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Wednesday, 21 November 2018

Control of Micro Organisms

To prevent infectious diseases from spreading , we have to kill or inhibit the growth of disease causing micro organisms. This can be done through sterilization methods which kill or remove all micro organisms from the objects that are being treated. High temperature and chemicals like chlorine are effective sterilizing agents. Sterilization methods are drastic and so they cannot be used on many objects and living organisms. In these instances, milder methods are used. Chemicals like disinfectants, antiseptics and antibiotics kill or prevent the growth of mainly pathogenic micro organisms. Preservation techniques prevent food spoilage and growth of pathogens in medicines and other products that we use on or in our bodies.

   Some of the common methods of controlling the spread of disease causing agents are through

• high temperature
• antiseptic
• antibiotics
• high salinity
• dehydration.

• High temperature

Most micro organisms that cause diseases in humans grows and multiply around 37°C, the normal human body temperature. at low temperatures they are killed. Thus we can get rid of pathogenic micro organisms

• in food by cooking it properly
• in water by boiling it
• in contaminated objects by boiling them for 30 minutes , heating them in an oven at 160°C (dry heat), or heating them in an autoclave (moist heat).

Pathogenic micro organisms in milk are killed by pasteurization.

Note : an autoclave is an instrument used for sterilizing heat stable materials in the hospitals and laboratories. It sterilizers with saturated steam (at 100 kNm-2). Most pathogenic micro organisms and their spores are killed by 20 minutes.


These are chemicals that kill or inhibit the growth of pathogenic micro organisms. They are usually mild chemicals or dilute solutions of strong chemicals that can be safely applied on body surfaces. Antiseptics are therefore used in cuts, abrasions and wounds on our skin to prevent infection by inhibiting microbial growth. Common antiseptics include alcohol (70%), boric acid and tincture of iodine (2%).

Note : Disinfectant are chemicals that kill or inhibit the growth of pathogens. However , they are stronger chemicals than antiseptics and so are often used in non living things and surfaces. Carbolic acid is common disinfectant used for disinfecting lavatories and floors. It is effective in killing pathogens in faeces, sputum, urine and pis and so is used in hospitals.


These are chemicals which, in low concentration,  can selectively kill or inhibit the growth of most pathogenic micro organisms. Antibiotics are produced by fungi and are not harmful to humans. For  Example, the antibiotic penicillin G is produced By the blue green mould penicillin. This chemical interferes with the synthesis of cells walls in bacteria, especially gram positive bacteria and neissera, and prevents their growth. It has no effect on the cells of higher organisms. Antibiotics like chloramphenicol and tetracycline are effective against both gram positive and gram negative bacteria.

   Generally, Antibiotics are used to control diseases caused by pathogenic bacteria. They are, however, not effective in controlling pathogenic viruses and protozoa.

High salinity 

A high salinity affects the osmotic balance between the microbial cell and it's environment. This inhibits the growth of the microbial cell, and so prevents its manipulation. Washing curs and wounds with salt solution would prevent them from becoming infected. Some foods are also preserved by salting.


Water is essential for the growth and multiplication of micro organisms. Removal of water or dehydration would, therefore, inhibit microbial growth. Many foods are preserved by dehydration methods such as drying.

   Drying in the sun is a practical way of killing disease causing micro organisms in bedding, blankets and clothes. Here, both dehydration and the ultraviolet rays in sunlight kill pathogenic micro organisms.

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