PATHOGENS AND DISEASE

Q. What is meant by the term MICROBE?

A. A very small organism or microorganism, only observed using a microscope eg Bacteria, viruses, microscopic fungi.

A pathogen is:

• A microorganism (microbe) that causes disease.

Athlete’s Foot(Caused by a fungus)

Influenza (flu)

Influenza virus particles

Cholera

Vibrio cholerae bacteria (taken by EM-but can you state what sort?)

AIDS• Acquired Immune Deficiency Syndrome.

HIV =

Human Immuno-deficiency Virus

Syphilis infection

Syphilis Bacteria

Thrush

Candida albicans (the fungus that causes thrush)

Common cold

TB(Tuberculosis)

The pathogen is a bacterium

Polio

Polio viruses magnified65,000 X using an electron microscope(EM)

• Use p4 Textbook to write down the 4 criteria needed for an organism to be classed as a pathogen……..

A Pathogen can……

• Gain entry into the host’s body.

• Colonise the tissues of the host.

• Resist the defences of the host’s body.

• Cause damage/harm to the host tissue.

Infection, transmission, disease?

• When a pathogen is transferred from one individual to another

• TRANSMISSION

• Occurs when a pathogen gets into the host and colonises its tissue

• INFECTION

• Occurs when infection leads to symptoms

• DISEASE

• Complete page 24-25 of your handbook and answer Questions 1 - 4 from page 5 of your text book

The Gas Exchange System / or Respiratory System

The Digestive System

Egs: Influenza, Tuberculosis,Bronchitis,Cold,Pneumonia etc….Egs: Salmonella /

Typhoid food poisoning,Cholera,E. coli,Dysentry, etc….

Normal Protection, prevents microbes entering by:

• Physical barrier

• pH 6.5

• Mucous layer forms a thick, sticky layer that is more difficult to penetrate.

• Enzymes are produced that break down (lyse) the pathogens

• Stomach acid (HCl) kills microorganisms.

Easy for pathogens to enter because…..

The linings are……

• thin,

• moist,

• sticky,

• have a large surface area,

• have a good blood supply.

Pathogens cause disease by:

1) Damaging host tissues eg:– Viruses can inhibit the host’s DNA, RNA

and protein synthesis.– Many pathogens break down the host’s

cell membranes.– Large numbers of pathogens can just

prevent tissues from functioning.

2). Producing toxins

- toxins are poisons released from the bacteria and these can then travel in the bloodstream.

- eg toxin from cholera bacterium leads to diarrhoea.

Note: Pathogens will differ in the number needed to cause disease

• ANSWERS TO Questions 1 - 4 from page 5 of your text book:

Answers1. What is a pathogen?

2. Why are the digestive and respiratory systems often the sites of entry for pathogens?

A microorganism / microbe that causes a disease.

Diffusion takes place in these systems so this requires them to have a large surface area and a moist, thin, surface which is easy for the pathogen to penetrate.

3. In which 2 ways do pathogens cause disease?

4. Suggest one reason why oral antibiotics are not normally used to treat gastroenteritis and other diarrhoeal diseases.

By damaging host tissues

By producing toxins (poisonous proteins)

A person with gastroenteritis has vomiting and diarrhoea therefore the antibiotic tablet would be unlikely to remain in the body long enough to actually be absorbed.