Virology and Mycology (2)

Question 1

Explain opportunistic mycoses
What species are common causes? (3)

Answer 1

Caused by endogenous or ubiquitous organisms of LOW virulence that cause infection in immunocompromised patients

Species
- Candida
- Cryptococcus
- Aspergillus

Question 2

Can candida be part of normal flora?

Answer 2

Yes

Question 3

Candida can produce pseudohyphae and hypae. Define pseudohyphae

Answer 3

Pseudohyphae:
Form when buds continue to grow but fail to detach

Question 4

What group of patients are cutaneous candidiasis common in?
location

Answer 4

Who: obese, diabetic
Location: skin fold, groin, axillae

Question 5

What group of patients are candidal onychomycosis common in?
location?

Answer 5

Who: chronic CUTANEOUS candidiasis
Location: nails

Question 6

Which candida causes bloodstream infections, wound infections, or ear infections and are often multidrug-resistant

Answer 6

Candida Auris

Question 7

How to diagnose candidiasis (3)

Answer 7

microscope: KOH mount of skin/nails scrapings
- will show psuedohyphae/true hyphae

Culture at 37C

Tissue biopses, gram-staining

Question 8

Explain what gram-positive and gram-negative stains of fungi look like?

Answer 8

Gram-positive
- Intact YEAST cells

Gram-negative
- broken/disrupted cells during the dye process

Question 9

How do Fungi stain gram-positive if they don’t have peptidoglycan?

Answer 9

Other structures can retain the stain such as:
- chitin
- beta-glucan
- Mannoprotein

Question 10

Cryptococcosis
Causative fungi
Location?
What group of patients?
Type of capsule?
Found in?

Answer 10

Causative fungi
- Cryptococcus neoformans

Location?
- Lungs, meninges

What group of patients?
- AIDS patients

Type of capsule?
- polysaccharide capsule

Found in?
- vegetation, soil
- pigeon feces

Question 11

What is the lab diagnosis of cryptococcosis? (3)

Answer 11

1. Specimens: blood, urine
2. Microscopic examination
   - wet mounts using INDIA INK (capsule stays white (bright))
3. Culture at 37C

NOT SEROLOGY

Question 12

Aspergillosis
Pathogens (2)
Produce (morphology)

Answer 12

Pathogens
- aspergillus fumigatus
- Aspergillus flavus

Produce
- small conidia that is easily aerosolized
- rapidly produce aerial hyphae that have long conidiophores with terminal vesicles

Question 13

Define the following forms of aspergillosis:
Allergic bronchopulmonary aspergillosis
Aspergilloma
Invasive pulmonary aspergillosis

Answer 13

Allergic bronchopulmonary aspergillosis
- diagnosed by high titres of IgE antibody to aspergillus

Aspergilloma
- spherical growth of aspergillys in pre-existing lung cavities

Invasive pulmonary aspergillosis
- disease start in lungs and move to other organs
- produces abscesses and necrotic (cell death) lesions

Question 14

Lab diagnosis of Aspergillosis? (4)

Answer 14

1. Specimens
2. Microscopic examination w KOH or calcofluor
   - branched septate hyphae
3. Culture at room temperature
4. Serology (IgE)

Question 15

Pneumocystis pneumo
Pathogen
Spread?
Morphology?
Who is at risk?
Location?

Answer 15

Pathogen
- pneumocystis jiroveci

Spread?
- by inhalation

Morphology?
- thin-walled trophozoites + thick cysts

Who is at risk?
- AIDS, immunocompromised, malnourished

Location?
- Lungs, human
- cannot culture ex-vivo

Question 16

Lab diagnosis of pneumocystis (4)

Answer 16

1. Specimens
2. Microscopic examination
   - look for cysts or trophozoites
3. Serology
4. PCR

Question 17

What are 2 treatment options for pneumocystis penumonia

Answer 17

Trimethoprim
Sulfamethoxazole

Question 18

Differentiate between fungicidal and fungistatic

Answer 18

fungicidal: kills fungi
fungistatic: inhibits growth

Question 19

Antifungals: Polyenes
Examples (2)
Indication
MOA
Fungicidal/fungistatic/both

Answer 19

Examples (2)
- Amphotericin B, Nystatin

Indication
- Used for systemic mycoses eg. coccidioiomycosis (valley fever)

MOA
- polyenes form complexes with ergosterol –> membrane damage/leakage –> cell death

Fungicidal

Question 20

Antifungals: Nucleic acid inhibitor
Example
Indication
MOA
Fungicidal/fungistatic/both

Answer 20

Example
- Flucytosine

Indication
- cryptococcal/meningitis (an endemic mycoses)

MOA
- Drug enters fungal cells (using cytosine permease) –> converted to 5-fluorocytosine –> competes with uracil (inhibits RNA/protein synthesis)

Fungicidal OR fungistatic

Question 21

Azoles
Imidiazole examples
Triazole examples
MOA
Fungicidal/fungistatic/both
Indication (3)

Answer 21

Imidiazole examples
- clotrimazole, ketoconazole

Triazole examples
- fluconazole, voriconazole, itraconazole

MOA
- azole interfere with synthesis of ergosterol (cell wall)
- Fungistatic

Indication
- Vaginal yeast infection
- Oral thrush
- Tinea versicolour

Question 22

Allylamines
Example
MOA
Fungicidal/fungistatic/both
Indication

Answer 22

Example
- Terbinafine (lamisil)

MOA
- blocks ergosterol synthesis by inhibiting squalene epoxidase

Fungicidal/fungistatic/both
- Can be both

Indication
- Dermatophyte infection - FUNGICIDAL eg. athletes foot, jock itch
- Candida albicans - FUNGISTATIC eg. oral thrush, yeast infection

Question 23

Echinocandins
Example
MOA
Fungicidal/fungistatic/both
Indication

Answer 23

Example
- Capsofungin

MOA
- inhibits 1,3B-glucan synthase –> disrupt polysaccharide B-glucan –> disrupt cell wall integrity

Fungicidal/fungistatic/both
- can be both

Indication
- Invasive aspergillosis - FUNGISTATIC
- systemic candidiasis - FUNGICIDAL

Question 24

Which 2 antifungals can be given IV?

Answer 24

• Polyenes
• Echinocandins

Question 25

Which 2 antifungals when given together works well against coccidioidomycosis and other endemic mycoses

Answer 25

Polyenes + nucleic acid inhibitors Amphotericin B + Flucytosine

Question 26

Mitotic microtubules inhibitor Example MOA Fungicidal/fungistatic/both Indication

Answer 26

Example - griseofulvin MOA - concentrates in the stratum corneum --> inhibits hyphal growth - ORAL not topical fungiSTATIC Indication - treatment of dermatophytosis (fungiSTATIC) eg. tinea pedis, urnguium etc...