BIOD 171 MICRO LAB EXAMS QUESTIONS AND ANSWERS# 1

BIOD 171 MICRO LAB EXAMS QUESTIONS AND ANSWERS# 1 BIOD 171 MICRO LAB EXAMS # 1 1. What three elements are used in an autoclave to sterilize equipment? heat, pressure, and steam 2. What is the minimum temperature an autoclave must be set at to achieve sterile condition? 125°C 3. If you are working in a lab in which an autoclave is not available, and you are pressed for time, which would you chose to best sterilize your equipment? Hot steam or hot air? Explain why you chose your answer. Hot steam is the best choice as you can achieve a sterile environment in a matter of minutes whereas hot air will take several hours to achieve the same effect. 4. What type of incubator is pictured below? Fixed incubator 5. At what temperature is the fixed incubator set to, as presented in the lab video? 37°C 6. At what temperature should you refrigerate bacterial samples? Explain why this is beneficial. 4°C. This temperature slows bacterial growth and prolongs the life of the sample. 7. What are the FOUR types of gloves presented in the lab video? Latex, Nitrile, Thermal cold, Thermal heat 8. What THREE rules were discussed in regards to lab safety that would protect you and others from contamination? 1. Never eat or drink in the lab 2. Always wear appropriate PPE 3. Never leave the lab wearing PPE 9. What are the main sections that should be found in a lab notebook? Name at least 4. Objective, Procedure, Notes, Results and Deviations LAB 2 4. How should you hold the microscope when you move it or carry it? You should hold it with one hand on the neck and one hand under the base 5. List the four magnification strengths found on the objectives of the light microscope shown in the lab video. 4x, 10x, 40x, 100x 6. As you looking through the microscope you notice your sample is slightly off-center—what component of the microscope would be used to bring the sample into the center of the image? Stage adjustment knobs 7. What objective power is best suited if you are uncertain what the sample is and where to begin? 4x (or lowest power objective) 8. You are viewing a sample of bacteria that is 3 mm in diameter through a 40x objective lens. The eyepiece has a magnification power of 10x. What size will the sample appear through the eyepiece? 1200 mm in diameter (or 400x’s larger) 9. Based on the microscope shown in the lab lecture, which objectives would NOT require placing oil on the slide? 4x, 10x and 40xResults: Magnification = objective x eyepiece LAB 3 EXAM 1. List the 4 main steps used to prepare a WET mount and indicate which (if any) step is optional. 1 – Clean slide 2 – Circle area on slide with wax/hydrophobic pen 3 – Apply organism to slide 4 – View under microscope *Note: there are no optional steps in the wet mount. 2. When preparing a glass slide for a dry mount, what cleaning solution was used? 70% ethanol 3. You wish to study the motility of a particular bacterium. What type of mounting technique would you use? Explain your answer. A wet mount technique is the best technique to use when studying motility of an organism because the sample remains viable (heat fixing kills the sample). 4. What dye do Gram-negative bacteria primarily retain? Safranin 5. Why are Gram-positive bacteria able to retain the crystal violet dye? They contain a thick peptidoglycan layer in their cell wall that readily retains the dye. 6. Identify the Gram status (positive or negative) and shape of the bacteria pictured below. Gram- Negative; Bacillus (rod) 7. An acid-fast stain is most commonly used to identify what type of bacterium? What is the name of the primary dye used in this technique? Mycobacterium; carbolfuchsin dye 8. Why do bacteria repel the dye nigrosin? Nigrosin is a negatively charged dye. The membranes of most cells are also negatively charged. The membrane will repel the dye not allowing it to be absorbed. 9. What is one disadvantage of heat fixing a sample? The heat fixing procedure kills the specimen. This also prevents any observations on motility and enzymatic properties. 10. What is the proper way to dispose of all materials used during the lab? All materials must be place in a biohazardous waste bag and placed into an autoclave for sterilization. 