Growth of Microorganisms

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Growth of Microorganisms
Culturing is the growing of micro-organisms in prepared media in the laboratory. The prepared medium is called the ‘culture medium’. Bacteria, fungi and algae grow easily in test-tubes, flasks or Petri dishes of culture media. Virus on the other hand, can only grow and multiply inside living cells, so they cannot be grown in a culture medium.
Micro-organisms are able to increase in size and multiply in number of cells. The growth of micro-organisms is measured based on increase in population size rather than increase in cell size. Under favourable conditions (food, adequate temperature and humidity) micro-organisms reproduce asexually by binary fission. Generation time varies from species to species e.g. rapidly growing specie like Escherichia coli can divide every 30minutes.

Two methods are used to measure the growth of micro-organisms;
(i) First Method: This involves inoculating a bacterial sample into a nutrient broth. As the bacterial population increases, the clear liquid medium becomes cloudy / turbid. Increase in turbidity indicates an increase in number of bacterial cells. Turbidity can be measured using a spectrophotometer. Thus by measuring the turbidity of a bacterial culture in nutrient broth at regular intervals, the growth of a bacterial population can be measured.
(ii) Second Method: This involves taking small samples of bacteria from a nutrient broth at regular intervals of time and diluting the samples several times. Each diluted sample is then inoculated onto a nutrient agar medium in a petri dish and incubated. The number of colonies formed in each petri dish is counted and this indicates the number of living bacterial cells in the diluted sample. From this, the actual number of bacteria in the original sample can be…...

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