Flashcards in Microbiology Deck (42):
What is the most common cause of viral conjunctivitis?
Adenovirus (post-natal), HSV (neonatal)
What other things can cause viral conjunctivitis?
Coxsackie A24, HSV 1 and 2, VZV, EBV, rubella, mumps, influenza
What clinical findings are associated with viral conjunctivitis?
Recent URI, preauricular adenopathy
How to treat viral conjunctivitis?
Benign and self limited - treat with cold compress and topical vasoconstrictors
What are the most common causes of acute bacterial conjunctivitis in kids?
Staphylococcus aureus, Strep. pneumoniae, Haemophilus influenzae (Moraxella lacunata)
What is the most common cause of acute bacterial conjunctivitis in adults?
How to treat bacterial conjunctivitis?
Trimethoprim & polymyxin ophthalmic drops (Polytrim)
-Can also use expensive moxifloxacin (fluoroquinolone) drops
How does Moxifloxacin work?
Bactericidal - Inhibits DNA replication by binding bacterial topoisomerase II and IV
How does polymyxin B work?
Binds LPS in membrane creating holes leading to the release of cellular contents
-Helps facilitate the entry of other antibiotics
-Can be used for gram -, multi drug resistant organisms
What is the mechanism of trimethoprim?
Bacteriostatic - Inhibits bacterial dihydrofolate reductase, has low affinity for mammalian enzyme (similar to MTX!)
What is bacterial conjunctivitis caused by neisseria like?
-Copious yellow-green discharge (purulent)
-Gram -, intracellular, diplococci, growth on chocolate agar
How to treat neisseria gonorrhoeae eye infections??
What is ophthalmia neonatorum and how do we prevent it?
Conjunctivitis or keratoconjunctivitis occurring within the first four weeks of birth
-Prophylaxis with Erythromycin!
What is the mechanism of erythromycin?
It inhibits translation by binding 23S rRNA of the 50S subunit
Spectrum: mostly chlamydia
What are the two types of chlamydia trachomatis?
-Inclusion conjunctivitis (serotypes D-K)
-Trachoma (serotypes A-C) leading cause of blindness worldwide due to multiple infections since no long lasting immunity
How to diagnose and treat chylamydia trachomatis?
Diagnosis: direct fluorescent antibody
Treat: azithromycin & improve hygiene (treat partners!)
What do you see on pathology of chlamydia trachomatis?
Blue/Purple basophilic inclusion bodies
How does chlamydia trachomatis infect cells?
Elementary body (EB) enters epithelial cells, converts to reticulate body (RB), and then replicates using binary fission
What does HSV-1 keratoconjunctivitis look like?
You can see the green lines in eye on blue light exam.
-Similar presentation to adenovirus although lesions can be painful especially if scarring of the cornea occurs and often only in one eye
How to treat HSV-1 keratoconjunctivitis?
Corneal involvement - use tropical trifluridine
& systemic acyclovir
How does trifluridine work against HSV-1?
Similar to acyclovir, it is a pyrimidine analog (pretends to be DNA) that disrupts DNA/RNA production. It is effective against acyclovir resistant virus bc it can be phosphorylated by host kinases also making it much more toxic.
(ONLY USE TOPICALLY)
How to treat bacterial keratitis?
Moxifloxacin eye drops!
Properties of pseudomonas aeroginosa?
-Gram -, aerobic rod, flagella
-Naturally resistant to many antibiotics and disinfectants due to ability to form biofilms
What can cause chorioretinitis and what does it show on fundoscopic exam?
Congential toxoplasma & CMV - HIV & neonates
Fundoscopic exam: it begins at periphery and spreads like "brushfire"
What should you use to treat toxoplasmosis?
Folate antagonist - like Sulfadiazine or Pyrimethamine
What is chronic conjunctivitis often associated with?
Chlamydia trachomatis and herpes
What is acute otitis media?
Bacterial or viral
-Pain, red ear drum, pus and fever
What is otitis media with effusion?
Build up of fluid in eustachian tube
-No infection, associated with URI, cigarette smoke, allergies
-Resolves on its own
What causes acute otitis media?
1. URI or allergic conditions cause congestion of mucosa
2. Narrowing or obstruction of eustachian tube prevents ventilation and drainage. Anatomic abnormalities or enlarged adenoids increases likelihood of blockage
3. Accumulation of secretions of middle ear and if pathogen is present AOM
What are the most common causes of Acute Otitis Media?
1. Streptococcus pneumoniae
2. Haemophilus influenzae
3. Moraxella catarrhalis
4. Viral (RSV, rhinovirus)
Properties of streptococcus pneumoniae?
Gram +, diplococcus, unique capsules
-Asymptomatic colonization of naso-oropharynx can be a carrier for weeks to months especially in winter
What are the virulence factors of streptococcus pneumoniae?
-Resistance - changes in penicillin binding protein
-Capsule - blocks phagocytosis by interfering with the deposition of complement on surface of organism
-Choline-binding proteins - bind carbohydrates present on surface of epithelial cells
-Pneumolysin - pore forming toxin released that disrupts ciliary beating
Traits of Haemophilus influenzae?
Gram -, coccobacillus, nonmotile, biofilms, facultative anaerobe
-Needs Hematin (X) and NAD (V) in chocolate agar for growth
-Many express Beta-lactamases
Properties of Moraxella catarrhalis?
Gram -, aerobic, diplococcus, oxidase-positive, nonmotile, fastidious-chocolate agar, pili
-Colonizes upper resp. tract in infants
-Most produce beta-lactamases
-Hockey puck test - easily slide across agar
What is the recommended treatment for acute otitis media in adults (over 24 months)?
Ibuprofen & decongestants
How to treat acute otitis media for 6-24 month old?
-Empiric treatment = Amoxicillin (covers strep. pneumoniae, H. influenzae)
-If doesn't improve in 48 hours, switch to amoxicillin-clavulanate (bacteria may have beta-lactamase) - if pregnant, no clavulanate
How to treat acute otitis media in baby with penicillin allergy?
What are some complications of otitis media?
-Conductive hearing loss/delayed speech due to perforation of tympanic membrane & erosion of ossicles
-Cholesteatoma -cyst of epithelial cells
-Infection spreads to mastoid, inner ear, temporal bone, meninges, brain
What is otitis externa?
-Inflammation of ear canal, itching, purulent ear drainage
-Risk factors: trauma, foreign bodies, excessive moisture, diabetes
What are the common etiologies for otitis externa?
-Acute localized - most often staphylococcus pustule or furuncle associated with hair follicles
-Acute diffuse - pseudomonas aeruginosa - itches, red canal, and painful
-Malignant - pseudomonas aeruginosa - invasion of adjacent bone and cartilage which can progress to cranial nerve palsy and death - more common with elderly, poorly controlled diabetes, immunocomprimsed
-Fungal - Aspergillus & Candida albicans
How to treat otitis externa?
-Avoid flushing unless TM is intact
-Treat with analgesics
-Topical antibiotics = neomycin + polymyxin + hydrocortisone