Microbiology Flashcards
What is infection of the cornea known as?
Keratitis
What is infection of the entire globe of the eye known as?
Endophthalmitis
What organisms commonly cause bacterial conjunctivitis in neonates?
Staph aureus, Neisseria gonorrhoeae, chlamydia trachomatis (all need referral to ophthalmology)
What are some causes of bacterial conjunctivitis in other age groups?
Staph aureus, strep pneumoniae, haemophilus influenzae (especially in children)
What is the treatment for bacterial conjunctivitis?
Swab then topical antibiotic = usually chloramphenicol qds
When should chloramphenicol be avoided?
If history of aplastic anaemia or allergic reaction to drug
What are some causes of viral conjunctivitis?
Adenovirus, herpes simplex, herpes zoster
When should chlamydial conjunctivitis be suspected?
Chronic history = unresponsive to treatment
Bilateral conjunctivitis in young patient
What symptoms may also be present in chlamydial conjunctivitis?
Those of urethritis or vaginitis
What must be done if chlamydial conjunctivitis is diagnosed?
Contact tracing must be done for that patient
What is a potential complication of chlamydial conjunctivitis?
Subtarsal scarring
What organisms may cause the formation of hypopyon in keratitis?
Bacterial or fungi
What is hypopyon?
White exudate in anterior chamber with underlying redness of the conjunctiva and underlying episclera
What is bacterial keratitis usually associated with?
Other corneal pathology or contact lens wear
How are patients with bacterial keratitis managed?
Admitted to hospital and given hourly drops, reviewed daily
What are the main viral causes of keratitis?
Herpes and adenovirus
What are the features of herpetic keratitis?
May have dendritic ulcer, very painful, can be recurrent
What do recurrences of herpetic keratitis result in?
Reduced corneal sensation
What may occur if herpetic keratitis is treated with steroids?
May cause corneal melt or perforation
What are some features of adenovirus keratitis?
Show subepithelial infiltrates, bilateral, usually follows URTI, may affect vision
When are steroids used on adenovirus keratitis?
To speed up recovery if chronic
When are topical antibiotics used in adenovirus keratitis?
To prevent secondary infection
What fungal organisms that cause keratitis are associated with contact lenses?
Acanthamoeba, pseudomonas aeruginosa
What are the features of fungal keratitis?
More indolent course than microbial keratitis, usually history of trauma from vegetation, takes long time to heal
What are the symptoms of orbital cellulitis?
Painful (especially on eye movement), proptosis, often associated with paranasal sinusitis, pyrexia
Is orbital cellulitis serious?
Yes = sight threatening, patient needs care from ENT and ophthalmology
Why are CT scans done in orbital cellulitis?
To identify orbital abscesses
What are some sources of orbital cellulitis?
Direct extension from sinus, extension from focal orbital infection (e.g infected chalazion, dacryocystitis), may be post-operative
What must you differentiate between in orbital cellulitis?
Preseptal or orbital infection
What organisms are associated with orbital cellulitis?
Staph, strep, coliforms, haemophilus influenzae, anaerobes
When should you do a scan on a patient with orbital cellulitis?
If there is a suggestion of restrictions of muscles or optic nerve dysfunction
How is orbital cellulitis treated?
Broad spectrum antibiotic and monitor closely, sometimes abscesses need drained
What is endophthalmitis?
Devastating infection of inside of eye = may be post-surgical or endogenous, sight threatening
What are some symptoms of endophthalmitis?
Very painful, decreased vision, very red eye
What organisms cause endophthalmitis?
Often conjunctival commensals = usually staph epidermidis
What is the treatment for endophthalmitis?
Intravitreal amikacin/ceftazidime/vancomycin and topical antibiotics
What are some common causes of chorioretinitis?
CMV in AIDS patients, toxoplasma gondii, toxocara canis
What is a feature of chorioretinitis caused by CMV in AIDS patients?
Usually haemorrhagic
What is toxoplasma gondii?
Protozoan infection = usually from cats or raw meat, usually causes mild flu like illness that causes no further problems
How does toxoplasma gondii act in immunocompetent patients?
Enters latent phase with cyst forming
Can reactivate and needs systemic treatment if sight threatening
What is toxocara canis?
Parasitic nematode (roundworm) that normally affects cats and dogs
Why is toxocara canis infection self-limiting?
Organism unable to replicate in humans = remains in immature form (larvae)
How may toxocara infection affect sight?
Can form granulomas which may threaten sight
What organisms is swabbing for culture suitable for?
Bacterial, viral, chlamydial
How is bacterial keratitis diagnosed?
Corneal scrapes
How is endophthalmitis diagnosed?
Aqueous/vitreous sample for culture
How is acanthamoeba diagnosed?
Microscopy and culture
How are toxoplasma and toxocara diagnosed?
Serology
What is chloramphenicol?
Most commonly used topical antibiotic = ointment or drops
How does chloramphenicol work?
Inhibits peptidyl transferase = stops bacterial protein being made
What are some organisms that chloramphenicol is active against?
Bactericidal = strep, haemophilus influenzae Bacteriostatic = staph
What are some side effects of chloramphenicol?
Allergy, irreversible aplastic anaemia, grey baby syndrome
What are some antibiotics that inhibit bacterial cell wall synthesis?
Penicillin and cephalosporins = have common beta lactam ring
What does a beta lactam ring do to bacteria?
Inhibits the enzyme that makes the bacterial cell wall
What is an antibiotic class that inhibits nucleic acid synthesis?
Quinolones = inhibit DNA gyrase (enzyme that compresses bacterial DNA into supercoils), inhibition of DNA gyrase leads to unwinding of supercoils
What is a common contaminate of eye drop bottles?
Pseudomonas = bottles must be kept contaminate free for four weeks (get new drops after 28 days)
What are some antibiotics used to treat bacterial conjunctivitis?
Chloramphenicol = treats most (except p.aeruginosa)
Fusdic acid = treats staph aureus
Gentamicin = treats most gram negatives
How does aciclovir work?
Inhibits viral DNA synthesis
What are some features of aciclovir?
Base analogue (mimics guanine), topical and systemic, used for dendritic ulcers of cornea
How is chlamydial conjunctivitis treated?
Topical oxytetracycline = adults may also need azithromycin for genital chlamydial infection
What are some antibiotics used to treat bacterial keratitis?
4-quinolone (ofloxacin) = treats most gram negative but not active against strep. pneumoniae
Gentamicin + cefuroxime = combo will treat most gram negatives and positive organisms
What is the distinguishing feature of chlamydial conjunctivitis?
It causes follicles
