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Isolation Cultivation and Counting of Microorganisms Assignment PDF

Added on - 31 May 2021

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ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMS IN A CULTURE.ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMSIN A CULTURE.Abstract: Objectives of the experiment.The main purpose of this experiment was to determine the concentration of the colonies from thesample after counting the number of colonies that were formed and multiplying this count by thevolume spread on the pour plate. Moreover, the experiment aimed at enabling the students toisolate microorganisms from samples using various plating methods like pour plating and surfacespread plating method and also by using the most probable number technique. The experimentalso aimed at enabling the students to know the direct counting methods that they could use tocount the number of microorganisms in the culture. The students were to learn how to use ahaemocytometer. The haemocytometer is an instrument that counts the microscopic particles,.They were also to learn how to use a spectrophotometer in checking the turbidity of the culturein order to estimate the number of viable cells that were present in the sample. Lastly, thestudents were to learn how to prepare dilute series which they would use in their experiment.
ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMS IN A CULTURE.Introduction.According to Sagar Anyal (2016), “Spread plate technique is the method of isolation andenumeration of microorganisms in a fixed culture, and distributing it evenly.” The techniqueseparates microbes contained within a small sample volume which is spread over the surface ofan agar plate, using a sterile L-shaped glass rod to ensure even distribution of the colonies inorder for them to form evenly on the agar surface. Small beads may also be used in place of theL-shaped glass rod to evenly spread the sample over the agar plate to allow for uniform growthof the culture. The plate that is used in spread plating is required when dry and when it is at roomtemperature, in order to ensure that the agar is able to absorb the microbes especially bacteriamore rapidly. The spread plate technique is used for viable plate counts, moreover, it is also usedto calculate the cell concentration in the test tube, from which the sample was plated, and finallyit is used in the enrichment, selection and screening of experiments. Enrichment is important inthe case where the microbe under study exists with another microbe that tends to overgrow I theculture and hence to suppress the growth of the unwanted microbe, the desired microbe isenriched with nutrients that enable it to grow in large colonies. Despite the numerous uses, themethod faces some limitations which include: the method favors the rapid growth of aerobes andfacilitates slow growth of micro aerophilic organisms. Also, the colonies in this method cloudand therefore this makes enumeration quite difficult.
ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMS IN A CULTURE. plate method on the other hand is a method that involves the counting of the number ofcolonies forming the microorganisms that are present in the liquid specimen. In this method, themicrobes grow both on the surface and within the medium. According to Tankeshwar (2016), thecolonies that grow within the medium are generally small sized colonies that may be confluentwhereas the few microbes that grow in the surface of the medium (agar), are of the same size and
ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMS IN A CULTURE.appearance as those on the streak plate. The number of microorganisms present in this particulartest sample is determined by the formula:Colony Forming Unit (CFU)/ml = CFU × dilution factor × 1/ aliquotThe pair plate method is more efficient in counting the bacteria, however, it gives lower countsbecause heat sensitive microbes may die when they come into contact with the molten agar.The difference between the pour plate technique and the surface spread method are that for thepour plate method, the microorganisms are in a liquid sample whereas for the surface spreadmethod, the microorganisms are in solid samples. In addition to that, for pour plate method, thecultures grow within the media and on the surface on the media whereas for the surface spread
ISOLATION, CULTIVATION AND COUNTING OF MICROORGANISMS IN A CULTURE.method, the culture grows only on the surface of the media. This indicates that the pour platefavors the growth of both anaerobic and aerobic microbes whereas the surface smear methodonly favors the growth of aerobic microbes that require air for growth.
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