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Escherichia coli and Campylobacter jejuni are some of the common causes of bacterial gastroenteritis. Gram-negative enteric bacteria are a common cause of bacterial gastroenteritis, which is characterized by diarrhea, vomiting, and abdominal cramping. In intensive care units, testing multi-drug resistance in gram-negative bacteria is an important surveillance measure. Another example is the addition of antibiotics for testing drug resistance. MAC is essentially a versatile foundation, in which additional substrates, such as sorbitol, can be incorporated for further differentiation. Many pathogenic gram-negatives can be differentiated by MAC, especially bacterial gastroenteritis causing species. MAC is one of the widely used growth media as it can work to selectively grow gram-negative bacteria and further differentiate them based on their fermentation profile. Typically in a clinical setting, the collected sample is placed on a panel of many growth media for identification and isolation of bacterial cultures. MAC's selective and differentiating properties as a culture medium allow isolating colonies of pure bacterial culture from a source sample. It is still widely used in the clinical laboratory to identify causal agents from a patient (i.e., stool sample).Ī pure bacterial culture remains crucial to assess its virulence, its susceptibility to antibiotic therapy, and its genome sequence in order to facilitate the understanding and treatment of caused diseases. This makes MAC a powerful tool in differentiating and isolating bacterial species from the sample source. MAC is one of the many bacterial cultures clinical microbiologists utilize for diagnostic testing. Altogether, MacConkey agar only grows gram-negative bacteria, and those bacteria will appear differently based on their lactose fermenting ability as well as the rate of fermentation and the presence of a capsule or not. The rate of growth is also a way to further differentiate organisms in the MAC medium. Lastly, some species that forms a capsule appear differently. Therefore, lactose-fermenting-gram-negatives (lactose-fermenters) will form pink colonies, while non-lactose fermenters will form off-white opaque colonies. Even within lactose-fermenters, species will show a varying rate of growth. MAC contains a pH indicator that turns pink under acidic conditions. The fermentation of lactose produces organic acids, particularly lactic acid, which decreases the pH of the agar. The selective and differentiating properties of MacConkey agar enables utilization for both research and clinical applications. MacConkey agar is a selective and differentiating agar that only grows gram-negative bacterial species it can further differentiate the gram-negative organisms based on their lactose metabolism. MacConkey agar (MAC) is a bacterial culture medium named after bacteriologist Alfred T.
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