Produce spores
Obligate anaerobes
Where are clostridia found (3)?
Soil, dust, and the GIT of warm-blooded animals (including humans)
What two diseases can clostridia cause?
Keratitis and exogenous endophthalmitis
Name three species of clostridia, and a disease associated with each.
C. tetani - tetanus
C. botulinum - botulism
C. perfringens - gas gangrene/food poisoning
Describe the gram stain ,shape, and metabolic type of enterobacteriaceae.
Gram negative rods
Facultative anaerobes
Name 4 enterobacteriaceae associated with ocular disease. Describe which are normal microbiota, and which arent.
Environmental (associated with water)
-Serratia
Normal microbiota
-Proteus
-E. coli
-Klebsiella
In what two ways are enterobacteriaceae associated with ocular disease?
Contact lens associated infections
Penetrating eye injuries
Are enterobacteriaceae resistant or susceptible to antimicrobials?
Can be very resistant
How can enterobacteriaceae infections be managed (1) and prevented (1)?
Due to resistance, antibiotic susceptibity testing is essential
Prevention of CL infections by improving wearing and cleaning compliance
What kind of stain, metabolic type, and shape are mycobacteria?
Acid fast stain needed
Large rods
Aerobic
Name the two major mycobacteria, and the disease they cause.
M. tuberculosis - tuberculosis
M. leprae - leprosy
Do mycobacteria grow fast or slowly? Describe why.
Slow growing due to restricted entry of nutrients through its waxy cell wall
Do tuberculosis or leprosy infect the eye as part of a systemic infection?
Yes
Name two mycobacteria species that cause keratitis? What other disease can they cause?
M. chelonae
M. fortuitum
They can also cause endophthalmitis
What disease can mycobacteria rarely cause?
Scleritis
Name two means of managing mycobacteria infection.
Susceptibility testing for antibiotics
Surgery for patients who dont respond
What kind of sterol can be found in the cell membrane of fungi?
Ergosterol
In what two ways do fungi propagate?
Vegetatively or by spores
What are the two classifications of fungi (3)?
Yeast - unicellular
Moulds - filamentous
Some can be both - dimorphic
Define saprophytic.
Gain energy from the breakdown of dead organic matter
Can fungi infect eyes with an intact epithelium?
Rarely - they are opportunistic
Are fungal eye infections common? What is the most common disease?
They are rare.
Keratitis is the most common
How do fungi cause corneal damage?
Injury by tree branches
What fungal infection do CL wear predispose one to?
Oculomycoses
What fungi is involved with causing fungal endophthalmitis in hospitalised patients?
Candida sp.
Name 4 common fungi for ocular infections and their classification.
Yeast
-Candida (especially albicans)
Filamentous
-Fusarium
-Aspergillus
-Scedosporium
Name 4 means of pathogenesis for fungal infectious agents.
Adhesins
Pseudohyphae in some species
Fungal toxins
Inducing inflammation
Can candida albicans be found in healthy individuals?
Yes, in 50% of healthy people it is found on most mucous membranes
What is the ideal specimen for a suspected fungal infection?
Discharge swab, corneal scrapings
What can be expected in a microscope image of a suspected fungal infection (4)?
Direct examination of pus, corneal scrapings may show yeast/hyphae/spores.
On what media do fungi grow, yeast and others?
HBA for yeasts or SAB for others.
What is the management for a fungal infection? Name a problem with treating fungal infections.
Long term antifungal chemotherapy.
Difficult to achieve selective toxicity.
What do antifungals often target?
The cell membrane of fungi.
