BIO D171 LAB MICROBIOLOGY Module 9 Final Exam Review Q & A 2024 1. When performing a gram stain on an unknown bacterium, the cells appear purple under the microscope. What does this indicate about the cell wall structure of the bacterium? - A) It has a thin peptidoglycan layer. - B) It lacks a peptidoglycan layer. - C) It has a thick peptidoglycan layer. - D) It has a lipid -rich outer membrane. Answer: C) It has a thick peptidoglycan layer. Rationale: Gram -positive bacteria stain purple due to a thick peptidoglycan layer in their cell walls that retains the crystal violet dye used in the staining process. 2. A microbiology student isolates an unknown microbe that ferments lactose. Which of the following media would best differentiate this microbe based on its ability to ferment lactose? - A) Blood agar - B) MacConkey agar - C) Mannitol salt agar - D) Sabouraud dextrose agar Answer: B) MacConkey agar. Rationale: MacConkey agar contains lactose and pH indicators that differentiate lactose fermenters, which produce acid and turn the medium pink, from non -fermenters. 3. An unknown bacterium tested negative for catalase. Wh at does this suggest about its ability to neutralize reactive oxygen species? - A) It can effectively neutralize hydrogen peroxide. - B) It cannot effectively neutralize hydrogen peroxide. - C) It produces superoxide dismutase. - D) It has an a erobic metabolism. Answer: B) It cannot effectively neutralize hydrogen peroxide. Rationale: Catalase -negative bacteria lack the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen, making them more susceptible to damage from r eactive oxygen species. 4. Which of the following tests can be used to determine the motility of an unknown bacterium? - A) Urease test - B) Oxidase test - C) SIM medium - D) Coagulase test Answer: C) SIM medium. Rationale: SIM medium co ntains semi -solid agar that allows the detection of bacterial motility by observing the diffusion of growth away from the stab line. 5. If an unknown microbe is resistant to penicillin, which of the following mechanisms could be responsible for its resist ance? - A) Alteration of the drug target site - B) Production of beta -lactamase - C) Decreased permeability to the drug - D) All of the above Answer: D) All of the above. Rationale: Bacteria can resist penicillin by altering the penicilli n-binding proteins (target site), producing beta -lactamase enzymes that inactivate the drug, or changing their cell wall permeability to prevent drug entry. Which staining technique is commonly used to differentiate between Gram -positive and Gram -negative bacteria? A. Acid -fast staining B. Simple staining C. Gram staining D. Endospore staining Answer: C. Gram staining Rationale: Gram staining is a differential staining technique that helps in categorizing bacteria based on their cell wall composition. Which of the following is NOT a characteristic of Staphylococcus aureus? A. Coagulase -positive B. Catalase -positive C. Forms pink colonies on MacConkey agar D. Beta -hemolytic on blood agar Answer: C. Forms pink colonies on MacConkey agar Rationale: Staphylococcus aureus is coagulase and catalase positive, and it shows beta -hemolysis on blood agar, not pink colonies on MacConkey
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