SU_BIO2071_W2_Discussion_Baker_A REVISED

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Week 2 Project Ashley R Baker South University Microbiology Lab BIO2071 SU02 Professor: Pejmon Afshar Due: November 5, 2023 Exercise 3: Primary media for isolation of microorganisms. Selective and differential media are two types of growth media used to isolate and show microorganisms. Selective media isolate a particular type of microorganism by giving a specific condition for its growth (Bonnet,2019). Differential media are used to find and differentiate microorganisms from a closely related group with the help of unique growth patterns. The main difference between selective and differential media is their role in the identification of microorganisms. MacConkey agar is considered selective and differential. It is selective because it inhibits the growth of most gram-positive microorganisms because it holds bile salts and crystal violet. It is differential because it has lactose and a pH indicator. Many species of bacteria produce toxic by-products that can destroy red blood cells (Bonnet,2019). Blood agar is a general purpose, enriched medium often used to grow fastidious organisms and to differentiate bacteria based on their hemolytic properties. Thayer-Martin agar is a selective medium used for the isolation of gonococci (Neisseria gonorrhea) from specimens having a mixed flora of bacteria and/or fungi urogenital specimen. Modified Thayer-Martin (MTM) agar is a GC agar base having vancomycin, colistin, nystatin, and trimethoprim lactate (VCNT). MTM would be used over chocolate when concluding if the species is gonorrhea (Bonnet,2019). Exercise 4: Pure bacterial colonies The loop is sterilized even after the agar plate is inoculated to avoid contamination. The loop is flamed repeatedly to certify that no infecting microbes are familiarized into the culture medium. To use the loop again, the inoculating loop is flamed. Pure culture, in microbiology, a laboratory culture having a single species of organism. A pure culture is usually derived from a mixed culture by transferring a small sample into new, sterile growth medium in such a manner as to disperse the individual cells across the medium surface or by thinning the sample manyfold before inoculating the new medium (Bonnet,2020). Both methods separate the individual cells so that, when they multiply, each will form a discrete colony, which may then be used to inoculate more medium, with the assurance that only one type of organism will be present. Isolation of a pure culture may be enhanced by providing a mixed inoculum with a medium favoring the

growth of one organism to the exclusion of others. A bacterial colony is a cluster of bacteria on the agar plate's surface, commonly known colony forming units. They can be distinguished by elevation, texture, size, color. Our air indeed holds a wide range of microbes. Petri dishes should not be kept open to reduce the risk of contamination by air microbes. Cross contamination can occur as a result (Bonnet,2020). The streak process is intended to create a region where the bacteria are so diluted that when each bacterium touches the surface of the agar, it is far enough away from other cells so that an isolated colony can develop. Exercise 5: Pour plate and streaking technique to obtain pure cultures The convenience of pour and streak-plate techniques in culturing clinical specimens is that it is the choice method for counting the number of colony-forming bacteria present in a liquid specimen as opposed to counting cells individually. Key things to see when picking colonies from agar plates include the form, margin, elevation, surface appearance, opacity, and color of the colonies. After finding a colony, whether by eye or under a microscope, you can continue to isolate it (Sanders,2012). These pure cultures are important to microbiologists as they allow for the study of one species without the worry of contamination from other organisms. The kinds of clinical specimens that may yield a mixed flora in bacterial cultures include bacterial wound cultures. The mix in flora is often due to contaminants that come from outer surfaces of the wound (Sanders,2012). Contamination from the environment at the time of inoculation and mutations in a few cells of the pure culture. Reference: Bonnet, M., Lagier, J. C., Raoult, D., & Khelaifia, S. (2019). Bacterial culture through selective and non-selective conditions: the evolution of culture media in clinical microbiology. New microbes and new infections , 34 , 100622. https://doi.org/10.1016/j.nmni.2019.100622 Bonnet M, Lagier JC, Raoult D, Khelaifia S. Bacterial culture through selective and non- selective conditions: the evolution of culture media in clinical microbiology. New Microbes New Infect . 2020;34:100622. doi: 10.1016/j.nmni.2019.100622 Sanders E. R. (2012). Aseptic laboratory techniques: plating methods. Journal of visualized experiments : JoVE , (63), e3064. https://doi.org/10.3791/3064

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