Lecture 15 Yeasts

Question 1

What is Candida albicans 4 virulence factors?

Answer 1

1. Rapid germination after dissemination
2. Protease (digest tissues)
3. Receptor for binding to tissue matrix and complement (prevent immune attack)
4. Polymorphism

Question 2

Describe the general properties of Candida albicans

Answer 2

Most common pathogenic isolate. In plasma C.albicans forms germ tubes, in tissue it can appear unicellular, pseudohyphae and true hyphae. Infections are opportunistic, normal flora in GIT/urinary tract. Causes UTIs and oral thrush

Question 3

What does Candida glabrata cause and why is it an emerging pathogen?

Answer 3

UTI, meningitis and sepsis. Strains of C.glabrata are losing susceptibility to fluconazole (antifungal agent)

Question 4

Where and what are some of the candidasis infections?

Answer 4

Superficial (babies/elderly)
Localised 
Systemic (any organ)
Oral thrush (C.albicans)
Cutaneous (middle of toes)
Onychomycosis (nail infection)

Question 5

What are the 5 ways to sample candidiasis

Answer 5

Exudates
Biopsy
Swabs
Aspirates
Washes

Question 6

What are the 3 ways to culture candida spp.

Answer 6

SDA agar at 37 degrees - white colonies
Serum (C.albicans forms germ tubes)
Chromogenic agar

Question 7

What are some of the ways to diagnose candida spp.

Answer 7

-ve urease test indicates C.albicans
Assimilation tests (strains assimilate certain sugars)
ChromAgar (species colonies dif colour)

Question 8

What are the general properties, causal agent and virulence factors of Cryptococcus neoformans

Answer 8

Basidomycete yeast, affects immunocompromised people. Causal agent is avian droppings. 
Virulence factors include
Ability to grow at 37 degrees
Large capsule
Survival within macrophages

Question 9

What are the diseases caused by cryptococcus neoformans

Answer 9

Pulmonary - cough, fever
CNS - 85% of cases
Cutaneous - primary (trauma) and secondary (systemic disease)
Systemic - localises to many sites and disseminates from pulmonary infection

Question 10

What are the culture and diagnostic techniques for cryptococcous neoformans

Answer 10

Samples - biopsy, bronchial washes 
Diagnosis - 
Microscopy
Indian ink shows budding yeast with thick capsules
Sabourauds dextrose agar

Question 11

Describe the Latex agglutination test regarding cryptococcous

Answer 11

Antibody coated latex beads clump up in the presence of the desired antigen, which is the cryptococcal polysaccharide capsular antigen.

Question 12

What does the Malasseizia species cause, how it is sampled and diagnosed

Answer 12

Malassezia species causes tinea versicolour (rash) and sepsis. It is sampled by swabs and scrapes from lesions. Can be diagnosed by indian ink, gram stain and 10% KOH. it looks like ‘spaghetti and meatballs’ under microscope.

Question 13

What are the general features of Pneumocystis jirovecii and what diseases does it cause.

Answer 13

Non-filamentous fungal yeast, it inhabits immunocompetent animals without disease. However it causes pneumonia in immunosuppressed hosts (AIDS patients) and has a mortality rate of 10-50%. It cannot be cultured and can be found by indirect fluorescent antibody test and PCR.