![]() The MacConkey medium is identified as a selective and a differential medium. (2, 6, and 9) Why is MacConkey agar selective as well as a differential? The incubation of MacConkey agar plate makes it susceptible to an increase in carbon dioxide which can significantly affect the growth/reduction of some strains of Gram-negative bacilli. Some strains of bacteria grow poorly in the medium while others fail to completely grow. The best way is to perform a subculture procedure and do confirmation test for final identification. The isolated organisms identified only give a presumptive result. Non-lactose fermenting – Salmonella typhimurium, Proteus species, Shigella, Pseudomonas aeruginosa, and Yersinia.Lactose fermenting – Enterobacter aerogenes, Escherichia coli, and Klebsiella.The very essence of MacConkey agar is to differentiate between lactose fermenting and non-lactose fermenting gram-negative bacteria. The strain of bacteria is identified when using MacConkey Agar. What bacteria are selected for when using MacConkey agar? There is no significant change in the appearance of the medium. Non-fermenting lactose strains – The results are colorless and transparent.The change in color is caused by various factors such as acid production secondary to lactose, neutral red absorption, and change in the color of the dye if the pH level falls below 6.8. Lactose fermenting strains –They grow red/pink and surrounded by acid precipitated bile.How to interpret the result of MacConkey Agar? Pour into the sterile Petri plate and carefully observe what will happen.Autoclave 15 lbs pressure or at least 121 degrees Celsius for about 15 minutes.Bring to boil to completely dissolve the medium.The first step is to suspend 49.53 grams of a dehydrated medium in a liter of distilled water.(1, 3, and 6) MacConkey Agar Test Procedure MacConkey agar is also useful in isolating coliforms and intestinal pathogens that are present in the water, dairy products, and other forms of biological specimens. The purpose of MacConkey agar is to isolate Gram-negative enteric bacteria as well as to differentiate between lactose fermenting and non-fermenting lactose gram-negative bacteria. Image source: What is MacConkey agar Purpose ? ![]() Picture 4: A Petri dish with different types of bacteria. Sodium chloride – It provides essential electrolytes needed for transportation and osmotic balance.A colorless reading means that the pH is greater than 6.8. If the pH level is below 6.8, it turns red. Neutral red – It identifies the pH level.Bile salts and Crystal violet – They inhibit the growth of organisms that belong to the Gram-positive family.Lactose monohydrate – It provides a source of fermentable carbohydrate enabling differentiation to take place.They are a source of nutrients needed for growth such as vitamins, minerals, nitrogen, and amino acids. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |