Free Living Amobae Flashcards
Where does the free living amoebae cause infections in human hosts?
The eye (cornea), the brain, and can potencially infect other tissues and organs
Why are they known as Amphizoic amoebae?
Due to their abiity to exsits within a host or in the enviroment as free-living forms
Where do you find free living amoebae?
They are aerobic bacteriophageous,meaning they primarly eat bacteria and can be found in soil,water, or sewage.
Describe the morphology of Free Living Amoebae.
- 2 basic forms: trophozoite and cyst
- some can be diphasic (can be in the ameboid form or can be in a flagellated stage)
When does Encystment occur in free living amoebae?
Usually occurs under adverse enviromental conditions (this will allow for survival outside of a host)
Describe the trophozoite form of free living ameobe?
- for these guys adhesionn is essencial for locomotion and feeding
- movement is enhanced by higher tempuratures (close to 30 degrees)
- Have amoebastomes (food cups) which are cytoplasmic extensions that facilitate ingestion of bacteria and cellular debris and attachment to surfaces (this has no relation to pathogenisity)
Describe the flagellated stage of free living amoebae.
- the cell changes shape and synthesizes a flagellar apparatus
- this is induced by nutritional deprevation, tempurature, or osmotic shock
- lasts from 2 to several hours
Describe the cyst stage of free living Ameobae.
- enviromentally hardy form
- mucopolysccharide double wall making it resistant to biocides
- has ostioles (pores) that are sealed by mucus plugs
- these are not formed in tissues and are left behind when trophozoites form
Naegleria fowleri
- Diphasic amoeba
- Agent of amoebic encephilitis
- Unbiquitoes and found mostly in freshwater lakes, hot springs, poorly chlorinated pools, and thermally polluted water bodies worldwide (not in sea water)
- cosmopolitan disease (worldwide)
- growth enhancement at high temps (thermophilic organism)
Describe the life cycle of Naegleria fowleri.
- Enters host in amoeboid form through nasal passage through contact with water
- Amoebae travels along the olfactory nerves and through the cribriform plate to the brain
- If no host is found the amoebae will encyst if enviromental conditions are not favourable or become flagellated but will always return to the original form
Describe the pathogenesis of Naegleria fowleri.
- fast and deadly primary amoebic menigoencephalitis (PAM)
- there is extensive cell necrosis which leads to signifigant hemoragges and destruction of the meninges, olfactory nerves, and brain tissue, and there is lots of swelling (edema) which leads to death
What virulence factors doe N. fowleri depend on?
- Nfa1 protein that mediates amebic attachment to target cells
- Amoebastomes (feeding cups) to help directly phagocytose brain cells
- nitric oxide production
- pore formiming proteins
- cytolytic molecules like cysteine proteases, phospholipases, and phospholipolytic enzymes
How do you protect yourself from N. fowleri?
Salination and chlorination of water bodies or dont put head in water bodies where risk is high
How is a lab diagnosis done on N. fowleri?
- microscopy of brain biopsy or CSF
- In vitro culture on lab media (plain agr wih lawn of bacterial growth)
- molecular detection (PCR)
Acanthamoeba culbertsoni
- ubiquitous in enviroment (found in dust, water, etc)
- free living and widely distributed in natural waters (ponds, lakes, hot springs, and oceans)
*Also detected in bottled mineral water, jacuzzi tubs, ventilation ducts, humidifiers, air conditioners, shower heads and bathroom taps - very resistant to chlorination and other biocides (including radiation)
