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Lab Quiz 2
3,4,5,7
Question | Answer |
---|---|
Lab3: What is the minimum number of bacteria present on one of your plates? How do you know? | 1;The minimum number of bacteria will be represented by the number of colonies. |
Lab3: What is the value of the Petri plates in microbiology? | Provides a larger surface area for examination. |
Lab3: What are the bacteria using for nutrients in the nutrient agar? | peptone, beef extract,sodium chloride(NaCl), Agar, Distilled water |
Lab3: What is the purpose of the agar? | The agar is a solidifying agent. |
Lab3: Why is agar preferable to gelatin as a solidifying agent in culture media? | It stays solid in high heat. |
Lab3: Did all the organisms living in or on the environments sampled grow on your nutrient agar? Explain. | Yes, we could see the colonies from the wooden spoon. |
Lab4: Were any of the bacteria growing in the semisolid agar deeps mobile? Explain. | Yes, L.Lactis and Proteus vulgaris. They were spread wider at the top of the deeps. |
Lab4: What is the primary use of slants? | To provide a solid growth surface; easier to store/transport. |
Lab4: What is the primary use of deeps? | used to grow bacteria that requires less O2 than the medium. |
Lab4: What is the primary use of broths? | Provide large numbers of bacteria in a small space - easy to transport. |
Lab4: What is the purpose of flaming the loop before use? After use? | sterilization |
Lab4: Why must the loop be cool before you touch it to a culture? Should you set it down to cool? How do you determine when its cool? | So you don't kill the bacteria; no; wait 30 seconds. |
Lab4: Why is aseptic technique important? | To decrease contamination. |
Lab5: Which bacterium is a rod? | Bacillus subtilis |
Lab5: Which bacterium is larger? | Megaterium |
Lab5: Of what value is a simple stain? | Simple stains can be used to determine cell morphology, size, and arrangement. |
Lab5: What is the purpose of heat-fixing the smear? | It preserves microbes with minimal shrinkage or distortion when stained. Also to kill bacteria and have them stick to the side. |
Lab5: In heat fixing, what would happen if too much heat were applied? | It can "blow up"/ break apart all the microbes and we wouldn't be able to see them. |
Lab7: Which of the bacterial cultures were gram-positive? | Staphylococcus and Baccillus |
Lab7: Which of the bacterial cultures were gram-negative? | Escherichia |
Lab7: Did your results agree with the information in your textbook? If not, why not? | Permeability differences or variability in decolorizing; The age of the gram positive culture would account for differences in the stain. |
Lab7: Why will gram-positive cells more than 24 hours old stain gram-negative? | When bacteria die, their cell walls degrade and may not retain the primary stain. |
Lab7: Can iodine be added before the primary stain in a gram stain? | No, it must be complex with the primary stain. |
Lab7: Which step is omitted without affecting determination of the Gram reaction? | Safranin |
Suppose you performed a Gram stain on a sample from a pure culture of bacteria and observed a field of red and purple cocci. Adjacent cells were not always the same color. What do you conclude? | The bacteria are gram positive. The culture was old, and some of the cells had lost their ability to retain the dye. |
Lab7: Suppose you are viewing a Gram-stained field of red rods and purple cocci through the microscope. What do you conclude? | This is a mixed culture. |
Lab7: Considering you can't identify bacteria from a Gram stain, why might a physician perform a Gram stain on a sample before prescribing an antibiotic? | Antibiotic sensitivity (eg penicillin) correlates with wall type (Gram reaction). |
Lab7: If you performed a Gram stain on human cells, what would happen? | Human cells don't have cell walls. The primary stain would be easily removed with alcohol. |
Chemically defined medium | A medium whose exact chemical composition is known. |
Complex Media | Media for which the exact chemical composition varies slightly from batch to batch. |
Nutrient Broth | Commonly used liquid complex medium. |
Nutrient agar | When agar is added to a nutrient broth, it becomes a solid medium. |
Agar | an extract from marine red algae, had some unique properties that make it useful in culture media. |
Steam Sterilization(Autoclave) | the most common method of sterilizing culture media- uses steam under pressure. Heated at 121 deg Celsius@15 lbs of pressure(psi) for 15 minutes. |
Petri plates | Contains a solid media and provides a large surface area for examination of colonies. |
Inoculated | Intentionally introduced onto nutrient agar and into nutrient broth. |
Incubation period | Keeping bacteria in an appropriate temperature to help it grow. The bacteria that are inoculated into the culture media increase in number. |
Turbid | A result of bacterial growth, liquid media becomes cloudy. |
Colony | A population of cells that arises from a single bacterial cell. |
Colony Forming Unit | (CFU) A colony may arise from a group of the same microbes attached to one another. |
Contaminants | Unwanted microbes |
Aseptic Technique | Refers to a procedure that is performed under sterile conditions. This includes medical and laboratory techniques, such as with microbiological cultures. It includes techniques like flame sterilization. |
Sterilized | Rendered free from all life, prior to use. |
Broth Cultures | Provide large numbers of bacteria in a small place and are easy to transport. |
Agar Slants | Test tubes containing solid culture media that were left at an angle while the agar solidified. |
Agar Deep | Agar solidified at the bottom of a test tube. Used to grow bacteria that require less oxygen than is present on the surface of the medium. |
Inoculating loop | Aseptic transfer and inoculation are usually performed with a sterile, heat-resistant, non-corroding Nichrome wire attached to an insulated handle. End of wire is bent into a loop. |
Inoculating needle | Aseptic transfer and inoculation are usually performed with a sterile, heat-resistant, non-corroding Nichrome wire attached to an insulated handle. The wire is straight. |
Fixed | To kill bacteria or stick them to a slide. |
Chemically fix | Cover smear with 95% methanol for 1 minute. |
Chromophore | The ion that is colored. |
Basic Stain | If the chromophore is a positive ion. |
Acidic Stain | If the chromophore is a negative stain. |
Direct Stain | A simple stain that stains the bacteria. |
Negative Stain | A simple stain that stains the background. |
Gram Stain | Crystal Violet, Iodine, Alcohol, Safranin. Allows you to classify bacteria as Gram + and Gram- |
Gram Negative | Bacteria that decolorize easily. Alcohol leaves holes in Peptidoglycan and Crystal violet washes out. |
Gram Positive | Bacteria that retain the primary stain. Alcohol dehydrates the cell wall and crystal violet- Iodine cannot leave the cell. |