MICRO: Fungal Infections

Question 1

what is fungus?

Answer 1

• eukaryotes and obligate aerobes (must have oxygen)
• sexual or asexual reproduction
• found everywhere in environment (ubiquitous)
• most aren’t pathogenic e.g. beer
• have B-glucans and chitin in cell wall, ergosterol in cell membrane
• can exist as yeasts, moulds or both (dimorphic)

Question 2

fungus shapes

Answer 2

• mycelium (mould): thick mat of hyphae (branches - septate or non-septate) - looks furry, grow by extending hyphae and then ‘fruiting bodies’ on end release spores
• yeasts: spherical cells that bud off, forming daughter cells
• pseudomycelium: chains of yeast cells

Question 3

examples of yeasts (budding daughter cells)

Answer 3

• candida, cryptococcus, pneumocystis

Question 4

example of mould (hyphae mats)

Answer 4

• aspergillus

Question 5

dimorphic fungi (both yeast and mould)

Answer 5

• mould @ 25˚C
• yeast @ 37˚C
  e.g. sporothrix
  (candida is opposite)

Question 6

aspergillus toxins

Answer 6

• release toxin called aflatoxin
• hepatotoxic and carcinogenic
• plant crops e.g. nuts, corn or eating contaminated meat

Question 7

cutaneous/superficial mycosis: examples, transmission, Dx

Answer 7

• caused by dermatophytes
• only affect hair, skin, nails b/c of keratin
• ringworm (fungus)/tinea
• human-human transmission, soil, zoonosis
• like warm, moist environments
• Dx: skin/nail clippings > break down skin w/ KOH and stain remaining fungus

Question 8

subcutaneous mycosis

Answer 8

• usually following inoculation e.g. rose thorn > Rose Gardener’s disease (sporotrichosis - sporothrix)
• can be a single lesion or travel through proximal lymphatics and create multiple lesions
• long treatment b/c slow growth

Question 9

cryptococcus

Answer 9

• C. neoformans: infects immunosuppressed ppl
• C. gattii: infects healthy ppl
• mostly from dry pigeon droppings
• causes meningitis + lung infections
• no person-person spread
• high mortality

Question 10

pneumocystis: who does it affect, mortality, transmission, Sx, Dx

Answer 10

• ubiquitous in environment
• infects HIV/AIDS and immunocompromised
• low mortality
• transmission: person-person thru air
• Sx: SOB, dry cough, LOW, fever
• Dx: PCR, B-D glucan test

Question 11

aspergillus

Answer 11

• mould found in rotting vegetation
• not part of normal flora
• transmission: inhalation of spores
• causes allergic bronchopulmonary aspergillosis
• A. fumigatus, A. niger, A. flavus
• high mortality

Question 12

candida: Sx, Dx, mortality, who is at risk

Answer 12

• can be normal flora
• Sx: fever and chills that X improve after antibiotics for suspected bacterial infection, oral/vaginal thrush (thick biofilm ECM)
• invasive when enters blood (candidaemia) and easily disseminates esp to eyes - very high mortality
• IV drug users @ risk
• Dx using PCR

Question 13

what is maldi tof + advantages and disadvantages

Answer 13

• uses mass spectrometry to differentiate b/n microbes
• adv: cheap, reliable, simple to use, quick
• disadv: can’t tell what type of strain the bacteria is, only species

Question 14

PCR advantages and disadvantages

Answer 14

• adv: amplifies specific region of DNA so sensitive and specific
• disadv: can only use on DNA so need to use reverse transcriptase for retroviruses, for new pathogens we need to sequence whole genome to find the target region because otherwise we can’t design primers

Question 15

light microscopy adv + disadv

Answer 15

• adv: useful for bacteria, parasites, amoeba, yeast and fungi b/c can see them
• disadv: can’t see viruses b/c too small, can’t always differentiate between types or strains of a microbe

Question 16

culturing adv + disadv (as a diagnostic test)

Answer 16

• adv: can isolate bacteria from a larger sample, you can check if they’re resistant to antibiotics
• disadv: some microbes take too long to grow on a plate and Pt will be too sick by then, need to have very specific medium and swab for conditions of bacteria, doesn’t work for viruses b/c intracellular

Question 17

serology adv + disadv

Answer 17

• adv: early detection, simple, easily accessible, detect autoimmune diseases, can detect whether there is an active infection or not
• disadv: need to know how to make antibodies to detect complementary antigen

Question 18

adverse affect of fluconazole (anti-fungal therapy)

Answer 18

• drug interactions due to inhibition of CYP450 enzymes