Microbiology Flashcards
Does gram + bacteria have a cell wall? What colour will it stain? What two subtypes does it have?
Yes it has a cell wall It will stain purple Can be cocci or bacilli
Gram + cocci can be what?
Staph or strep
Does gram - bacteria have a cell wall? What colour will it stain? What three subtypes does it have?
No it doesn’t have a cell wall It will stain pink Can be cocci, cocci-bacilli or bacilli
What is Neisseria an example of?
Gram - cocci
What is an example of a gram - cocci-bacilli?
Haemophilus influenzae
What is an example of a gram - bacilli?
Pseudomonas
How can you tell apart bacterial and viral conjunctivitis by clinical presentation?
Bacterial- pus Viral- extremely watery
Bacterial conjunctivitis can be an indicator of what?
A more severe infection in neonates (always refer to ophthalmology)
Who is bacterial conjunctivitis most common in?
Neonates
What organisms can cause bacterial conjunctivitis in neonates?
- Neisseria Gonorrhoeae - Staph Aureus - Chlamydia Trachomatis
What organisms can cause bacterial conjunctivitis in non-neonates?
- Staph Aureus - Haemophilus Influenzae - Strep Pneumoniae
Haemophilis influenzae infection is most common in who?
Children
What is the antibiotic of choice for bacterial conjunctivitis? How can this be taken? How often is it taken?
- Chloramphenicol - Topically or as drops - 4 times daily
When should chloramphenicol not be given?
If there is any history of aplastic anaemia or allergy
If symptoms of bacterial conjunctivitis worsen after treatment, what could this be suggestive of?
Drug allergy
What bacteria does chloramphenicol not treat? If for any reason chloramphenicol cannot be used, what are some other treatment options?
It does not treat pseudomonas aeruginosa. Other options are fusidic acid (staph aureus) or gentamicin (gram -‘s)
What is most likely the cause if bacterial conjunctivitis presents with a chronic history and is unresponsive to treatment with chloramphenicol?
Chlamydial conjunctivitis
When should chlamydial conjunctivitis be suspected?
When there is bilateral conjunctivitis in a young adult (who may or may not have symptoms of urethritis/vaginitis)
Chlamydial conjunctivitis requires contact tracing. It also causes scarring where?
Underside of the eyelid
How do you treat chlamydial conjunctivitis?
Topical oxytetracycline (adults may also need oral azithromycin for genital chlamydia)
What are 3 organisms causing viral conjunctivitis?
- Adenovirus - Herpes Simplex - Herpes Zoster
What is the general treatment for viral conjunctivitis?
Usually self-limiting, use a cold press. Can occasionally give antibiotics to prevent a secondary infection.
What is Hutchinson’s sign? What does it precede?
Vesicles on the tip or side of the nose, suggestive of damage to the nasociliary branch of the trigeminal nerve. It precedes Herpes Zoster.
How should Herpes Zoster be treated?
Aciclovir (ideally in 72 hours)
What is keratitis?
Inflammation of the cornea
Keratitis presents with a very short history and acute onset vision disturbance. What is the most likely cause?
Bacterial
Bacterial keratitis often occurs with hypopyon. What is this?
Inflammatory cells in the anterior chamber of the eye which causes a characteristic white clouding
Who does bacterial keratitis tend to occur in?
Those with other corneal pathology or wear contact lenses
Why do patients with bacterial keratitis need hospital admission?
Hourly eyedrops and a daily review- this can be sight threatening
What is the main treatment for bacterial keratitis? What organism does this NOT target?
Oflaxacin- not active against strep pneumoniae
What combination treatment can be used in bacterial keratitis?
Gentamycin and cefuroxime
Keratitis associated with contact lenses is most often caused by what organism?
Pseudomonas aeruginosa
What are the 2 causes of viral keratitis?
Adenovirus and herpes
What condition cannot be treated with steroids? Why?
Herpetic keratitis- can cause a corneal melt and perforation
How does adenoviral keratitis usually present?
Bilaterally after an URTI
Is adenoviral keratitis infectious? How is it treated?
Yes it is infectious. You can give topical antibiotics to prevent secondary infections or steroids to speed up recovery.
Keratitis presents with a long history of slow onset with an eye which is not as red as would be expected and is not particularly sore. What is the most likely cause?
Fungi from a history of trauma from vegetation
What is orbital cellulitis often preceded by?
Paranasal sinusitis, or an operation (common post-operative complication)
What are some complications of orbital cellulitis?
- Compartment syndrome - Compromised optic nerve - Infection passing to the cranial fossa - Compromised medial rectus muscle
What are some organisms which can cause orbital cellulitis?
Staph, strep, coliforms, HI, anaerobes
What test is used to detect orbital abscesses? When else are these used?
CT scans, also used if there are suggestions of muscle restriction or optic nerve dysfunction
What is endopthalmitis? What can cause it?
Devastating infection causing inflammation of the entire eye- can be caused post-surgery or by a dormant organism
What is the most common organism causing endopthalmitis?
Staph epidermidis
How is endopthalmitis treated?
Intra-vitreous amikacin/caftazidime/vancomycin and topical antibiotics
What is chorioretinitis?
Infection at the back of the eye
CMV in AIDS, toxoplasma gondii and toxocara canis are causes of what?
Chorioretinitis
Where does toxoplasma gondii come from? What type of organism is it?What happens if it is present in immunocompromised? When does it require treatment?
Cats and raw meat- it is a protozoa. In immunocompromised it forms cysts and can reactivate. It only requires treatment if sight threatening.
What is toxocara canis? What happens when it is in humans?
A parasitic nematode. In humans it forms granulomas though is unable to replicate.
What is the diagnostic test for conjunctivitis?
Swabs
What is the test for bacterial keratitis?
Corneal scrapes
What is the best test for endophthalmitis?
Aqueous/vitreous humour culture
What is the best test for toxoplasma and toxocara?
Serology
What are the 3 broad categories of antibiotic and give examples?
- Inhibit protein synthesis (chloramphenicol) - Inhibit cell wall synthesis (penicillins and cephalosporins) - Inhibit nucleic acid synthesis (quinolones)
How does chloramphenicol work? It is bactericidal for what? It is bacteriostatic for what?
Inhibits the peptide transferase enzyme to stop bacterial protein being made. Bactericidal for strep and haemophilus and bacteriostatic for staph.
What are the side effects of chloramphenicol?
- Allergy - Irreversible aplastic anaemia - Grey baby syndrome
What organism is a common contaminant of old eyedrop bottles?
Pseudomonas
What % acyclovir should be used in the eye?
3%
What is this?
Bacterial conjunctivitis
What is this?
Adenoviral conjunctivitis
What is this?
Herpes Simplex conjunctivitis
What is this?
Herpes Zoster conjunctivitis
What condition causes this scarring?
Chlamydial conjunctivitis
What is this?
Bacterial keratitis with hypopyon
What is this?
Dendritic ulcer from herpetic keratitis
What is this?
Orbital cellulitis
What is this?
Endophthalmitis
What antibiotics should be given for orbital cellulitis?
IV ceftriaxone, flucloxacillin and metronidazole
What complication should you be most worried about with regards to orbital cellulitis?
Cavernous sinus thrombosis
