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ISOLATION OF MICROBIAL PURE, , eC] Rte) 3, , Microorganisms are generally found in nature (air, soil and water) as, mixed populations., , , , Even the diseased parts of plants and animals contain a great number, of microorganisms, which differ markedly from the microorganisms of, other environments., , * To study the specific role played by a specific microorganism in its, , environment, one must isolate the same in pure culture., , » The two major steps of obtaining a pure culture are as follows :, , Firstly, the culture has to be diluted until the various individual, microorganisms are separated far apart on agar surface that after, incubation they form visible colonies isolated from the colonies of, other microorganisms., , Secondly, an isolated colony has to be aseptically picked off the, isolation plate

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a > ' seeeaaossesoemmmnn, ——SS =e a SESE, Pure vs mixed culture, , * Pure: originate from 1, bacteria strain, , , , « All colonies look the same, , , , * Mixed: originate from, many bacteria strains, , Soe, , *« Colonies have different ==, , size/shape, , , , http: //smecd net/accounts/case/biol240/streakplate html

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» Points to be taken into consideration during the inoculation are :, , * The inoculation loop has to be sterilized before every inoculation, of colonies from the agar plate, , * Every time the loop is sterilized by heat it must be cooled before, inoculating the next colony, , * There are several methods of isolating the pure culture of, bacteria, like, streak plate method, pour plate method, spread, plate method and serial dilution., , Why important ?, Pure cultures are important in microbiology for the following reasons, , ** Once purified, the isolated species can then be cultivated with the, knowledge that only the desired microorganism is being grown., , ** A pure culture can be correctly identified for accurate studying, and testing and diagnosis in a clinical environment., , ** Testing/experimenting with a pure culture ensures that the same, results can be achieved regardless of how many time the test is, repeated., , ¢ Pure culture spontaneous mutation rate is low, , * Pure culture clone is 99.999% identical

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* The process of screening a pure culture by, separating one type of microbes from a mixture is, called Isolation., , Some common isolation methods are;, , ¢ |) Streak plate method, , Il) Pour plate method-a) Loop dilution technique, b) Serial Dilution technique, , Ill) Spread plate method, , IV) Micromanipulator method, , V) Roll tube method

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I. STREAKING OR, , STREAK PLATE TECHNIQUE, , In This method the tip of a fine, structure wire loop called, Inoculation needle consist of a, wooden or glass handle with a, Nichrome wire the end of which is, bend to form a loop is used to, transfer microbes from culture., , The straight wires are similar to wire, loop except they do not have loop., These are used to transfer culture in, colony formed on solid culture, medium., , In such cases, the colony from solid, medium is streaked on the surface, of nutrient agar medium in a sterile, petri dish., , , , , , , , , , , , , , , , , , FEO8 Pearens Prentice Hat tne