Microbiology Lab Practical Questions and Answers Already Passed

Microbiology Lab Practical Questions and Answers Already Passed What is the purpose of the aseptic technique in the microbiology lab? To prevent contamination of samples and the environment. What is the primary function of the streak plate method? To isolate individual bacterial colonies. What color do Gram-positive bacteria appear after a Gram stain? Purple. What is the role of the iodine solution in the Gram stain process? To act as a mordant and fix the crystal violet to the bacterial cell wall. What is the purpose of using immersion oil with a 100x objective lens? To reduce light refraction and improve image clarity. 2 What is the key structural component of Gram-positive bacterial cell walls? Thick peptidoglycan layer. What is the purpose of the acid-fast stain in microbiology? To identify bacteria with waxy cell walls, like Mycobacterium species. What is the first step in preparing a bacterial smear for staining? Applying a thin layer of bacteria onto a slide and allowing it to air dry. What does a positive catalase test indicate? The presence of the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen. What is the main function of selective media in microbiology? To inhibit the growth of certain organisms while allowing others to grow. What does a zone of inhibition in the Kirby-Bauer test represent? The effectiveness of an antibiotic against a specific bacterium. 3 What is the purpose of using a control in microbiological experiments? To provide a baseline for comparison and validate the results. What type of bacteria require oxygen for growth? Obligate aerobes. What is the function of a Durham tube in a fermentation test? To capture gas produced during fermentation. What does a pink result in a urea hydrolysis test indicate? The presence of the enzyme urease, which hydrolyzes urea into ammonia. What is the appearance of lactose-fermenting colonies on MacConkey agar? Pink or red colonies. What is the role of heat fixation in preparing bacterial smears? To kill the bacteria and adhere them to the slide. 4 What is the purpose of the coagulase test in microbiology? To detect the production of coagulase enzyme by bacteria like Staphylococcus aureus. What does a green sheen on eosin methylene blue (EMB) agar indicate? Strong lactose fermentation, often by E. coli. What is a common sign of contamination in a bacterial culture? The presence of unexpected colony morphologies.