Microorganisms are living organisms too small for us to see with our naked eyes, but which have far-reaching effects on the lives of man, they can only be seen with the help of magnifying lenses.
The branch of biology which involves the study of microorganisms is called microbiology. Some microorganisms are beneficial to us, such as the saprophytic ones that are used in decomposition of organic matter, while some are harmful, those ones are called germs or pathogens.
Microorganisms are found everywhere.
The following scientists worked extensively on microorganisms: Antony Van Leeuwenhoek, Spallanzani, Pasteur, Robert Koch, Lord Lister and Fleming.
Groups/types of microorganisms
Microorganisms include:
1. Viruses
2. Bacteria and blue-green algae
3. Protists (Protozoa)
4. Some fungi
5. Some algae.
Of these, bacteria, viruses, Protozoa and fungi are the most frequently discussed.
Note: viruses have no cell structure, bacteria and blue-green algae are prokaryotes, why protists, fungi and algae are eukaryotes.
Viruses
Viruses are usually seen with the aid of electron microscope. Virus would either contain DNA or RNA. They are meant to cause diseases. Examples are adenovirus, picornavirus, paramyxovirus, coronavirus, togavirus etc.Examples of diseases caused include influenza, HIV/AIDS, mumps, common cold, smallpox etc.
Bacteria
Bacteria are micro-organisms that can be seen easily with the aid of light microscope. They contain DNA.
Types of Bacteria
Bacteria are grouped into two types. These are:
A. Bacteria on the basis of the use of oxygen:
1. Aerobic bacteria: These bacteria require oxygen to respire. Examples are Mycobacterium tuberculosis and Vibrio cholera.
2. Anaerobic bacteria: These bacteria do not require oxygen for respiration. Examples are Clostridium tetani and Clostridium botulinum.
3. Falcultative bacteria: These bacteria can live in the moderate or low or no oxygen. Examples are Helicobacter pylori, Salmonella typhi etc.
B. Bacteria on the basis of their shape:
1. Cocci (singular, coccus): These bacteria have spherical/circular(rounded) shape. The spheres may;
(a) form chains i.e Streptococci (Streptococcus pyogens, that cause sore throat) others are S. viridens.
(b) form bunch or cluster i.e staphylococci (Staphylococcus saprophyticus that causes urinary tract infections, S. aureus that causes food poisoning) others are S. epidermidis.
(c) form groups of two; they adhere/stick together in pairs i.e. Diplococci. (Streptococcus pneumoniae that causes pneumonia)
2. Bacilli (singular, bacillus): These bacteria are rod-shaped, such as Escherichia coli found in the intestines of humans and animals. Such bacteria may be;
(a) chain of rods e.g. Bacillus anthracis .
(b) flagellated rods i.e. those with flagella e.g Salmonella typhi that causes typhoid fever.
(c) spore-former i.e those that form spores in the cells e.g Clostridium botulinum.
3. Spirilla (singular, spirillum): These bacteria have cells spirally twisted or cockscrew shaped. Such cockscrew bacteria could be either ;
(a) spirally rigid, i.e spirillae e.g Spirillum minor found in rats, Helicobacter pylori that causes gastritis. Or
(b) spirally flexible, i.e spirochaetes e.g Treponema pallidum that causes syphilis in humans.
4. Vibrios: These are bacteria with comma-shaped cells. They are rigid curved rod, and are also called comma bacillus. Example is Vibrio cholera that causes cholera.
Protists (Protozoa and protophyta)
They are microscopic organisms. The protophyta include the autotrophic diatoms, dinoflagellates, Chlamydomonas, Chlorela and some Euglena. The Protozoa are the heterotrophic group such as Amoeba (some species such as Entamoeba histolytica causes amoebic dysentary), Paramecium, Trypanosomes(causes trypanosomiasis), Plasmodium(causes malaria).
Fungi
Some fungi are microscopic and some are large enough to be seen. Fungi are either saprophytes or parasites. Those that are parasitic include Tinia that causes ringworm. Some fungi are beneficial to man such as Penicillium notatum which is an antibiotic.
