Yeasts

Question 1

Name three characteristics of yeasts.

Answer 1

1. Eukaryotic
2. Classical pthogens / environmental saprobes
3. Require pre-formed organic carbon compounds for nutrition

Question 2

Name and give a distinguishing attribute of the three main groups of yeasts.

Answer 2

1. Moulds - multicellular filamentous
2. Yeasts - unicellular, oral/round
3. Dimorphic fungi - capable of changing their growth to a mould or yeast phase

Question 3

What characterises a dimorphic yeast?

Answer 3

Mould at 25c and a yeast at 37c

Question 4

Commonly, how do superficial yeast infection occur?

Answer 4

• skin, hair and nails
• sportspeople
• communal bathing facilities

Question 5

Commonly, how do subcutaneous yeast infections occur?

Answer 5

• traumatic inoculation of saprophytic fungi from soil
• tropical regions
• agriculture workers

Question 6

Commonly, how do systemic yeast infections occur?

Answer 6

• inhalation in endemic areas

- hosts with defective immune defenses

Question 7

How are yeast infections diagnosed?

Answer 7

• history (exposure and symptoms)
• clinical and radiological features
• lab investigations (microscopy, culture, histology, antigen detection and PCR)

Question 8

How are yest infections treated?

Answer 8

• Antifungals (topical and systemic)
• Immune restoration
• Antifungal prophylaxis
• Surgical intervention

Question 9

Name two types of yeasts that cause infection in humans?

Answer 9

1. Candida

2. Cryptococcus

Question 10

What is the epidemiology of candida?

Answer 10

• yeast
• most common invasive fungal infection
• skin, mucous membranes and blood (candidaemia)
• infections are normally endogenous

Question 11

What are the clinical features of candida?

Answer 11

• superficially = skin, nails and mucous membranes of mouth and vagina
• Oral thrush = common in AIDS and cancer patients
• Vaginal thrush = common in diabetes mellitus, antibiotic treatment and pregnancy
• Candidaemia = persistant pyrexia (fever)

Question 12

How is candida managed?

Answer 12

• multiple blood cultures
• superficial = topical antifungal treatment
• invasive = systemic therapy (flucanazole, amphoteracin B and caspofungin)

Question 13

What is the epidemiology of cryptococcus?

Answer 13

• yeast
• aquired by inhalation
• C. neoformans (bird droppings)
• common cause of defining meningitis in AIDS patients
• decreases incidence in developed world (HAART availible)
• high mortality in Africa

Question 14

What are the clinical features of cryptococcus?

Answer 14

• CNS common site of infection (HIV patients) = cryptococcomas in brain and meningitis
• All brain related symptoms (headaches, vomitting, seixures, nausea and confusion)
• Can effect any organ and disseminate (especially if immunocomprimised)

Question 15

How is an infection due to cryptococcus diagnosed?

Answer 15

• CSF sample
• Blood culture
• Microscopy (India Ink staining)
• Cryptococcus antigen test

Question 16

What is cryptococcus treated?

Answer 16

• Amphoteracin B (in RSA) (induction phase)
• Flucanozole (consolidation phase)
• HAART and flucanozole (maintenance phase)