Techniques for Isolation of Pure Cultures
i. To perform the spread plate and the streak plate inoculation procedure for the separation of the cells of a mixed culture so that discrete colonies can be isolated. ii. To prepare a stock culture of an organism using isolates from the mixed cultures prepared on the agar streak-plate and/or the spread plate. Introduction
In order to be able to adequately study and characterize a certain microorganism, microbiologists need to separate and isolate this microorganism from the many other microorganisms with which it usually shares its natural environment or habitat; proper and professional execution of bacterial isolation techniques are at the centre of routine activities in any professional microbiology laboratory. The task of the microbiologist is to isolate the microorganism under investigation from the mixed culture of the sample and to create a pure culture. A pure culture is defined as a population of cells which arose from a single cell by repeated cell division. In nature, microbial cultures are mixed and do not segregate themselves by species. Identification relies upon isolating individual colonies. Testing requires pure cultures. As a result isolation technique provides an essential microbiological tool. Following ways and techniques are used to establish pure microorganism cultures: * Streak plate technique
Streak plate technique is a rapid qualitative isolation method. It is essentially a dilution technique that involves spreading a looful of culture over the surface of an agar plate. An original inoculum containing a mixture of bacteria is spread into four quadrants on solid media. The goal is to reduce the number of bacteria in each subsequent quadrant. Colonies are masses of offspring from an individual cell therefore streaking attempts to separate individual cells. Discrete colonies form as the individual cells are separated and then multiply to form isolated colonies in the...
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