Algae
Algae are microscopic green plants, they live in aquatic habitat. Examples are diatoms, spirogyra, volvox, nostoc etc.
CULTURE
The technique used to grow micro-organisms for study in the laboratory in special media is termed culture. The medium used for growing most micro-organisms consists of:
- Agar, a jelly-like material obtained from sea-weed, and
- Nutrient agar/broth.
NOTE:
1. Viruses can only grow and multiply inside living cells. So they cannot be grown in a culture medium like the other micro-organisms. Other micro-organisms that can be cultured are bacteria, fungi, and algae.
2. Culturing disease-causing micro-organisms are always difficult. Therefore, there is need to enrich the culture media with blood to enrich the nutrient agar.
3. During culture, the culture media are usually poured into sterile petri dishes, or test-tubes kept in a slanting position and covered at once. The main reason for keeping the test-tubes in a slanting manner is to provide a large surface area for micro-organisms growth.
Procedures to Culture Micro-Organisms
The major procedures used to culture micro-organisms in the laboratory are the aseptic techniques. The procedures include:
• Sterilizing culture media and all glassware (that will come in contact with the specimen). Such sterilizing instrument is autoclave. The main purpose of sterilizing is to kill all micro-organisms and spores.
• Flaming all equipment used for the transfer of micro-organisms just before use to avoid contamination by unwanted micro-organisms in the air.
• Keeping all petri-dishes, flasks and test-tubes involved covered, and open them near the presence of blue bunsen flame only when necessary for as short a time as possible.
• Wiping the work area with cloth or cotton wool soaked in a strong disinfectant.
Caution: do not touch bacteria cultures with your bare hands. Always wash your hands throughly at the end of any laboratory exercise. All equipment used must be boiled and washed with a strong disinfectant at the end of the experiment.
To prepare a culture of Paramecia
Place some dry grass in a beaker and cover it with water. Leave the preparation for about five days. This preparation is called an 'hay infusion'. The organisms exist in cyst-form on the grass. After this period, you will see a number of white specks moving about near the surface of the water. These are almost certainly Paramecia.
How to examine the Paramecia cultured:
- obtain a clean microscope slide, use a pipette to draw a drop of water from the beaker containing a colony of Paramecia and place the drop on the microscope slide.
- Cover the drop with a cover slip, and watch how the animal moves. The movement is usually rapid but can be slowed down by entangling the animals in a few fibers of cotton wool placed under the cover slip.
- Examine the organism under the microscope , lift the cover slip slightly and place a little iodine solution under it. This stains the nuclear safety. Replace the cover slip and examine the structure of the animal in greater detail under the light microscope.
- Make a leveled diagram of one Paramecium.
Tissue Culture
The method used to culture the cells of multicellular plants and animals, usually in a single layer of cells on a solid surface or as a suspension in a fluid medium.
Importance of Tissue Culture
Tissue culture is used to study:
1. Hereditary mechanism;
2. Growth and development;
3. Viruses and damage they do cause to cells they affect;
4. Special properties of various types of cells;
5. The nature of specific inherited disorders; and
6. Details of cell structure and metabolism.
Application/Uses of Tissue Culture
1. Production of vaccines against viral diseases;
2. To diagnose defects linked to certain types of mental illness in unborn children;
3. For the culture of viruses;
4. For the production of interferon (an anti-viral protein formed by animal cells that are invaded by viruses);
5. To diagnose inherited disorders.
Classwork
1. List five instruments used/required for the preparation of culture solution.
2. Itemize five precautions to be taken during preparation of culture solution.
Identification of micro-organisms
Students are divided into five working groups, with each group provided with a sterilized petri-dishes containing culture medium.The petri-dishes are labeled A, B, C, and D, to be used to collect micro-organisms from air, pond, river, stream, respectively and the fifth one remain sterilized to serve as control. Observe the petri-dishes under the microscope after 3 days. Record your observation and discuss with the teacher.