11. What are the Gram status, shape and identification of organism #2 from the Gram stain procedure? Gram-negative; Bacillus (rod); E. Coli 12. What are the Gram status, shape and identification of organism #5 from the Gram stain procedure? Gram-positive; Cocci (spherical) chain; Streptococcus LAB 4 EXAM 1. What type of media is best used to eliminate certain bacteria from within a mixed culture? Selective media 2. According the lab module, what type of agar plate is the most commonly used nutrient agar? What color is it? LB agar; Light (or pale) yellow 3. What was the name of the selective agar plate (shown below) that is similar to a blood agar plate? MacConkey agar 4. What type of bacteria does MacConkey agar select for? Gram-negative bacteria 5. Sorbitol MacConkey (SMAC) agar is: A. Selective media B. Differential media C. Selective and differential media D. None of the above 6 .What pathogen is best identified using a SMAC agar? E coli O157:H7. SMAC agar specifically differentiates between non-pathogenic E coli and the pathogenic E coli strain O157:H7. 7. What is the purpose of doing a 4-phase dilution streak? The purpose of a 4-phase dilution streak is to isolate individual bacterial colonies. 8. If you were required to grow 4 types of bacteria on a single agar plate without cross contaminating the samples, what method would you use? Quadrant growth method 9. Based on the 4-phase dilution streaking experiment, in what phase were bacterial isolates (colonies) observed? Individual colonies were observed within Phase 3. 10. Identify the plating method (below) as demonstrated in the lab. Quadrant growth 11. Identify the organism growing on the TOP half of the agar and describe the observed hemolytic properties. Staph Aureus; Beta hemolysis is observed based on the zones of clearing within the red agar. 12. Would you expect to see a color change when pseudomonas is streaked onto an EMB agar plate? Explain your answer. No. There would not be a color change because pseudomonas does not ferment lactose. LAB 5 EXAM 1. The Kirby-Bauer method for examining antibiotic sensitivity is also known as what? The Standardized Disc Susceptibility Test 2. True or False. The antibiotic discs are placed onto the LB agar plate before spreading the bacterial culture on the plate. False. The antibiotic discs are place onto the plate AFTER the culture has been spread. 3. When performing the Kirby-Bauer method the areas of clearing surrounding an antibiotic disc after an overnight incubation are known as what? Zones of Inhibition. 1. Why was an LB agar plate used to test the Staph culture as opposed to a selective/differential agar that only grows Staph? LB agar is used as it simply provides the nutritional requirements to encourage bacterial growth. Since the results of the Kirby Bauer method is directly based on bacterial growth patterns, no other selective or differential additives should be present that may hinder or inhibit the samples growth. 2. What unit of measurement is used when determining the size of the zones of inhibition? A. Centimeters B. Micrometer C. Millimeters D. Meters 3. True or False. In order to maintain proper spacing the antibiotic discs should be placed approximately a fingers width from the edge of the plate. True. The disc should be placed approximately a fingers width from the edge so that a uniform zone of inhibition can be seen around the entire disc. 1. Given the following image, determine whether the bacterial sample is resistant or susceptible to the following antibiotics. A—24mm (because radius is given) Susceptible B—9mm Susceptible, despite small zone of inhibition. C—14mm Resistant LAB 6 exam 1. True or False. The presence of cytochrome C is often associated with aerobic bacteria. True 2. Which STD is most often identified using the Oxidase test? Gonorrhea 3. Using the catalase test, a Staphylococcus sample would be: A. Gram (+), Catalase. A. Gram-positive, Catalase-positive. 4. True or False. The catalase test is a qualitative and selective assay. False. The catalase test is a qualitative and differential assay. 1. Fibrin is another term for ? blood clots 2. Once you inoculate the rabbit plasma containing media for the coagulase test, how long do you wait to read the sample results? D. 12-14 hours which is the equivalent of an overnight incubation. 3. How is fibrin beneficial to a bacterium in terms of antibody recognition? The presence of fibrin can form a ‘hard’ shell (or coat) around the bacterium, making antibody binding difficult. If antibodies are unable to bind, the bacterium can escape immune detection. 4. The hydrolysis of triglycerides on a spirit blue agar plate most closely resembles that of hemolysis on a blood agar plate. B. Beta. 5. As stated in the lab video, an example of a lipase-positive bacterium is: C. Bacillus subtilis. An unknown bacterium (Sample A) was tested using several of the rapid, qualitative tests described within this lab lecture. Using the images of the results below indicate the lab results for each test (1-3) as either positive or negative, then using the decision tree identify the unknown bacterium by the corresponding letter. The unknown sample is: Oxidase-positive (aerobic), catalase negative and coagulase- positive, which on the decision tree, corresponds with the letter C.