MC3-4: Eukaryotic microbial pathogens Flashcards Preview

BS1040: Microbiology and Cell Biology > MC3-4: Eukaryotic microbial pathogens > Flashcards

Flashcards in MC3-4: Eukaryotic microbial pathogens Deck (60)
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1

Define 'facultative parasite'

An organism that lives and can complete its lifecycle independent of a host, but may occasionally be parasitic under certain conditions, e.g. when immunocompromised

2

Define 'obigate parasite'

A parasite that cannot lead an independent, non-parasitic existence

3

Define 'opportunistic parasite'

A parasite that takes advantage of certain opportunities to cause disease. Many lie dormant in the host until the immune system is reduced

4

What are the three ways in which a fungus can infect a human? Which are the most common?

  • Superficially (on the skin) – more common
  • Subcutaneously (under the skin) – less common
  • Systemically (multi-organ) – more common

5

What are dermatophytes?

How are dermatophyte infections acquired by humans?

Name two examples of dermatophyte infections.

Dermatophytes are moulds that grow on keratin (e.g. on the skin)

Infection is acquired from people, animals, or the environment, depending on the species

Examples of diseases: athlete's foot, ringworm

6

Why do dermatophyte infections cause a circular wound?

They eat the keratin and then move outwards when they run out

7

What is candidiasis and what causes it?

Oral or vaginal thrush

Opportunistic Candida albicans following antibiotics and T-lymphocyte deficiencies

8

Define 'commensalism'

A relationship between two organisms where one organism benefits from the other without affecting it

9

Define 'polymorphic' and give an example of a polymorphic fungus.

An organism that can grow as both a yeast and as filamentous cells

e.g. Candida albicans

10

What percentage of humans are infected with Candida and where are the most common sites of infection?

80%

Intestine, colon, mouth

11

What percentage of women have had candidiasis and what is the most common cause?

75%

Following antibiotic treatments

12

How can Candida albicans be pathogenic if they are commensal?

If the host has low immunity or if there is a change in natural microbiota of physiology

13

How does Candida albicans cause disease?

It attacks the skin or mucosae and invades tissue by puncturing skin with its hyphae

If nutrient-rich environment, spores are produced and the population doubles in an hour

Biofilms can grow on implantable medical devices

14

What is Cryptococcus neoformans, what does it cause, and how is it acquired?

A yeast, causing chronic meningitis

Probably acquired from the environment, possibly pigeon droppings

15

How does Pneumocystic carinii grow, what does it cause, and what is the route of infection?

Grows intracellularly

Produces serious pneumonia in immunocompromised

Route of infection uncertain, but endogenous and exogenous routes likely

16

Define 'endogenous'

When an organism already carries a pathogen

17

Define 'exogenous'

When an organism does not already carry a pathogen and acquires it from outside

18

What are Aspergillus and what do they cause?

Ubiquitous mould

Causing pulmonary and systemic infections, e.g. allergic aspergillosis (triggering asthma and COPD)

Can cause aflotoxin (a neurotoxin) and aspergilloma (lumps)

19

Why are effective antifungal drugs hard to find?

Many drugs do not differentiate between fungi and humans

20

What are the three ways in which antifungal drugs work? Give examples of each type.

  • Cell wall integrity, e.g. nystatin, amphotericin B
  • Cell wall biosynthesis, e.g. fluconazole, itraconazole, miconazole, terbinafine
  • RNA synthesis: flucytosine (5-fluorocytosine)

21

What diseases can protoxoal pathogens cause in humans?

  • Malaria
  • Toxoplasma
  • Intestinal and vaginal infections

22

Where are Naegleria found?

In warm fresh water, such as cooling towers in nuclear power stations

23

How does Naegleria affect humans?

Infects humans through their olfactory nerve (through the nose)

Ultimately causes a fatal brain disease
(primary amoebic meningoencephalitis or PAM/PAME)

Known as the brain-eating amoeba

24

What is the life cycle of Naegleria?

  • Flagellate stage:
    • A small pear-shaped organism with two flagellae
    • Mobile
    • Stage that infects people who are exposed through water
  • Amoeba form:
    • Occurs after infection
  • Cyst stage:
    • Occurs in response to unfavourable environmental conditions
    • Resistant to harsh environmental conditions

25

Where are Naegleria fowleri usually found?

In warm-water environments

26

What is one of the most common amoebae found in soil, fresh water, and the natural environment?

Acanthamoeba

27

How big are Acanthamoeba?

15-35μm

28

Where are Acanthamoeba found?

In fresh water (e.g. contact lens solution) and salt water

29

How do Acanthamoeba affect humans?

  • They infect humans through contaminating contact lenses/contact lens cases
  • Can also infect broken skin and cause cutaneous disease or even spread to the brain via the blood
  • Can also infect the mucosa and then the brain in a similar way to Naegleria

30

What is the life cycle of Acanthamoeba?

  1. Cysts
  2. Trophozoite (infective)
  3. Amoebae which can enter humans in many ways