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Microbio Lab Final
| Question | Answer |
|---|---|
| How do most bacteria that achieve motility do so? | The long, slender, whiplike appendages called flagella |
| Describe a positive motility test employing SIM agar | Cells move outward from the stab to establish a broad zone of growth. Also, adding Kovac's reagent to the tube will turn the liquid from green to pink |
| Describe a negative motility test employing SIM agar | A non-motile strain strain which establishes a very narrow zone of growth. Kovac's reagent does not change color |
| When suing SIM agar, why may a bacterium appear to be motile when it really isn't | A two-dimensional pattern will indicate a slash stab. |
| How can you differentiate between true motility and "slashed stabs" in SIM agar? | Positive motility with have a broad zone of growth/ Hold tube up to light to see if there is a two-dimensional pattern (slashed stab) or not |
| Describe directional motion of bacteria | Flagella moves bacteria in one direction for a few moments |
| Describe Brownian movement | Random, vibrational movement which increases with temperature of the medium/ submicroscopic particles collide with the visible objects |
| Describe the procedure for preparing a hanging-drop slide | Applu petroleum jelly to edges of coverslip/ two loops of water to the center. Asceptically transfer small portion of bacteria to the water & mix/ Invert and place depression slide on the coverslip with the drop of broth in the depression/ Quickly invert |
| List at least 5 types of biochemical tests used in the identification of microbes: | Catalase/ Indole/ Citrate/ TSI/ MR Test |
| Describe two ways in which biochemical tests are used to identify microorganisms: | Testing reagents: allows to find the presence or absence of certain enzymes/ Streaking PEA and EMB plates to determine Gram (+) and GRAM (-) bacteria |
| What type of medium is specially formulated to allow the growth of certain species while inhibiting growth of other species? | Selective Media (PEA) |
| What type of media contain pH indicators that differentiate between microbes that utilize a particular chemical and those that grow but do not utilize the chemical? | Differential Media (EMB) |
| Explain why Phenylethyl alcohol agar (PEA) and eosin-methylene blue agar (EMB) are considered selective media: | PEA allows growth of Gram (+) microbes/ EMB selects for Gram (-) rods/ Some microbes grow well on both PEA and EMB |
| What type of organisms are allowed to grow on PEA agar? EMB agar? | Staphylococcus aureus, Streptococcus sp, Clostridium perfringens// E coli, Proteus vulgaris |
| What type of organisms are inhibited by PEA agar? | Aerobic or facultative Gram (-) contaminants |
| Explain why EMB agar is also considered a differential medium: | Used to demonstrate lactose fermentation by Gram (-) rods |
| Describe the appearance of lactose fermenters on an EMB plate | Grows as lavender colonies and develop dark purple centers (nucleated) |
| Describe the appearance of organisms that do not ferment lactose | Pale, non-nucleated lavender colonies |
| Describe the appearance of colonies of E coli on EMB agar | Appear blue-purple, usually with a green metallic sheen |
| List the biochemical tests of the IMViC series: | Indole test/ MR test/ Vogues-Proskauer test/ Citrate-utilization test |
| What two organisms are differentiated using the IMViC series? | E coli & Enterobacter aerogenes |
| Bacteria such as E coli have the ability to remove indole from what amino acid? | Tryptophan |
| The presence of indole following the incubation of a SIM (Sulfur-Indole-Motility) deep is detected by adding a few drops of what reagent? | Kovac's reagent |
| Describe a positive SIM indole test and a negative SIM indole test | Positive= bright red ring at surface of SIM tube/ Negative= color remains yellow |
| Contrast the products of glucose fermentation of E.coli and Enterobacter aerogenes: | E coli produces various acids/ Enterobacter exhibits only limited acid production |
| What indicator is added to MR-VP broth to detect a shift in pH? | Several drops of MR dye |
| Describe a positive MR test, a negative test, and intermediate results | Positive=red/ Negative=yellow/ Intermediate= orange to orange-red// 48hrs of incubation needed |
| What substance is produced by Enterobacter following the metabolism of glucose? How is it detected? | Acetoin / By adding alpha naphthol and potassium hydroxide to the culture |
| Describe a positive VP test and a negative VP test: | Positive=red/ Negative= yellow to brown tube |
| Is Simmon's citrate agar a selective and/or differential medium? | Selective |
| What pH indicator is included in Simmon's citrate agar? | Bromthymol blue |
| Describe a positive Citrate test and a negative citrate test: | Positive=blue/ Negative=green |
| Is E coli capable of utilizing citrate as a source of carbon? Enterobacter? | Enterobacter is capable |
| What is catalase? What organisms produce it? | An enzyme that degrades hydrogen peroxide to form water and hydrogen/ Aerobic microbes |
| Explain why microbes that do not produce catalase must remain in an oxygen free environment: | There would be too much toxic substance: Hydrogen peroxide |
| Describe a positive catalase test and a negative test | Positive= produce bubbles when introduced to hydrogen peroxide/ Negative=no bubbles |
| What three sugars are included in TSI agar? | Glucose/ Lactose/ Sucrose |
| What is produced by members of the Enterobacteriaceae family following the utilization of sodium thiosulfate? | Hydrogen sulfide |
| Describe the procedure for inoculation of a TSI slant: | Streak the surface of the slant and stab deep into the tube |
| Describe the possible results of TSI slants | No sugars fermented: red slant and red butt/ Glucose fermentation only: red slant, yellow butt/ Lactose & glucose fermentation: yellow tube/ Hydrogen sulfide gas production: red slant, black precipitate, yellow butt |
| Describe the procedure for conducting a catalase test: | Place drop of hydrogen peroxide on a clean slide/ use loop to transfer a colony of bacteria from a slant to the hydrogen peroxide drop/ observe for bubbles |
| What types of media can reinforce the results of Gram staining? | PEA and EMB plates |
Created by:
Clinton Perdue
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