What is the difference between chemically defined and chemically complex media? Give either a clinical or environmental research example for which each media type would be the most appropriate choice...

1. What is the difference between chemically defined and chemically complex media? Give either a clinical or environmental research example for which each media type would be the most appropriate choice for culturing microorganisms.
The chemically defined media is the type of media in which the composition of each and every constituent is fixed and known while a chemically complex medium is the one in which the composition of the constituents is not known. During the laboratory experiments for growing microorganisms glucose broth (chemically defined) is used to enhance growth of certain microorganism. While, nutrient broth (chemically defined) medium is used to support the growth of several microorganisms (Speratto et al., 2021).
2. Why is differential media typically inoculated with isolated colonies that have been previously cultured on general growth media?
General growth media is first used to support the overall of microorganisms of any type in the culture. However, isolated colonies which have certain induced properties will be able to grow in differential media only. The differential media will have components which allow the growth of only the organisms from the isolated colony and no other microorganism. For example, MacConkey agar contain certain components which enables the growth of gram negative organisms only and hence it helps in differentiating gram positive bacteria from gram-negative bacteria (Lee at al., 2010).
3. Use a textbook or a reputable internet source (such as www.cdc.gov) to research and describe a scenario in a lab or clinical setting in which a selective and/or differential test would be necessary
The selective media is used to favor the growth of only selected microorganisms in a culture. For example if the selected organism has the ability to survive even in presence of ampicillin, then a selective media will be used which contain ampicillin and hence will support the growth of ampicillin resistant organisms only and kill all the other organisms in the media. The differential media are used to distinguish one media from another which has the tendency to grow on the same media. Here, biochemical characteristics of an organism is used to differentiate one type from another. Example of differential media is blood agar, this media will differentiate organisms on the basis of their ability to lyse red blood cells (Tallwalker et al., 2004).
4. Using a textbook and a reputable online source (such as the CDC), research and describe some potentially pathogenic members of the intestinal bacteria family Enterobacteriaceae. Which pathogenic species are lactose fermenters that will grow on MacConkey agar?
Enterobacteriaceae are a class of gram negative bacteria which are generally found in the gastro-intestinal tract or gut of any organisms. Some of the pathogenic organisms of the same class are entrobacter, salmonella, E.coli, and Klebsiella. MacConkey agar media will be used to differentiate these bacteria as some of the bacteria do not ferment lactose and hence will be able to grow. Hence, the organism which will be able to grow on MacConkey media is salmonella (Lee et al., 2010).
5. Use a reputable internet source to research and describe some potentially pathogenic intestinal bacteria that do not ferment lactose that will grow on MacConkey agar.
The bacteria that do not ferment lactose and will grow on the MacConkey agar are Salmonella, shigella and proteus.
6. Use a reputable internet source to research and describe what variations of MacConkey agar can be used to detect other species of bacteria.
MacConkey agar is a selective as well as differential medium that is used to select a particular organism from a group of several organisms. It consist of condition that will allow the growth of gram positive bacteria who can ferment only (Lee et al., 2010).
7. Look up the formula for MacConkey agar either in a microbiology textbook or online. Is this a chemically defined or a chemically complex media? Why is that important.
MacConkey agar is a chemically complex media and it is used to support growth of certain fermenting microorganisms. The formula for MacConkey agar is
Enzymatic digestion (Gelatin) – 17 g/L, Enzymatic digestion (casein) - 1.5 g/L, Enzymatic digestion (animal tissue) - 1.5 g/L, Lact0se – 10 g/L, bile salt mixture – 1.5 g/L, Sodium chloride – 5 g/L, Natural red – 0.03 g/L, crystal violet – 0.001 g/L and agar – 13.5 g/L
In addition to defined components such as crystal violet and sodium chloride, there is presence of components such as enzymatic digestions of animal tissues and proteins which makes the media chemically complex (Allen et al., 2005).
8. What is a model organism, and why is Saccharomyces cerevisiae so often used as one?
A model organism is the organism which is widely used for studies due to their property of easy and precise studies. Saccharomyces cerevisiae is used as a model organism as it is very easy for genomic manipulation and this organism share many similarities with higher eukaryotes hence increase the credibility of the studies (Hartwell et...