Week 8

Today's Topics:
○ Protozoa

Lecture Topic:
○ Single celled microorganisms
○ No cell wall
○ Shape maintained by ectoplasm
○ My undergo encystation in adverse conditions - not a cell wall, but similar
○ Parasitic protozoa may also encyst when changing hosts (different life parts of life cycle) (eg Plasmodium)
○ Chemoheterotrophs.
○ Use phagocytosis to take up nutrients.
○ Classification based on shape, presence or absence of cilia or flagella.
○ Some may also use locomotive pseudopodia.
○ May reproduce sexually and/or asexually.
○ Example: Cryptosporidium spp. - found in cattle. Oocysts defaecated, and can end up in water supply if raw or insufficiently treated. Cryptosporidosis can cause diarrhoea when merozoites multiply within cytoplasmic membrane (not intracellularly). This can be persist in immunocompromised individuals.
○ Example: Toxoplasmosis, caused by Toxoplasma gondii. Usual life cycle is oocysts defaecated by cats, and after 3-4 days, sporozoites develop, which are eaten by mice. Sporozoites become haploid trachyzoites, which infect cats when they eat the mice. Exposure to oocysts can infect humans, causing problems in pregnancy or if immunocompromised. Effects on foetus may include congenital blindness, brain damage, or even abortion.

○ Eukaryotes vs. prokaryotes
§ Nuclear membrane
§ Histones & non histones
§ Mitochondria
§ Golgi
§ Endoplasmic reticulum
§ 80s ribosomes instead of 70s
§ Can have sexual reproduction (meiosis to produce haploid cells)
□ Diploid cell --> meiosis --> haploid cells --> fusion: plasmogamy --> dikaryon --> karyogamy --> diploid zygote.
○ Algae
§ Cell walls: cellulose, pectin
§ Chlorophylls
§ Other pigments (phycobilins)
§ Generally multicellular except Euglynophyta spp.
§ Storage products (lipids, starch, etc)
○ Protozoa
§ Alternate hosts
§ No cell walls
§ Classified by morphology (eg flagella, cilia, pseudopodia)
○ Fungi
§ Cell walls: chitin
§ Named according to spores in perfect (sexual) stage.

Medical Microbiology
○ Only 10% of cells in body are human.
○ Microbial flora:
§ Staphylococcus epidermidis - skin
§ Escherichia coli - colon - synthesises vitamins
§ Relationships:
§ Mutualism (both host and microorganism benefit)
§ Commensalism: (latin: at the same table) host neither benefits, nor is harmed. (can be argued to be mutualistic, as presence prevents colonisation by pathogens)
§ Parasitism: microorganism benefits at expense of host. This is associated with pathogens (Greek: suffering makers)
§ Some microbial flora may be opportunistic pathogens if they colonise or replicate in usually sterile areas (e.g. blood, brain, csf, deep tissues)