Question

2/24 Finish Standard Poule Cut U Movie: Louis P Introduction to Start Ex Dichotomas in several labs, pH indicators were incorporated into the media. What is the purpose of adding pH indicators, and what products were you looking for? 7. Gas production was featured in several of the labs. How did you visualize gas production? 8. You run a series of metabolic tests on an unknown bacterium and compare results to known metabolic profiles. There is no perfect match because one test result is off. If this test came out the opposite way, you would have a specific answer. What might be going on here? 9. Why are metabolic testing methods, used in bacterial identification, not appropriate for viral identification? 10. Can you envision a way to simultaneously run a series of metabolic tests without having to inoculate individual tubes or plates? Lab 13-Introduction to Metabolic Testing

Answer 1

6. pH indicators are the chemicals or dyes that change color with the change in the pH. pH indicators act as a differential agent to identify or distinguish bacterial colonies on the specific media. Example:

• Phenol Red added in Mannitol Salt Agar (MSA) - to differentiate between coagulase-positive S.aures and coagulase-negative S. epidermidis and micrococci. S.aureus is able to digest mannitol to produce acid, which turns the media around the colonies yellow whereas other species do not digest the mannitol and do not change the color of the media.
• Neutral Red added in MacConkey's Agar - Used to differentiate between lactose-fermenting and lactose non-fermenting Enterococcus. bacteria that can breakdown lactose produce acid, forming red color colonies whereas lactose non-fermenters produce pale yellow colonies.

7. Gas production due to bacterial metabolism can be visualized by using the inverted Durham's tube in the test tube. To detect the gas production, the test bacteria is inoculated in the Phenol red carbohydrate broth containing inverted Durham's tube. If bacteria can metabolize the carbohydrate, it produces acid which changes the color of the media and if it generates gas it gets collected and can be observed as bubbles in the inverted Durham's tube.