Microbiology Lab Exam 3 Actual Exam Questions With Correct Answers.

What is a pure culture? A mixed culture? Which occur in nature? - correct answers Pure = Only 1 species Mixed = Multiple species Mixed occurs in nature Know the cell: colony ratio. If you count 500 colonies on your Petri plate, how many cells was the media inoculated with? - correct answers1 Colony = 1 Cell 500 Colonies = 500 Cells What is the purpose of performing the radiant streak? - correct answers To isolate singular colonies via disbursement Why are tubes of media cooled to 50◦C? What will happen if the tubes are inoculated at higher temperatures? What happens to the media if it is allowed to cool below 50◦C? - correct answers Cooled to 50 so that the media remains liquid and you don't kill the cells. How is isolation of cells achieved in the pour plate method and the radiant streak method? - correct answers Pour Plate - the cells are suspended in the media (dilution) Radiant Streak - cells are spread via inoculating loop At what temperature does agar solidify? - correct answers42*C What was the most common temperature used to incubate bacteria? - correct answers36*C Large, circular colonies growing on the surface of the media indicate what type of oxygen use by the bacteria? Small, elliptical colonies growing below the surface of the media indicate what type of oxygen use by the bacteria? - correct answers Surface = Aerobic Below = Anaerobic Why do we incubate petri plates upside down? - correct answers To avoid having condensation on the surface of the agar Media enriched with a 7.5% NaCl solution would promote the growth of what type of microorganisms? Give on specific type of bacteria grown on this type of media. - correct answersHalophiles Staph Aureus What type of media was used to cultivate fungus? Bacteria? Why are these media used to cultivate bacteria? - correct answersFungi - Sabourad's Agar Bacteria - Nutrient Agar How does incubation temperature relate to food storage? - correct answersWhen foods are heated to TDP prior to storage, bacterial growth is minimal (except for spores). Keeping foods at lower temperatures also prevents bacterial growth. Why do you leave the tubes of broth at the various temperatures for 15 minutes before inoculating them? - correct answersTo make sure the temperature is met throughout the medium and is consistent. Given data in chart form, be able to determine the following information: thermal death point for an organism, and explain why certain organisms have no thermal death point in the temperature range represented. - correct answersTDP = temperature at which cells die No TDP = spore forming bacteria What is the purpose of using the swab technique to inoculate a petri plate? - correct answersIt provides for complete coverage Given data in chart form, be able to determine the following information: optimum NaCl and sugar concentration for growth of bacteria and fungi. - correct answers What generally happens when NaCl concentration increases? If the organism can grow at a high NaCl concentration then it is classified as a --------. List a specific type of bacteria that fits this description. - correct answersHalophiles will flourish - Halophiles LOVE NaCl Staph Aureus Does an increase in the sugar concentration have the same effect on the growth of bacteria and fungi compared to an increase in NaCl concentration? Why or why not? - correct answersBacteria do not flourish with high sugar but Fungi do. Some bacteria flourish in high NaCl (halophiles), fungi do not. Fungi use sugar as an energy source, some bacteria like the decreased water activity provided by high salt concentrations. If growth is inhibited by different NaCl and sugar concentrations, what happens to the cells to cause their death? - correct answersThe water activity is not desirable and the cells lyse List the factors /variables that influence the effectiveness of UV light as an antimicrobial and what impact do they have on microbe growth. - correct answers1. Type of Microbe (spores are resistant to UV) 2. UV wavelength (is it strong enough to disrupt cell walls/membranes?) 