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Lab Quiz 2 Review
Lab Ex.'s 3,4,5,7
| Question | Answer |
|---|---|
| What is a smear? | To stain bacteria, a thin film of bacterial cells must be placed on a slide to be viewed through a microscope. |
| Fixing | Denatures bacterial enzymes, preventing them from digesting cell parts, which causes the cell to break(autolysis). |
| Heat fixing | A slide is run through a Bunsen burner flame several times to dry the smear, does not kill the bacteria. |
| Chemically fix | Cover the smear (with bacteria on it) with 95% methanol for 1 minute. |
| What is a chromophore? | The ion that is colored. If chromophone is a (+) ion like methylene blue , the stain is considered a basic stain; if it is a (-) ion it is an acidic stain. |
| Simple stain | Staining procedures that use only one stain. Can be used to determine cell morphology, size, and arrangement. |
| Direct stain | A simple stain that stains the bacteria. |
| Negative stain | A simple stain that stains the background but leaves the bacteria unstained. |
| Of what value is a simple stain? | quick observation of the morphology and arrangement of bacteria. |
| What is the purpose of heat fixing the smear? | To makes the bacteria sticky so they stick to the slide. |
| In heat fixing, what would happen if too much heat were applied? | It would burn and/or kill the bacteria. Cells would be completely destroyed "plasmylosis" and burst and bacteria would not hold stain. |
| What bacterium is a rod? | Baccillus |
| Which bacterium is larger? | B. megaterium |
| Gram stain | A differential stain that allows you to identify and classify bacteria as either gram- positive (+) or gram-negative (-). |
| Primary stain (1st step in gram staining) | Crystal Violet (basic dye stains bacteria purple). |
| Mordant (2nd step in gram staining) | Gram's Iodine (combines with crystal violet in cell to from a crystal violet-iodine complex (CV-I)). |
| Decolorizing agent | Ethanol of ethanol-acetone (primary stain is washed out (decolorized) of some bacteria, whereas others are unaffected. |
| Secondary Stain or Counter Stain | Safranin (a basic dye which stains the decolorized bacteria red). |
| Gram-negative(-) | Those that decolorized easily |
| Gram-positive(+) | Those that decolorize slowly and retain the primary stain. |
| Peptidoglycans | Bacteria cell walls are composed of this complex lattice structure along with other compounds. Gram(+) cell walls contain multiple layers of peptidoglycans, whereas gram(-) bacteria contain a thin layer of peptidoglycan. |
| Why will gram (+) cells more than 24 hours old stain gram (-)? | They may be old cells that have a deteriorated cell wall, as cell age there cell walls degrade which may nor allow bacteria to retain stain and give inaccurate results. |
| Can iodine be added before the primary stain (crystal violet) in a Gram stain? | No |
| Suppose you performed a Gram stain on a sample from a pure culture of bacteria & observed a field of red and purple cocci. Adjacent cells were not always the same color. What do you conclude? | That some were a successful stain & the others may have been dead or just didn't retain the stain. |
| Suppose you are viewing a Gram-stained field of red rods and purple cocci through the microscope. What do you conclude? | A mixed culture OR contamination has occurred. |
| 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 correlates with the cell wall type of the bacteria. |
| If you performed a Gram stain on human cells, what would happen? | NO cell walls, the cells would not hold the stain, ETOH (alcohol) would destroy the membranes (phospholipid bilayer). |
| Chemically defined medium | A medium whose exact chemical composition is known. |
| Complex media | Media for which the exact chemical composition varies from batch to batch. |
| Nutrient broth | Is a commonly used liquid complex medium. |
| Nutrient agar | When agar is added to the nutrient broth it becomes a solid medium. |
| Agar | An extract from marine red algae, has some unique properties that make it useful in culture media. Few microbes can degrade agar, so it remains solid during microbial growth. |
| Steam sterilization OR autoclaving | Which uses steam under pressure( during this process, material to be sterilized is placed in auto-clave and heated to 120 C at 15 lbs. of pressure for 15 minutes. It's the most common method of sterilizing culture media that are heat stable. |
| Petri plates | Contain solid media which provide a large surface area for examination of colonies. |
| Inoculated | Intentionally introduced, into various forms of culture media to keep them alive and to study their growth-without introducing unwanted microbes. |
| Incubation period | Bacteria that are inoculated into culture media increase in number during this period. A period of usually 24-48 hours were bacteria are heated a 98.6 degrees Fahrenheit to allow microbial growth. |
| Turbid | After a suitable incubation, liquid media become cloudy as a result of bacterial growth. |
| Colony | A population of cells that arise from a single bacterial cell. |
| Colony-forming unit | When a colony arises from a group of the same microbes attached to one another. |
| What is the minimum number of different bacteria present on one of your plates? How do you know? | > or equal to 1. > or equal to 1 colony type seen. |
| What is the value of Petri plates in microbiology? | Have a larger surface area, easier to subculture so that you can see the isolated colonies of bacteria. |
| What are bacteria using for nutrients in the nutrient agar? | Peptones and beef extract |
| What is the purpose of the agar? | A solidifying agent ( solid/semi-solid surface to grow bacteria). |
| Why is agar preferable to gelatin as a solidifying agent in culture media? | It stays solid at incubator temp of 98.6 degrees Fahrenheit and most bacteria can't eat or digest it. |
| Did all the organisms living in or on the environments sampled grow on your nutrient agar? | No Way! We only provided one food type and one growing temperature. |
| Contaminants | Unwanted microbes |
| Aseptic technique | Used in microbiology to exclude contaminants and is performed under sterile conditions. |
| Sterilized | Rendered free of all life, prior to use, usually accomplished during autoclave. |
| Broth cultures | Provide large numbers of bacteria in a small space and are easily transported. |
| Agar slants | Test tubes containing solid culture media that were left at an angle while the agar solidified. Provide solid growth surface but are easier to store and transport than Petri plates. |
| Inoculating loop and Inoculating needle | When end of wire is bent into a loop AND when it's straight.(Aseptic transfer and inoculation are usually performed with this sterile, heat-resistant, noncorroding Nichrome wire attached to an insulated handle). |
| Agar deep | Solidifies at the bottom of the test tube, often used to grow bacteria that require less oxygen than is present on the surface of the medium. |
| Were any of the bacteria growing in the semisolid agar deeps motile? | Yes, resembled an upside down Christmas/pine tree. (Motile bacteria will move away from the point of inoculation, giving the appearance of an inverted pine tree) |
| What is the primary use of slants? | Solid surface,easier to store than plates and not easily contaminated. |
| What is the primary use of deeps? | Motility and oxygen requirements. |
| What is the primary use of broths? | To maximize growth (the rate/amount) |
| What is the purpose of flaming the inoculating loop before use? After use? | Before for sterilization to minimize contaminants. After for the safety of people within the lab. |
| Why must the loop be cool before you touch it to a culture? Should you set it down to let it cool? | So you don;t burn and or kill the bacteria your trying to obtain. No because you risk contaminating it again and will have to re-heat the loop, always keep in your hands when in use. |
| Why is aseptic technique important? | It minimizes the transfer of bacteria and contaminants from one thing to another. |
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KJones040607
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