Microbiology

Question 1

What is the most common cause of viral conjunctivitis?

Answer 1

Adenovirus (post-natal), HSV (neonatal)

Question 2

What other things can cause viral conjunctivitis?

Answer 2

Coxsackie A24, HSV 1 and 2, VZV, EBV, rubella, mumps, influenza

Question 3

What clinical findings are associated with viral conjunctivitis?

Answer 3

Recent URI, preauricular adenopathy

Question 4

How to treat viral conjunctivitis?

Answer 4

Benign and self limited - treat with cold compress and topical vasoconstrictors

Question 5

What are the most common causes of acute bacterial conjunctivitis in kids?

Answer 5

Staphylococcus aureus, Strep. pneumoniae, Haemophilus influenzae (Moraxella lacunata)

Question 6

What is the most common cause of acute bacterial conjunctivitis in adults?

Answer 6

Staphylococcus aureus

Question 7

How to treat bacterial conjunctivitis?

Answer 7

Trimethoprim & polymyxin ophthalmic drops (Polytrim)

-Can also use expensive moxifloxacin (fluoroquinolone) drops

Question 8

How does Moxifloxacin work?

Answer 8

Bactericidal - Inhibits DNA replication by binding bacterial topoisomerase II and IV

Question 9

How does polymyxin B work?

Answer 9

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

Question 10

What is the mechanism of trimethoprim?

Answer 10

Bacteriostatic - Inhibits bacterial dihydrofolate reductase, has low affinity for mammalian enzyme (similar to MTX!)

Question 11

What is bacterial conjunctivitis caused by neisseria like?

Answer 11

Neisseria gonorrhoeae

• Copious yellow-green discharge (purulent)
• Preauricular adenopathy
• Gram -, intracellular, diplococci, growth on chocolate agar

Question 12

How to treat neisseria gonorrhoeae eye infections??

Answer 12

Systemic ceftriaxone!

Question 13

What is ophthalmia neonatorum and how do we prevent it?

Answer 13

Conjunctivitis or keratoconjunctivitis occurring within the first four weeks of birth
-Prophylaxis with Erythromycin!

Question 14

What is the mechanism of erythromycin?

Answer 14

It inhibits translation by binding 23S rRNA of the 50S subunit
Spectrum: mostly chlamydia

Question 15

What are the two types of chlamydia trachomatis?

Answer 15

• Inclusion conjunctivitis (serotypes D-K)
• Trachoma (serotypes A-C) leading cause of blindness worldwide due to multiple infections since no long lasting immunity

Question 16

How to diagnose and treat chylamydia trachomatis?

Answer 16

Diagnosis: direct fluorescent antibody
Treat: azithromycin & improve hygiene (treat partners!)

Question 17

What do you see on pathology of chlamydia trachomatis?

Answer 17

Blue/Purple basophilic inclusion bodies

Question 18

How does chlamydia trachomatis infect cells?

Answer 18

Elementary body (EB) enters epithelial cells, converts to reticulate body (RB), and then replicates using binary fission

Question 19

What does HSV-1 keratoconjunctivitis look like?

Answer 19

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

Question 20

How to treat HSV-1 keratoconjunctivitis?

Answer 20

Corneal involvement - use tropical trifluridine

& systemic acyclovir

Question 21

How does trifluridine work against HSV-1?

Answer 21

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)

Question 22

How to treat bacterial keratitis?

Answer 22

Moxifloxacin eye drops!

Question 23

Properties of pseudomonas aeroginosa?

Answer 23

• Gram -, aerobic rod, flagella
• Opportunistic infection
• Naturally resistant to many antibiotics and disinfectants due to ability to form biofilms

Question 24

What can cause chorioretinitis and what does it show on fundoscopic exam?

Answer 24

Congential toxoplasma & CMV - HIV & neonates

Fundoscopic exam: it begins at periphery and spreads like “brushfire”

Question 25

What should you use to treat toxoplasmosis?

Answer 25

Folate antagonist - like Sulfadiazine or Pyrimethamine

Question 26

What is chronic conjunctivitis often associated with?

Answer 26

Chlamydia trachomatis and herpes

Question 27

What is acute otitis media?

Answer 27

Bacterial or viral | -Pain, red ear drum, pus and fever

Question 28

What is otitis media with effusion?

Answer 28

Build up of fluid in eustachian tube - No infection, associated with URI, cigarette smoke, allergies - Resolves on its own

Question 29

What causes acute otitis media?

Answer 29

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

Question 30

What are the most common causes of Acute Otitis Media?

Answer 30

1. Streptococcus pneumoniae 2. Haemophilus influenzae 3. Moraxella catarrhalis 4. Viral (RSV, rhinovirus)

Question 31

Properties of streptococcus pneumoniae?

Answer 31

Gram +, diplococcus, unique capsules - chronic diseases - Asymptomatic colonization of naso-oropharynx can be a carrier for weeks to months especially in winter

Question 32

What are the virulence factors of streptococcus pneumoniae?

Answer 32

- 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 - Neuraminidases - Pneumolysin - pore forming toxin released that disrupts ciliary beating

Question 33

Traits of Haemophilus influenzae?

Answer 33

Gram -, coccobacillus, nonmotile, biofilms, facultative anaerobe - Needs Hematin (X) and NAD (V) in chocolate agar for growth - Many express Beta-lactamases

Question 34

Properties of Moraxella catarrhalis?

Answer 34

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

Question 35

What is the recommended treatment for acute otitis media in adults (over 24 months)?

Answer 35

Ibuprofen & decongestants

Question 36

How to treat acute otitis media for 6-24 month old?

Answer 36

- 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

Question 37

How to treat acute otitis media in baby with penicillin allergy?

Answer 37

Azithromycin

Question 38

What are some complications of otitis media?

Answer 38

- 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

Question 39

What is otitis externa?

Answer 39

Swimmer's ear - Inflammation of ear canal, itching, purulent ear drainage - Risk factors: trauma, foreign bodies, excessive moisture, diabetes

Question 40

What are the common etiologies for otitis externa?

Answer 40

- 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

Question 41

How to treat otitis externa?

Answer 41

- Avoid flushing unless TM is intact - Treat with analgesics - Topical antibiotics = neomycin + polymyxin + hydrocortisone

Question 42

What do you see in pathology of herpes zoster?

Answer 42

Multi-nucleated giant cells!