Micro-organisms Around us

Micro-organisms otherwise called microbes or germs can be defined as living things which cannot be seen with unaided eye but by the use of microscopes.

They exist almost everywhere, in water, air, soil, surface of objects, as well as on and within living organisms. They are carried by air currents from the earth’s surface to the upper atmosphere. They occur most abundantly where there is food, moisture and adequate temperature for their growth.

Types of Micro-organisms

Micro-organisms include all viruses, bacteria and the protists. Others are the cyanobacteria, certain fungi and algae.

  1. Bacteria: These are minute unicellular organisms or simple association of similar cells which multiply by binary fission. Most bacteria cells range between 0.2 µ-2µ in diameter and 0.0005mm-0.002mm long. Each bacterium cell has a cell wall with cytoplasm. There is no well defined nucleus. Consequently, they are prokaryotic organisms. There are different kinds of bacteria showing a range of shapes:
    • Streplococci: These are arranged in chains. They cause sore throat.
    • Staphylococci: These stick together to form irregular bunches. They cause boils.
    • Diplococci: They occurs in pairs. e.g. pneumococci which causes pneumonia.
    • Bacilli: They is rod-shaped. They cause typhoid fever
    • Spirilla (singular = spirillum): These are rod-shaped bacteria twisted into a spiral shape.
    • Spirochaetes: These are also spiral in shape but are more flexible and slender with helically coiled structure e.gTreponemapallidum which causes syphilis.
    • Vibrios: These are comma-shaped bacteria e.gVibriocholera which causes cholera
  2. Viruses: Viruses are a large group of pathogens whose presence is felt only when they are in contact with living cells. They are very small and vary between 0.1µ-0.25 µ in diameter. The largest virus is less than one-fourth the size of typhoid bacterium. A virus consists of a nuclear material either DNA or RNA, enclosed within a protein coat. Outside living organisms they are like complex chemicals.
  3. Protists: These are single-celled animals, mostofwhich are only visible by means of microscope. They are common in fresh water and moist soils. Examples include Euglena, Paramecium, Trypanosoma, Plasmodium, etc.
  4. Fungi: They are diversified in form. The blue and green growth on oranges, lemons, cheese and the white/grey growth on bread are usually signs of fungal infections. Fungi feed saprophytically. Examples of fungi include Mucor, Rhizopus, Penicillium, Aspergillus, etc.
  5. Algae: Most algae are unicellular and very small. They have chlorophyll. They occur abundantly in water, moist soils, bark of trees, stones, etc. Free floating microscopic algae are referred to as phytoplanktonsand they form the major food of aquatic animals. Examples of unicellular algae include Chlamydomonas and Protococcus.

Culturing

Culturing simply involves the techniques of growing micro-organisms in special media in the laboratory. It involves the making of sterile medium, inoculating, incubating and examining micro-organisms. By this means, micro-organism characteristics such as colour, pattern of growth and appearance can be seen. Culture of micro-organisms can be grown from water, air, animals, plants and various parts of human body.

It is easier to grow bacteria, fungi, and algae in appropriate media. The material on or in which microbes grow in the laboratory is called culture medium. Some media are prepared from complex extracts of plant or animal tissues. A culture is the population of organisms cultivated in a medium.

The preparation of Culture Solution

  1. The culture solution called Agar is prepared under sterile conditions
  2. Then boil and pour it into sterile petri-dish
  3. Allow it to cool and set in the petri-dish
  4. A heat sterilizer may be used to kill micro-organisms in the petri-dish
  5. The material is then introduced into the agar medium and covered immediately
  6. Place the petri-dish in warm but dark compartment or an incubator
  7. Observe and record what you have seen for 2-3 days

Instruments Required for the Preparation of Culture Solution

  1. Micro-scopes
  2. Petri-dishes
  3. Hand lens
  4. Test tubes
  5. Slides
  6. Cover slips
  7. Inoculating needles or loops
  8. Inoculating chamber if available

Precautions

  1. Wash hands with soap before and after the preparation of agar solution
  2. Avoid talking, coughing, sneezing and touching of infected jelly
  3. All instruments should also be sterilized before the beginning of culture solution preparation.
  4. Unused agar should be sterilized by washing with antiseptic soap and disinfectant, e.g. 40% folmadehyde. Heat can also be used to sterilize
  5. A sick person should not be permitted to take part in culturing experiments
  6. Open petri-dish only slightly and cover at once
  7. Close petri-dish firmly with adhesive tape

While bacteria, fungi and algae can be grown in test tubes and Petri dishes in culture media, viruses cannot be grown. They can only grow and multiple inside living cells of an organism. Through Tissue culture, living tissues and cells of multi-cellular organism are cultured in appropriate media and studied. To carry out studies involving viruses, are cultured in the laboratory by injecting the virus into the fertilized Bird egg e.g. egg of duck.

On the culture medium, micro-organisms occur as colonies. Colonies of micro-organism do clump together in large number of organism of the same kind. Colour, appearance other characteristics of the colonies enable the investigator to identify and differentiate microbes in a culture medium.

Identification of Micro-organisms

There are many ways of identifying micro-organisms around us. These include the use of microscopes stains of different types, types of colonies formed by the microbes, their food requirement and oxygen requirement of the organisms.

Microorganism is present around us in the air, water etc. They enter our body, food materials such as boiled rice, fish, bread, milk, fruit. When these food are kept at room temperature for long,they get spoilt by microorganisms. Our body also contains several microorganisms. For instance they can be found in our mouth, teeth, nose, skin etc.

All microbes found in water can be grouped into three as follows:

  1. Soil micro organism (washed into the surrounding water bodies during heavy rains)
  2. Natural water micro-organisms: these are microbes that are naturally found in aquatic habitats.
  3. Sewage micro-organisms

Micro-organisms can be identified in the air, pond water, river and stream by preparing a culture medium. The following procedures should be followed:

  1. Five petri-dishes with culture medium labelled A, B, C, D and E respectively
  2. Expose petri-dish A to air for about 10-15 minutes and then cover it.
  3. Put in petri-dish B a few drops of pond water and cover it
  4. Put in petri-dish C a few drops of river water and cover it
  5. Put in petri-dish D a few drops of stream water and cover it
  6. Allow petri-dish E to serve as control(do not introduce anything into it)
  7. Leave all the petri-dishes in the laboratory for 3 to 4 days
  8. Observe all the petri-dishes for any development and note any difference in each of the petri-dishes
  9. Record the characteristics (colour, pattern of growth, appearance) of colonies of micro-organisms in each petri-dish

Carriers of Micro-organisms

Any agent that carries microbes from one place to another is called a carrier. Carriers can be living or non-living things. Non-living carriers include air, water, and food while animals (e.g. houseflies, mosquitoes, rats, cats, etc) are the living carriers. Animal vectors carry pathogens either mechanically or biologically. In mechanical method, animals carry the pathogens on their bodies where they cannot grow or multiply. In biological method, the vector becomes infected by feeding on the body fluid of infected persons or animals.