Identification Of Bacteria Through Selective And Differential Media

Hemolytic Responses through Blood Agar Media

The utilization of blood agar media to observe hemolytic responses is a highly effective method for identifying bacteria, especially streptococci (Marques-Garcia 2020). The following are the several forms of hemolysis:

• Alpha (α) Hemolysis:All around colonies, an unclear zone of incomplete disintegration of red blood cells appears, frequently associated by a green to brown staining of the media. S. pneumonia, as well as many other streptococci related to oral transmission, include hemolytic bacteria.
• Beta (β) Hemolysis:All around the colonies formed, a clear, colourless zone develops, indicating that the Red Bloods Cells have been entirely lysed. Streptococcus pyogenes, Streptococcus agalactiae, and numerous different streptococci subspecies are hemolytic (Marques-Garcia 2020). Several bacteria apart from streptococcus species can be hemolytic, notably Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes, and hemolytic responses are valuable screening tools for bacteria. 
• No (γ) Hemolysis:The colonies produce no visible hemolytic function or discolouration. This type of hemolysis is also known as gamma hemolysis.

Selective media has substances that avoids some microorganisms from growing while supporting others to thrive at the same time. The elevated salt level for mannitol salt agar, such as when it inhibits the development of many microorganisms yet allows staphylococci to proliferate (Knobloch-Westerwick, Westerwick and Sude et al. 2020).

Differential media has differential substances that supports groupings of microorganisms to become visibly discriminated through the look of the colonies or accompanying media, due to a differential among the two sets. One sort of differential media is blood agar that helps bacteria to be identified according to the form of hemolysis they cause. Many common enteric agars, like MacConkey & EMB agars, primarily include selective with gram (-) coliforms and distinguish lactose-fermenting and non-lactose fermenting bacterium (Knobloch-Westerwick, Westerwick and Sude et al. 2020).

MacConkey Agar can be used to isolate samples of E.coli from a contaminated sample of Lettuce. MacConkey Agar is a selective and differential media containing bile salts and crystal violet pigment that is beneficial in contrasting gram-negative bacteria such as E.coli by differentiating lactose fermenting and non-fermenting species. Chooses the best for non-meticulous gram-negatives; red colonies suggest lactose fermented, whereas white colonies suggest no fermentation (Jung and Hoilat 2021).

Thayer-Martin Agar and Chocolate agar will be used to identify gonorrhoea suspected patients (Mowlaboccus 2018). Both these media are enriched.

• Thayer-Martin Agar:

They are the antibiotic-rich and selective medium that includes colistin (which destroys total gram-negative coliform), vancomycin (which destroys gram-positive bacteria), and nystatin (which destroys fungus). Inpatient specimens comprising vast quantities of commensal bacteria, like the female vaginal tract, this type of medium is preferable to choose for intolerant organisms like N. gonorrhoea.

• Chocolate Agar:

The main purpose of using chocolate agar is to Culture picky organisms like Neisseria gonorrhoeae since chocolate agar supports the growth of organisms that would not thrive on a normal medium (Mowlaboccus 2018).

No, a sample collected from a patient’s wound presumed to be affected with MRSA cannot be grown on EMB. Blood agar, mannitol salt agar, and Baird-Parker agar bearing methicillin alone or other antibiotics have typically been used to isolate MRSA (Deniz et al. 2021). The Eosin Methylene Blue Agar is used for selective staining for gram-negative bacteria, so it cannot be used for gram-positive MRSA. Therefore, either of the mentioned agar can be used (Knobloch-Westerwick, et al., 2020).

The Triple Sugar Iron test is a microbial assay that evaluates a microorganism’s capacity to ferment glucose and produces hydrogen sulfide. It is frequently utilized to differentiate enteric bacteria like Salmonella. Since a prolonged incubation period might result in a false negative, TSI Agar media should solely be analyzed after twenty-fours incubation times (Alexan 2017).

The following table shows the color or TSI for salmonella:

Any microorganism with complicated or specific dietary needs is called a fastidious organism. Put another way; a picky creature will only thrive if specified resources are present in its environment. Microbes that will solely develop if specific nutrients are available in the culture medium are fastidious organisms.  As a result, fastidiousness is frequently regarded as impossible to cultivate using any available approach (Lainhart and Burnham 2018).

References:

Alexan, A.F., 2017. Lactose fermenting Salmonella typhimurium, Salmonella stratford and Salmonella blegdam. Egyptian Journal of Agricultural Research, 95(3), pp.1285-1296.

Deniz, N., Bayram, Y., Parlak, M., Irden, ?. and Güdücüo?lu, H., 2021. The determination of meca gene presence in mrsa strains isolated from intensive care unit by conventional, automated and pcr method. Eastern Journal of Medicine, 26(1).

Jung, B. and Hoilat, G.J., 2021. MacConkey Medium. StatPearls [Internet].

Knobloch-Westerwick, S., Westerwick, A. and Sude, D.J., 2020. Media choice and selective exposure. Media effects: Advances in theory and research, pp.146-162.

Lainhart, W. and Burnham, C.A.D., 2018. Enhanced recovery of fastidious organisms from urine culture in the setting of total laboratory automation. Journal of clinical microbiology, 56(8), pp.e00546-18.

Marques-Garcia, F., 2020. Methods for hemolysis interference study in laboratory medicine–a critical review. Ejifcc, 31(1), p.85.

Mowlaboccus, M., 2018. Molecular Epidemiology of, and Antimicrobial Resistance in, Pathogenic Neisseria meningitidis from Western Australia.

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