3. Length of exposure 4. Direct or indirect exposure 5. Distance from source What is the purpose of covering ½ of the petri plate with cardboard? - correct answersTo prevent exposure to the UV light What accounted for the growth seen on the petri plate containing Bacillus subtilis after UV exposure? - correct answersBacillus are spore formers - UV light does not kill spores What type of cells are killed upon exposure to UV light? - correct answersLiving cells (not spores) What accounts for the growth on the petri plate where the lid was left on, and not covered by cardboard? How does this result relate to the use of UV light as a sterilizing agent for packaged food? What is a better option for sterilizing packaged food? - correct answersThe UV light does not penetrate the plastic cover and therefore will not kill the bacteria. Ionizing/Gamma radiation works better for food. List the factors that influence the effectiveness of chemical agents used as disinfectants and what impact they have on microbe growth. - correct answers- exposure time - Mechanism of agent - type of microbe - concentration of agent Why is it important to flame the forceps between each use when using different bacteria contaminated pins? - correct answersTo make sure that they are sterile and that you are getting true results from the pin's exposure to a disinfectant What 3 things would you look for to determine if bacteria were growing in a liquid medium? - correct answersTurbidity Sediment Pellicle Why is it important to achieve complete coverage of the agar surface with the microbe when using the swab technique in this exercise? (Antibiotic Eval) - correct answersTo get a clear representation of whether or not bacteria are able to grow near the discs. Why is it important to flame the forceps between each use when applying the antibiotic disc to the agar surface? - correct answersTo avoid cross-contamination What does a clear ring around an antibiotic disc indicate? What does the wideness of the ring indicate compared to smaller rings? What does no ring around the antibiotic disc indicate? - correct answersRing = zone of inhibition Wider - more effective Smaller - less effective No ring - no effect How does the antibiotic saturated disc get into the medium of the petri plate? - correct answersYou press it slightly Given data in chart form, be able to determine the following information: is the antibiotic effective or not effective at inhibiting microbe growth, is the agent antibacterial or antifungal, is the agent narrow spectrum or broad spectrum. - correct answersLOOK AT LAB CHART Describe the aseptic technique and why is it important. - correct answersFlame all components when possible and limit exposure to air. This prevents contamination. What is the color of phenol red before inoculation and incubation? What compounds are added to the phenol red broth? What biochemical reaction does phenol red indicate for each of the compounds that were added to the tubes? How do you know if this reaction occurred? - correct answers- Red -Glucose, Sucrose, Lactose - Yellow = + - Red = - - Indicates fermentation, bubbles indicate CO2 production What compound was added to the MR-VP broth? What is the initial color of the methyl red indicator? What biochemical reaction does the methyl red test for? What indicates a positive or negative result? If the result is positive, what is the organism able to do, and what end products are produced? - correct answers-Glucose - Methyl Red = Red -Test for Fermentation - Red = Positive - Yellow/orange = Negative -Positive = microbe is able to ferment glucose and produce acid What biochemical reaction does Barritt's reagent test for? What is the name of this test? What indicates a positive or negative result? If the result is positive, what is the organism able to do? - correct answers- Aerobic Oxidation - Aerobic Respiration - Positive = Medium pink - Negative = NOT pink - Indicates alcohol production Can an organism test positive for both Barrit's and MR-VP? - correct answersYes. What is the purpose of catalase? What reagent is used to detect the presence of this enzyme? If catalase is present, what indicates a positive reaction? Does this test indicate that the organism is aerobic or anaerobic? - correct answers- Does the microbe posses the enzymes to process O2 - H2O2 (Hydrogen Peroxide) - Bubbles form = Positive - No Bubbles = Negative - Yes. If positive = aerobic, negative = anaerobic What is the purpose of oxidase? If oxidase is present, what color will the organism turn? Does this test indicate that the organism is aerobic or anaerobic? - correct answers- O2 Processing - Positive = Purple - Purple = aerobic Why was the triple sugar iron tube inoculated using the stab technique? - correct answersTo determine if bacteria produced H2S gas Why was the Simmons citrate tube inoculated with streak method and the stab method? - correct answersTo determine if bacteria were acid producers (oxidation) What is hydrolysis? - correct answersThe splitting of macromolecules into smaller molecules by the addition of H2O in the presence of appropriate enzymes What indicator is used to detect oxidation in the Simmons citrate agar? What indicates a positive or negative reaction? Is this an indication of aerobic or anaerobic respiration? - correct answers- Indicator = Brom Thymol Blue - Positive = Medium Blue