Mod 7.1 HSC Biology

Define pathogen

disease causing microorganism

Define infectious disease

Disease (Disruption of a tissue or organ) caused by pathogens

Protozoans characteristics

LIVING

Eukaryotic, single-celled; they move in a variety of means including flagella, cilia, and amoeboid motion.

Complex life cycle, visible with light microscope.

Usually found in water or in moist areas, some are photosynthetic, many are predators, some absorb nutrients

E..g Malaria Plasmodium

Fungi characteristics

LIVING

Both single celled and multicellular

Decomposer - they grow on, break down, and absorb nutrients from dead material

Asexual or sexual spores - spores can be involved in the transmission of fungal disease

Eukaryotic cells will cell wall

E.g. Tinea, Thrush, Myrtle Rust or Panama disease

Bacteria characteristics

LIVING

Single-celled, prokaryotic with cell wall, visible with light microscope.

E.g. Tuberculosis, e.coli

Virus characteristics

NON-LIVING

Smaller in size, non-cellular, DNA/RNA protective coat, not visible with light microscope, requires a living host to grow, Does not multiply in foods, Need only a few viral particles to cause an infection e.g covid-19

Prions characteristics

NON-LIVING

Infectious proteins (no nuclei acids), deceptive form of protein without membrane bound organelles, no DNA/RNA, attacks brain/nerve cells, not visible with light microscopes. e.g mad cow

macroparasites characterisatics

LIVING

Eukaryotic cells, multicellular organism, anthropods or worms, visible to eye.

Covid-19 (cause, symptoms, transmission, management and control)

Coronavirus highly contagious and affects respiratory system.

Symptoms include; fever, sore throat, coughing, shortness of breath. Transmission occurs through direct and indirect contact i.e. Droplet spread caused by talking, coughing sneezing and contaminated objects when the pathogen is picked up from a surfaced and transferred to the mouth.

Management includes: regular testing for any flu-like symptoms, when arriving from overseas immediate 2 week quarantine.

Control: State wide lockdown, boarder closures and travel restrictions internationally and nationally.

Practical Investigation relating to the microbial testing of water and food samples (variables, risk assessment)

Independent V: Samples in agar plate

Dependent V: Amount of microbes in the agar plates

Controlled V's: Same amount of inoculating liquid (2mLs), same amount spread onto agar plates (1 swipe), placed in incubator at same time for same time and temp.

Experimental control: negative control that follows same procedure but doesn't hold a sample.

Risk assessment: glass breakage - cutting hands/in eyes - wear gloves and place in centre of workbench; burns - burnt skin/hair - place busmen burner in middle of table and wear PPE and tie hair back; allergies - anaphylactic/allergic reaction - do not touch food/wear gloves

Practical Investigation relating to the microbial testing of water and food samples (Hypothesis, aim and equipment)

Hypothesis: The greater exposure of the samples to possible microbes i.n.pond water the greater microbial growth will be present on the agar plates. The lower the exposure to microbial growth i.e. distilled water the lower the microbial growth will be present.

Aim: To test amount and type of microbes in different food and water samples

Equipment: busmen burner, 10 x agar dishes, inoculating loops, incubator, controls and foods samples (10mLs), methylated spirits, measuring cylinders x 10

Modes of transmission for indirect, direct contact and vector:

Direct contact; person-to-person e.g. sex, droplet spread e.g. coughing and mother-to-child e.g. microflora from vaginal canal/placenta

Indirect contact;

Airborne transmission e.g. water vapour in air lasting hours, contaminated objects e.g. surface to mouth, food and drinking water from improper treatment e.g. cholera/salmonella

Vector:

mosquitos, fleas, ticks, birds, bats

Pasteur's Contributions

1. Disproved spontaneous generation theory: Swan-necked flask experiment demonstrated that microbes caused decay. Using boiled broth in sterile flasks, one had a swan necked flask and the other was broken which led to microbes contaminating that flask and thus disproving spontaneous generation theory.

2. Developed world's first vaccine for anthrax and chicken cholera (discovered a way to weaken/diluted bacteria for the host to develop immunity) establishing the principle of immunity through an experiment.

3. Demonstrated fermentation by living organisms (yeast) proving yeast responsible for beer and wine thus, creating pasteurisation.

Germ theory experiment

Aim: To demonstrate that microbes were air-borne and did not spontaneously generate

Method:

Flasks with water were boiled to sterilise flasks of any existing microorganisms

Meat broth was boiled in 3 flasks to remove any microorganisms present in broth (control flask with cork stopper, broken swan-neck and swan neck flask)

Put stopper/lids on

Let flasks cool in same environment for 2 weeks

Results:

Control had no microbial growth = valid

Swan-necked flask had no microbial growth or decay

Broken neck flask had microbial growth and decay

Conclusion: Although the air could reach the broth in both the broken and swan-necked flasks, microorganisms could not reach the broth in the swan-necked flask proving the germ theory and debunking miasma (bad air).

