Microbiology Lab Practical Exam 2 Questions and Answers 100% Pass

Microbiology Lab Practical Exam 2 Questions and Answers 100% Pass Oxidase Test - *Positive Test:* -Turns blue within 20-30 seconds *Negative Test* -No color change within thirty seconds *Reagent used:* -Oxidase What is the purpose of the oxidase test? - -The tests is used to identify bacteria containing the respiratory enzyme cytochrome c oxidase as an electron acceptor in the ETC. How is the oxidase test performed? - 1. Transfer bacterium to the paper 2 100% Pass Guarantee Katelyn Whitman, All Rights 2. Add drops of complex A & B to bacterium 3. Observe for color change within 30 seconds Why should you read the results of the oxidase test within 30 seconds? - -The reagents of this test are unstable, therefore they may oxidize independently shortly after becoming moist. Therefore it is important to read within 30 seconds. Catalase Test - *Positive* -Visible Bubble production *Negative* -No Bubbles *Reagent Used:* -Hydrogen Peroxide 3 100% Pass Guarantee Katelyn Whitman, All Rights Why is the Catalase Test Used? - -This test is used to identify organisms that produce the enzyme catalase, and its ability to break down hydrogen peroxide. How is the catalase test performed? - 1. Transfer a large amount of growth to slide 2. Place one to two drops of hydrogen peroxide on bacteria 3. Observe for bubbles MacConkey Test - *Poor Growth or No growth:* -Organism is inhibited by CV and/or bile, therefore is Gram-positive *Good Growth:* -Organism is not inhibited by CV and/or bile, therefore Gram-Negative *Pink to red growth with or without bile precipitate:* -Organism produces acid from lactose fermentation therefore is a probable coliform *Growth is "colorless" (not red or pink):* 4 100% Pass Guarantee Katelyn Whitman, All Rights -Organism does not ferment lactose, therefore is a noncoliform What does the bacteria look like on a MacConkey Media? - *Negative Growth:* -Streak lines visible, but no colonies (Gram-positive) *Positive For Growth, but colorless:* -Gram-negative, but no lactose fermentation (noncoliform) *Positive for growth and Lactose fermentation:* -Pink growth and good growth indicates a Gra