We use several techniques to identify micro organisms. These include the following:
• Observing the form and structure of micro organisms through a microscope. A light micro scope (magnification 1000x) may be used in the case of most micro organisms. The form and structure of viruses, however, can only be studied through an electron microscope (magnification 1000 000 X)
• Staining micro organisms with various types of stains and observing their reactions through the microscope. Simple stains like methylene blue and crystal violet bring out the size, shape and cell arrangements of the micro organisms. Differential stains bring out structures like flagella, capsules and spores. An important differential stain is the Gram's stain. It divides bacteria into two groups: purple gram positive bacteria and red gram negative bacteria.
• Characteristics of colonies formed on various types of culture media.
• Oxygen requirement of of micro organisms, especially bacteria. Those that require oxygen are aerobes and those that can only grow and multiply in the absence of oxygen are known as obligate anaerobes. Many, however, can grow in the presence or absence of oxygen and are known ad facultative anaerobes. Anaerobes can form colonies within the nutrient agar medium, and not just on the surface.
• Biochemical tests to determine the activities of micro organisms, thus helping to identify those that look very similar. A common biochemical test is the fermentation of simple sugars to produce had and acids.
The general properties of some virus groups that infect animals. It helps to identify the main groups of bacteria that are found in our environment. An example of a blue alga is Nostoc found in moist soil. Protists include
• plant like unicellular organisms like diatoms, chlorella and chlamydomonas, and
• animal like ones like amoeba, paramecium, trypanosoma and plasmodium.
Common fungal micro organisms are the moulds and yeasts. Algae include Spirogyra and volvox.