Koch's Postulates rules

1. The microorganism must present in all cases of disease

2. The microorganism can be isolated from the host organism and grown in pure culture, such as agar

3. The microorganism grown in the culture when inoculated into a healthy host must cause the same disease

4. The microorganism must be reisolated from the second host and grown again in a pure culture and proven to be the same as the original microorganism isolated from the first host. (All Present, isolated in pure culture, causes disease in healthy host, preisolated grows the same)

Koch's Postulates experiment

Aim: To demonstrate that infectious diseases are caused by specific microscopic pathogens.

Method:

Identified an infected/deceased sheep suspected to have anthrax.

Took a blood sample of the infected organism.

Placed it on a slide

Observed it under a microscope and saw active rod-shaped cells and inactive dormant spores

Grew isolated microorganism in a pure culture, such as agar

Inooculate grown organism into a healthy host

Reisolate microorganism from second host (should now be infected)

Grow in pure culture

Compare to see if its the same microorganism causing the same disease

Results:

The second host developed suspected disease from the microorganism identified by the infected original host

Conclusion: Identified specific pathogens create specific disease.

Explain the cause and/or transmission of an infectious disease using Koch's postulates

For example; 1. identify diseased organism(s), 2. Take a sample of faces, saliva or blood to isolate the pathogen, 3. Grow inoculated sample in a pure culture, 4. Identify a healthy organism, 5. Inject pathogen in healthy organisms, 6. Reisolate pathogen from healthy organism that is now diseased, 7. Grow in pure culture, 8. Compare original pathogen to new pathogen to understand the specific pathogen causes the specific disease.

Cause and effect of plant disease Myrtle Rust

Cause:

Native Flora fungal disease myrtle rust impacting eucalyptus trees and tea trees.

Effect:

Myrtle rust infections cause grey to brown leaf spots on leaves and buds that develop into yellow pustules with masses of spores. Infected tissues may shrivel and die.

Response:

Localised swelling in infected region, leaf distortion causing defoliation and affects developing tissue.

Cause and effect of animal disease Foot and mouth disease

Cause:

HFMD virus

Effect:

Fevers, blisters in mouth and feet of cattle, sheep, goat and pigs. Weakened and debilitates animals which is highly contagious.

Response: Immune system is activated but its highly unlikely the organism can recover from this disease.

Entry into a host

Entry but killed before causing disease

OR

Entry adhesion to cell to 'dock' and invade the cell to cause disease (invasion through mucus membrane, back of throat, lungs -> epithelial cells)

Multiply in host tissues

Resist or not stimulate host defence mechanisms

Damage the host and spread

Bacteria adaptations to facilitate entry and transmission

Adhesion:

- Pili and fimbria

- Adhesins on the surface of the bacterial cell resist washing action of secretions such as urine, mucus, cilia

- Translocation of bacterial proteins cause host cell membrane engulfment of bacteria

Invasins:

- Enzymes break down cell contents

- Capsules resist phagocytosis by host cells

- Chemical strategies to destroy host immune defences

- Toxins are secreted to damage host cells

Virus adaptations to facilitate entry and transmission

Adhesion:

Must enter the nucleus of the host cell to facilitate replication of the viral genome

Viral surface proteins adhere to host cell surface receptors and co-receptors

Invasion:

Viral surface proteins invade using endocytosis to host cell surface receptors.

Receptor-mediated movement of virus into the cell. Enveloped viruses are enclosed within an envelope formed the host cell membrane as they move into cell

Non-enveloped viruses (eg. polio virus) form a pore in the host cell membrane & deliver the viral genome through it

Some viruses use the cells normal membrane-forming processes, follow a route through endoplasmic reticulum and the Golgi body then bud off from the surface

Prions adaptations to facilitate entry and transmission

Entry:

'Piggybacks' proteins to enter through gastrointestinal systems

Transmission:

Direct contact from faeces, soil, food and water.

Protozoans adaptations to facilitate entry and transmission

Entry: Microtubule protrusion and formation of a vacuolar membrane gives protection from lysosomes.

Transmission:

Mosquitoes salivary glands, feeding through blood using saliva thus transmitting to new hosts. In order to improve transmission of malaria (plasmodium).

Macroparasites adaptations to facilitate entry and transmission

Entry:

Specialised mouthparts to attach to host skin to secrete saliva.

Transmission:

Ticks, fleas can jump to new victims easily and birds/bats/mosquitos can fly for fast transmission.

Fungi adaptations to facilitate entry and transmission

Entry:

Assisted by cell wall and capsules to protect attacks to adhere to host cells. Thermotolerance to cope with body temperatures

Transmission:

Spreading microscopic spores in air, inhaled or on skin.