Laboratory Methods Part G: Methods and Materials Laboratory Methods A. Sterile Techniques Sterile technique is always a relative matter. ![]() Serial Vs Parallel Dilutions. Devices connected directly to a phone socket pass. Subsequent dilution of the first sample in a serial dilution method may. The numbers of prokaryotes in a sample can be expressed in two ways: the total count or the viable count. Flow cytometry is a method, similar in concept, in which the number of particles in a. The dilution factor chosen for the series of calibration standards is achievable by using serial dilution. The progression of calibration standard concentration is always a geometric series. The precautions required depend on the experimental situation, including the growth media used, the competitive abilities of the experimental organism, the duration of the experiment, and the intended use of the culture. For these experiments the most serious contamination problem is mold. Many common molds grow well on yeast media and compete effectively, over-growing the plates and obscuring those yeast that do manage to grow. Bacteria are less of a problem as most of them do not grow well on these media and, with a little experience, one can easily distinguish them from yeast. Other strains of yeast can be disastrous contaminants if they go undetected. In particular, a red yeast that sometimes shows up can be really confusing, but is distinguished from our red yeast because it doesn't require adenine. In contrast to short-term experiments, however, sterilizing media must be quite rigorous because storage allows ample time for even slow-growing contaminants to develop. We have concluded from experience that storing media in the cold is actually counter-productive. It does not prevent contamination, but slows its growth. Consequently contamination may go undetected until the cultures are incubated. It is much better to store media at room temperature and detect contamination before the medium is used. (1) Sterilizing With Moist Heat Moist heat provided by an autoclave or pressure cooker is an efficient way to sterilize most materials. At a pressure of 15 psi above atmospheric pressure, water reaches a temperature of approximately 121O C before it boils. Most materials are effectively sterilized by 15 minutes exposure to this temperature. If an autoclave is not available, an ordinary household pressure cooker will effectively sterilize media supplies in small batches. (2) Sterilizing With Dry Heat Dry materials such as glass and metal may be sterilized in an oven, but this requires higher temperature (160O C) and longer time (at least 2 hours) than an autoclave. This is most practical for glassware when an oven controlled by an automatic timer is available so that sterilization and cooling can occur overnight. Use of disposable, pre-sterilized, plastic ware makes the oven less important. (3) Sterilizing by Flaming The flame from a gas burner effectively sterilizes small glass or metal objects, such as inoculating loops, but one must avoid 'frying' the yeast by contact with objects heated in a flame. Dip glass spreaders in alcohol and then use the flame to ignite the alcohol. Place metal tools such as loops in the flame until they are red hot. Cool hot tools by touching them to the agar or inside of a sterile glass tube. However, since flames are dangerous this method can and should be avoided whenever possible. We have found that flaming is really only necessary to sterilize inoculating loops and small instruments. Zippyshare.com is completely free, reliable and popular way to store files online. We offer fast download speeds. The maximum filesize for a single file is 500 MB. Free download Bel Biv Devoe – That Girl Is Poison Mp3. We have about 21 mp3 files ready to play and download. 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(4) Sterilizing With Alcohol In many experimental procedures, the most effective way to sterilize objects is with ethanol. Either 95% or 70% will work. The latter is actually more effective, but the former is often more convenient. Of course the alcohol must be allowed to evaporate or be burned off before the object is used in contact with the yeast. Use a flame to burn off the alcohol, a candle is generally less expensive and safer than a gas burner. The alcohol, more than the heat, does the sterilizing, so just 'light' the alcohol to minimize heating and speed up the process.
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