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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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


Define 'obigate parasite'

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


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


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


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


Why do dermatophyte infections cause a circular wound?

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


What is candidiasis and what causes it?

Oral or vaginal thrush

Opportunistic Candida albicans following antibiotics and T-lymphocyte deficiencies


Define 'commensalism'

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


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


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


Intestine, colon, mouth


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


Following antibiotic treatments


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


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


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


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


Define 'endogenous'

When an organism already carries a pathogen


Define 'exogenous'

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


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)


Why are effective antifungal drugs hard to find?

Many drugs do not differentiate between fungi and humans


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)


What diseases can protoxoal pathogens cause in humans?

  • Malaria
  • Toxoplasma
  • Intestinal and vaginal infections


Where are Naegleria found?

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


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


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


Where are Naegleria fowleri usually found?

In warm-water environments


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



How big are Acanthamoeba?



Where are Acanthamoeba found?

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


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


What is the life cycle of Acanthamoeba?

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