Staining
We can observe size, shape, cell arrangements, and cell structures such as flagella, capsules and spores of the microorganisms observed using the following stains:
1. Simple stains like methylene blue and crystal violet to observe size, shape and cell arrangements of the microorganisms;
2. Differential stains like Gram's stain to bring out structures such as flagella, capsules, and spores. The Gram's stain divides bacteria into two groups: purple stained called gram-positive bacteria and red stained called gram-negative bacteria.
Staining procedure
Fix and stain cultured medium microorganisms as follows:
1. To fix, pass a slide quickly across the flame of a Bunsen burner three times. The smear on the slide is then dried on it.
2. Allow slide to cool for 2 or 3 minutes.
3. Stain the slide by addition of a few drops on the smear of any one of the following stains: methylene blue or cotton blue, crystal violet and carbon-fuschin for 2 or 3 minutes.
4. Tilt the slide and allow the stain to run off.
5. Allow 5 minutes for the air to dry the slide.
6. Rinse the slides to clear them of excess stain by running clear water over them gently.
7. Use absorbent paper to dry the slide.
8. View the slide once again and microorganisms will at this time be seen distinctly.
Class Activities
Activity 1: To show that microorganisms are present in our body
Method: Scrape the dirt under the nail with a sterilized knife into a petri-dish or use a tooth-pick or a short piece of washed broom-stick to remove the remain of food around the gum of your teeth. Add five drops of distilled water to the dirt or scrape in the petri-dish (the petri-dish contains the nutrient agar and stir very well with a sterilized needle). Cover it up quickly, and label it petri-dish A. Set-up a controlled experiment containing distilled water and agar solution alone in petri-dish without the scrape, cover and label it petri-dish B. Keep under controlled temperature(room temperature).
Results: After three days, coloured patches are seen on the surface of petri-dish A. Stain it with methylene blue, view it under microscope, different bacteria shape could be seen. Fungi such as Mucor and Rhizopus can be seen. No colour patches are observed in petri-dish B.
Conclusion: Microorganisms are present in our body.
Note: The same method could be employed in determining the presence of microorganisms in food, air and water.
How micro-organisms enter the body.
Pathogenic microorganisms after our body through the following ways:
1. Through cuts, wounds and abrasions on the skin, e.g. Clostridium tetani.
2. Through the nose and mouth, e.g. Influenza virus.
3. Through the mouth and oesophagus, e.g. Entamoeba histolytica.
4. Through direct contact, e.g. Ringworm fungi and the spirocahete (e.g. Treponema pallidium).
5. Through urinogenital tracts, e.g. Neisseria gonorrhoea.
6. Through placenta; a foetus is infected of syphilis and measles through the placenta, if the mother is infected.
7. Through insect bites, e.g. Mosquito bites releases pathogens into the body.
8. Through mammalian bite, such as the case of rabies and lassa fever which are caused as a result of dog and rat bites respectively.
CARRIERS AND VECTORS OF MICROORGANISMS
A carrier of microorganism is any organism that only carries pathogen usually on its body, but does not bring about the development of pathogens within its body e.g. Housefly. A vector is an organism (usually insect or other arthropods) which allows the pathogens to develop within its body and transmits it, hence causing the spread of an infectious disease from one organism to another e.g. Mosquitoes. Examples are:
Vector/carrier Microorganism Disease caused
female anopheles mosquito Plasmodium malaria
Tse-tse fly Trypanosome sleeping sickness/trypanosomiasis
Housefly Vibrio cholera cholera and typhoid
Rat flea/body louse Ricketsia typhus
Aedes mosquito Virus yellow fever and dengue fever
Rat fleas bacterium plague
Dog virus rabies
Activity 2: To show that housefly is a carrier
Method: Kill a housefly using a broom, detach its: A. Proboscis, B. Legs, C. Wings, and D. Hairy abdomen. Place each of A-D on culture medium, in separate petri-dishes. Cover them and label them accordingly. Set up a controlled experiment containing only cultured medium in a petridish. Place in an incubator/cupboard for 3 days. Observe and record your observation using the format below:
Part Colour Pattern of growth General appearance
A (proboscis)
B (legs)
C (abdomen)
D (wings)
E (control)
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