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Use of Selective and Differential Media

Purpose

The purpose of this lab experiment is to enhance learners’ understanding of unique bacterial behavior in various media and relevant skills necessary for microorganism identification. This experiment will allow us to use both selective and differential media to identify gram-positive and gram-negative microorganisms. The three types of media used in this experiment include Mannitol Salt Agar, Eosin Methyl Blue Agar (EMD) plate, and MacConkey agar (MAC) plate. Inoculation of the different types of cultures is done aseptically before incubation. Inoculation of the cultures is done by the use of specific loops on the provided media plates for observation and identification.

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Discussion

This investigation illustrates the two types of media used to identify and isolate microorganisms i.e. identification of gram-positive and gram-negative organisms. Although several other methods could be employed for such an exercise, this experiment focuses on two methods: Selective media and differential media. Selective media allows the growth of specific types of organisms while on the other hand differential media allows the development of organisms with shared characteristics including growth patterns.

For this experiment, three types of media were used to identify gram-positive and gram-negative micro-organisms. The media used included the Mannitol salt agar (MSA), Levine eosin methylene blue agar (EMB) plate, and MacConkey agar (MAC) plate. Freshly prepared cultures (Escherichia coli, Micrococcus luteus, and Staphylococcus epidermidis) in broth were used to ensure visible and desired results of the experiment (Carolina 10). All the three cultures were inoculated aseptically in the provided media for purposes of identification based on the reaction of gram-positive or negative micro-organisms. The experiment was completed and set up for observation at specific time intervals. The following observations were made: There were no noticeable changes in the MSA after inoculation of E-coli as no color change was noticed; indicating that it is a gram-negative micro-organism (Carolina 4). Inoculation of Staphylococcus epidermis resulted in the growth of colonies on MSA however no color changes were observed; indicating that it is gram-positive. The lack of color change is due to its lack of enzyme coagulase hence no fermentation takes place (Cindy). Micrococcus luteus produced yellow colonies on the MSA indicating that is a gram-positive organism. The yellow color is a result of acidic properties that turn red MSA to yellow.

Reflection

The three media types employed in this experiment included the Mannitol salt agar (MSA), Levine eosin methylene blue agar (EMB) plate, and MacConkey agar (MAC) plate. They are used in the basic identification of microorganisms both in the medical field and by quality assurance and food inspection bodies. Although both selective and differential media can be used distinctively in the identification process, they often complement each other. These two methods are simple and easy to execute, they also have high accuracy and sensitivity levels however they take considerably longer time.

Works Cited

Carolina Biological Supply. Use of selective and differential media: Investigation manualCarolina Biological Supply, 2017.

Cindy, Mannitol Salt Agar (MSA) Test. Web.

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StudyCorgi. (2022, October 21). Use of Selective and Differential Media. Retrieved from https://studycorgi.com/use-of-selective-and-differential-media/

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StudyCorgi. (2022, October 21). Use of Selective and Differential Media. https://studycorgi.com/use-of-selective-and-differential-media/

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StudyCorgi. "Use of Selective and Differential Media." October 21, 2022. https://studycorgi.com/use-of-selective-and-differential-media/.

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StudyCorgi. 2022. "Use of Selective and Differential Media." October 21, 2022. https://studycorgi.com/use-of-selective-and-differential-media/.

References

StudyCorgi. (2022) 'Use of Selective and Differential Media'. 21 October.

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