Diseases caused by Bacteria, Fungi and Viruses

IntroductionThe body is constantly surrounded by

microbesIt has many defence mechanisms to

prevent against pathogensThe first defence is to stop pathogens

getting into the body.

Preventing microbes getting into the body

Skin is bacteria proof: Thick outer layer that secretes oils and salt which kills many pathogens

Saliva, stomach acid and tears also contain chemicals to kill pathogens

Immune system: kills many pathogens that gain entry to the body

The Immune SystemSymptoms of diseases develop when the

pathogen reproduces rapidly before it can be destroyed.

Diseases can be caused by microbes. Some are parasites and cause damage by

sapping energy and weakening the living organsism

PesticidesChemicals made to kill unwanted

organisms. Herbicides kill unwanted plants, Insecticides kill unwanted insects and Fungicides kill fungi.

VaccinesOffer protection against some bacterial diseasesCan help the immune system produce

antibodies to fight off particular diseasesSome supply ready made antibodies, most

useful for diseases that kill too quickly for the body to make its own. However in this case immunity only lasts for a certain time like tetanus, therefore you have to get booster shots.

VaccinesViral diseases are hard to manage due to

mutation of the virus. By the time a treatment is discovered the virus has mutated so it is less effective at killing it.

AntibioticsTaken internally as pills or solutions, they

destroy pathogenic bacteria but don’t harm living tissue.

Penicillin is the first antibiotic, but since then many more have been produced.

Bacterial infections were the main cause of human deaths until the development of antibiotics.

AntibioticsProduced by a living organism which

inhibits the growth of other kinds of organisms.

Some kill bacteria, others slow bacterial growth giving the body’s immune system a fighting chance.

Useless against viruses as they have no chemical processes (metabolism)

DisinfectantsPowerful microbe killers.Used to clean toilets, floors etcE.g. Janola, “PINE O CLEAN”

AntisepticsUsed in cleaning living tissue, such as

scratches and woundsE.g. Savlon, Dettol

Resistance to AntibioticsSome strains of bacterial diseases have

developed resistance to antibiotics. This means larger and larger doses of antibiotic are needed to kill pathogens.

Red is resistant pathogens Yellow not resistant

1st step: The original pathogens2nd step: antibiotic taken3rd step: reproduction of

resistant bacteria

QuickTime™ and a decompressor

are needed to see this picture.

Resistance to AntibioticsIf this process happens repeatedly, the

resulting bacteria can be totally unaffected by the antibiotic.

These are commonly called super-bugsSome countries estimate that up to 30%

of bacteria show signs of resistance to drugs normally prescribed for their treatment.

Resistance to AntibioticsHence why when you are given a prescription

you are told to take all the antibiotics even if you get better.

Scientists think that this drug resistance is the result of over prescribing. I.e. prescribing a drug that is more potent antibiotic than needed.

Also when people don’t take the full prescription some bacteria may still be present and survive.

How Bacteria Cause DiseasesBacteria harm the body by killing the

cells they attack. (TB live inside defence cells of the body and attack other healthy cells)

Some of the most deadly bacteria cause disease by producing poisonous substances (TOXINS) as waste products from excretion.

Bacterial disease examplesBotulinus: prevents transfer of signals

from nerve to muscle including breathing muscles. 1g can kill 15 mill humans.

Tetanus: prevents muscles relaxing, after entry into wounds

Cholera: causes diarrhoea, can lead to death due to dehydration

How is Disease SpreadDirect ContactDroplets (colds + flu)Drinking waterFoodInsectsInfected needles and surgical instruments

Summary NotesThe body prevents pathogens entering the body

by: skin, saliva, stomach acid, tears and the immune system.

Treating Diseases:Pesticides:Vaccines:Antibiotics:Disinfectants:Antiseptics:

Use your understanding science book and ESA to fill in

the followingHow resistance to Antibiotics is

developed:

How bacteria cause disease:

How disease is spread: