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Lab Quiz 2


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.
Created by: Lproctor