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Describe the effect a repressor has on the lac operon when lactose is present?
When lactose is present, it binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator region of the lac operon. As a result, RNA polymerase can transcribe the structural genes of the lac operon, leading to the production of enzymes involved in lactose metabolism.
What does starch agar select for?
EMB plate testing is used to look for bacteria with lactose fermentation. + test results show dark purple, blackish or metalic green bacteria colony. On EMB plate, following results showed with 4 different bacteria. * E. aerogenes: Purple colony (+) * E. coli: Metalic green colony (+) * S. aureus: No growth (-) * S. facealis: No growth (-) With the result, we can conclude that lactose fermentation occured by E. aerogeneus and E. coli.
What bacteria produces green colony with white puffy margin on Macconkey agar plates?
Green colonies are a result of a protein called biliverdin or sometimes a variation just called hemolytic verdin. It is a result of incomplete hemolysis of blood, and is produced by any member of the pneumoniae family. If you see green bacteria on MacConkey, it is a form of penumoniae.
What are the MacConkey test results for s epidermidis?
Staphylococcus epidermidis is a gram-positive bacterium and does not ferment lactose. Therefore, on a MacConkey agar plate, S. epidermidis would appear as colorless, indicating a negative result for lactose fermentation. Additionally, there would not be any pink or red colonies representing acid production.
Why are some organisms positive in the ONPG Test but negative when tested for the ability to metabolize lactose?
In the ONPG test, organisms may be positive due to the presence of beta-galactosidase enzyme, which cleaves ONPG and produces a yellow color. However, in the lactose fermentation test, some organisms may lack other necessary enzymes or transport systems to fully metabolize lactose, resulting in a negative result despite having beta-galactosidase.
What happens to lac repressentors in E coli when lactose is present?
When lactose is present in E. coli, it is converted into allolactose, which serves as an inducer that binds to the lac repressor protein. This binding causes a conformational change in the repressor, preventing it from attaching to the lac operon’s operator region. As a result, RNA polymerase can access the promoter, leading to the transcription of genes involved in lactose metabolism. This process allows the bacteria to utilize lactose as an energy source.
What does a LC stool culture show?
A lactose (LC) stool culture primarily identifies the presence of lactose-fermenting bacteria in the gastrointestinal tract, particularly focusing on pathogens like E. coli and other enteric bacteria. The results can indicate an infection or imbalance in gut microbiota. A positive result may suggest a bacterial cause of diarrhea, while the absence of such bacteria can help rule out certain infections. Overall, it aids in diagnosing gastrointestinal illnesses.
What happens when you make curd from milk?
When you make curd from milk, the milk ferments due to the introduction of good bacteria like Lactobacillus. This bacteria converts the lactose in the milk into lactic acid, which thickens the milk and gives it a tangy flavor. The result is a creamy, tangy product known as curd or yogurt.
Which bacteria gives raffinose utilization test?
The bacteria Escherichia coli gives a positive result for the raffinose utilization test. This test is used to differentiate between bacterial species based on their ability to ferment raffinose, a trisaccharide sugar. If an organism can ferment raffinose, it will produce acid and gas, causing a drop in pH and the release of bubbles in the medium.
Which of the following involves a chemical change combinding an acid and a base dew forming or souring milk?
Souring milk involves a chemical change where lactic acid is produced by the fermentation of lactose in milk by bacteria. This is not the result of combining an acid and a base, but rather the conversion of lactose (a sugar) into lactic acid.
What is in milk that makes people lactose and tolerant?
Milk contains lactose, which is a sugar made up of glucose and galactose. People who are lactose intolerant lack sufficient amounts of lactase, the enzyme needed to break down lactose into these simpler sugars for digestion. As a result, when lactose is consumed, it can lead to gastrointestinal symptoms such as bloating, gas, and diarrhea. In contrast, those who are lactose tolerant produce enough lactase to effectively digest lactose without discomfort.
What are coliform bacteria?
A coliform count is a microbiological assay of the number of coliform-type bacteria living in a certain sample. This is often used as a measure of fecal contamination of water supplies.
Is glucose in lactose free milk?
Yes, lactose-free milk contains glucose, but it is not present in its original form. Lactose, the sugar found in regular milk, is a disaccharide composed of glucose and galactose. In lactose-free milk, the enzyme lactase is added to break down lactose into its constituent sugars, glucose and galactose, making it easier for people with lactose intolerance to digest. Thus, while lactose itself is absent, glucose is a result of the breakdown process.
Does lactose can give a positive result in xanthoprotein test?
nitration of the benzene ring and gives positive
What does a K result from a phenol red lactose tube indicate?
A K result from a phenol red lactose tube indicates that the organism being tested is unable to ferment lactose. In this case, the medium remains red, signifying that no acid was produced and there was no change in pH. Additionally, there may be no gas production, as the test typically checks for both acid and gas byproducts of fermentation.
What is the positive result for mucic acid test?
Yes! :D Lactose is a dimer (molecule made of 2 similar units) of glucose and galactose. Mucic Acid is a result of the nitric acid oxidation of galactose. So since one of the monomers of lactose is galactose, it will give a positive mucic acid test.
Ability of bacteria to produce insulin was result of?
Genetic engineering of the bacteria.
