Synthroid Online

posted on 27 Aug 2012 06:42 by synthroidonliney
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solid agar (meat extract 0.3 per cent, peptone 0.5 per cent, agar 0.5 per cent). Motile organisms show a diffuse zone of growth spreading from the line of inoculation; nonmotile cultures do not. For this test, incuba- tion should be for 6 days at 30 C Unless positive results are secured sooner. For gram-negative nonsporeformers, 12- to 18-hr incubation gives Synthroid Online more clear-cut results. This test is a good check on the hanging-drop method but is slow and requires some experience before one can be certain how to interpret results. The medium can now be obtained in dehydrated form under the name Motility Test Medium. Conn and Wolfe (1938), moreover, have recommended a flagella stain even on cultures that do not appear motile upon examination in hanging drop. The modification of the Synthroid Online Bailey flagella stain given in Chap. II is simple and quick enough to be employed for routine examinations; posi- tive results cannot be misinterpreted and show the arrangement of flagella as well as the mere presence or absence of motility. A few further refine- ments of the method, making it more adaptable to routine use on bacteria of various Synthroid Online types, published by Fisher and Conn (1942), are also given in Chap. II. The Leifson (1951) procedure is also well suited for routine use. ROUTINE TESTS FOR THE IDENTIFICATION OF BACTERIA 151 Presence of endospores. Routine examinations should be made on agar slant cultures a week old, employing methylene blue or dilute crystal violet to stain the vegetative rods and leave spores unstained. If spore- hke bodies are present whose exact nature is uncertain, one of the spore stains recommended in Chap. II should be employed. In most cases there is little trouble in finding spores if the organism pro- duces them. All rather large rods, however (0.8 y, or more in diameter) , should be regarded as possible spore producers even if microscopic examination does not show spores. Such bacteria should be mixed with sterile broth or physiological saline solution and heated to 85C for Synthroid Online 10 min ; if still alive, endospores may be regarded as probably present. One should also make repeated transfers of the culture onto agar and examine at various ages. A culture of a large rod should not be recorded as a nonsporeformer unless all these tests are negative. Acid-fast staining. Various methods have been proposed for determin- ing if an organism is ''acid fast." They are all essentially modifications of the same general procedure and are similar to the spore stains of Moeller (1891) and Foth (1892). The committee is as yet unprepared to recommend any one of them in particular. Several are listed in Chap. II. Capsules. An organism should not be recorded as having capsules unless they have been actually stained by one of the methods of capsule staining described in bacteriological textbooks. Four of the common methods of Synthroid Online capsule staining, namely those of Anthonj^, of Hiss, of Huntoon, and of Churchman, are given in Chap. II. The committee has obtained good results with Anthony's and Hiss' methods. Capsules do not appear in all media ; the medium of choice should be milk serum slants or exudates from infected animals. Irregular forms. Forms that differ from the typical shape for the organism, such as branching forms, clubs, spindles, or filaments, should be noted and sketched. Simple observation is enough to show that these irregular forms occur quite uniformly in certain cultures; hence their existence must not be ignored. The Synthroid Online interpretation of these forms is at present under dispute, and the decision as to their significance must be awaited. The committee recommends that the microscopic study of any culture include an examination of the growth on various media and at various ages upon each medium, mth sketches of all the shapes that occur. Gram stain. The gram stain was until recently an entirely empirical procedure for distinguishing between two groups of organisms, the actual significance of which was not understood. Since 1940, however, the work of Henry and Stacey (1943), Bartholomew Synthroid Online and Umbreit (1944), and others has shown that a positive reaction is dependent upon the presence of ribonucleic acid in the outer layers of the cells, which can be removed by treatment with ribonuclease and replated on them by treatment with 152 Synthroid Online MANUAL OF MICROBIOLOGICAL METHODS magnesium ribonucleate. Thus gram-positive organisms can be arti- ficially converted to gram-negative ones and then restored to their gram- positive state. In addition to this fact, it is also true that many bacteria are neither definitely positive nor negative; some organisms are gram-variable and may appear either negative or positive according to conditions. Other organisms contain granules which resist decolorization and may cause Synthroid Online misinterpretation. The importance of taking such variations into account has been repeatedly emphasized. Such organisms should be recorded as gram-variable rather than made to appear either positive or negative by some modification of technic. To determine if an organism belongs to this variable group, it is necessary that it be stained at two or three different ages by more than one procedure. If an organism changes from positive to negative or Synthroid Online vice versa during its life history, this change should be recorded, with a statement as to the age of the culture when the change was first observed. It is often practical to record such an organ- ism as prevailingly positive or prevailingly negative ; obviously, however, this cannot be done without a very considerable series of determinations. Tests must therefore be made after 1 and 2 days' incubation, sometimes also in even older cultures. It must, moreover, be recognized that gram- variahle organisms are not necessarily ones that show uneven gram stain- ing; the latter should be recorded as staining unevenly, not as gram- variable. The two methods at present recommended are the ammonium oxalate method (Hucker) and Kopeloff and Beerman's modification of the Burke technic. In the former the manipulation is more simple, but the latter gives better results if the organism is growing in a medium that may be of acid reaction (e.g., exudates) and is claimed to distinguish better between true and false positive reactions. These two procedures are given in Chap. II. RELATION TO FREE OXYGEN In relation to free oxygen, organisms are generally classified as strict aerobes, facultative anaerobes, or strict anaerobes. A fourth group of microaerophiles may also be recognized. None of these distinctions is clear cut, but the following method gives a rough grouping of bacteria in regard to their oxygen requirements. Agar shake culture affords a good routine method of determining the oxygen requirements of an organism. A tube of deep agar medium con- taining glucose or some Synthroid Online other available carbon source is inoculated while in fluid condition at 45C with an inoculum not too heavy to permit dis- crete colonies, rotated to mix the inoculum with the medium, and cooled.
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