Information for Mr Downie’s 2P6 science class

Microbiology and Disease Summary

Types of Microbes 

There are 3 types of microorganism that you should know about.

Type of Microbe	Named example	Disease caused	Commercial/ industrial Use
Fungus	Yeast	Athletes foot/ thrush,	Bread making/Alcohol production
	Mould	Cause breathing problems / rots food and plant material.	Antibiotics / food production
Bacteria
	Salmonella	Food poisoning
	Lactobacillus		Friendly bacteria found in the gut. Used to produce yoghurt and cheese
Viruses	Rhinovirus	Common cold
	Influenza	Flu (human, bird, swine)

 

Microbial Growth

Temperature

Most microbes will have an optimum temperature (the temperature they grow best at).

As temperature increase growth rate also increases up to an optimum temperature.  At temperatures higher than the optimum microbial growth decreases, and at very high temperatures the microbes are destroyed.

Chemicals

Microbial growth can be reduced or prevented by the use of chemicals. These include antibacterial, antifungal, antibiotics, disinfectants, and antiviral chemicals.

• Antibacterial sprays and handwashes only work on bacteria.
• Antibiotics only work on bacteria.
• Antifungals only work on fungi.
• Antivirals only work on viruses

 

Sensitivity and Resistance

• Not all microbes are affected by chemicals in the same way.
• When a microbe is affected by a chemical (prevents growth or destroys the microbe) it is said to be sensitive to that chemical.
• When a microbe is not affected by a chemical the microbes is said to be resistant to that chemical.
• Microbes can have different levels of sensitivity. Clear zones on a petri dish indicate there has been no growth. The plate below shows 4 discs each with a different antibiotic.
• The clear zones around disc 1 and 3 show that no growth has occurred in that area. The bacteria are therefore sensitive to those antibiotics.
• There is no clear zone around disc 2 and a very slight clear zone around 4. The bacteria are therefore resistant to antibiotic 2 and slightly sensitive to antibiotic 4.

 

Defence Against Disease

The body’s first line of defence

• Your body has a two-line defence system against pathogens (disease causing microbes). Pathogens include bacteria, viruses, toxins, parasites and fungi.
• The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, stomach acid, cilia, urine flow and ‘friendly’ bacteria.
• Pathogenic (disease-causing) microorganisms must make it past this first line of defence. If this defence is broken, the second line of defence within your body is activated.

The body’s second line of defence

If the pathogens are able to get past the first line of defence, for example, through a cut in your skin, and an infection develops, the second line of defence becomes active. Through a sequence of steps called the immune response, the immune system attacks these pathogens.

The second line of defence is a group of cells, tissues and organs that work together to protect the body. This is the immune system.

Cells

The cells involved in the immune system are white blood cells (leukocytes), which seek out and destroy disease-causing organisms or substances.

There are different types of white blood cell. Each of these cell types has a specific function, but they all work together to protect you.

Macrophages: Macrophage means ‘big eater’. These cells ‘eat’ (ingest) or clean up the mess of dead or unwanted cells. They are non-specific and will engulf and destroy any cells or foreign material in the body.

Lymphocytes: These produce antibodies, which recognise and lock onto the antigen (cell marker) of invading pathogens and immobilise them until the macrophage consumes them.

Some of these cells are able to live for a long time and can respond quickly following a second exposure to the same antigen. It is these cells which give us immunity to certain diseases/illnesses.

Vaccines

A pathogen is a disease-causing microorganism.

We are often immunised against a variety of pathogens using vaccines – many of which we receive as children.

Traditional vaccines contain either parts of microbes or whole microbes that have been killed or weakened so that they don’t cause disease.

When your immune system confronts these harmless versions of the germs, it quickly clears them from your body. In other words, vaccines trick your immune system but at the same time prepares it in case the body is infected by the real pathogen in the future.

Examples of diseases which we are immunised against include :

Polio

Diptheria

Whooping Cough

Measles, Mumps, Rhubella

HPV ( Human Papilloma Virus )

Meningitis

Tetanus