10/28/2023 0 Comments Diagrams of bacteria shapes rod shapedThese cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. Principles of Inheritance and Variation.New Questions and Answers and Forum Categories The polarly flagellated bacteria are gram negative. All spore- producing bacteria are gram-positive. The division of bacteria into gram-positive and gram-negative forms, on the basis of the reaction to gram-stain, is correlated with other characterisic differences between them. It gives a good colour to the gram-negative bacteria and at the same time contrast with the purple of the gram-positive bacteria. To study their details the final step in the staining procedure is to apply the counter stain such as eosine or safranine to the smear. The decolourised bacteria (gram-negative) are nearly invisible. Those which yield it to the solvent (alcohol) and become decolourised are called gram-negative. The bacteria that keep the original purple stain are called gram-positive. The next step in the staining procedure is to apply and renew 95 percent ethyl alcohol to the smear until all except the thickest layers of the smear have ceased to give off the dye.Įxamination of the smear at this stage reveals that many of the bacteria still retain the original purple colour whereas from others it has been washed off. The iodine solution, in turn, is rinsed off the smear after 30 seconds.Įxamination of the smear with the microscope reveals that all the bacteria have taken the purple colour. The smear is next with an aqueous solution of iodine which is prepared by adding 1.0 gm Iodine and 2 to 5 gm potassium iodine to 300 ml of distilled water.īefore use the solution is allowed to stand for 24 hours for iodine to dissolve. The dye is applied for 30 seconds to the bacterial smear. The dye is prepared by dissolving 2.0 gm of Crystal violet (80% dye content) in 20 ml of Ethyl alcohal (95%). The procedure involves the staining of a bacterial smear containing a variety of bacteria with crystal violet solution. Gram, in 1884 and thus named, the Gram stain after its discoverer. It was devised by the Danish bacteriologist. It is a differential stain which has a simple staining procedure. The most important and commonly used of bacterial stains is the Gram stain. In a few species, however, several types of cell forms may occur in the life cycle.įor example, Acetobactor, a group of vinegar bacteria occur as small rods, long rods, ellipsoids or a chain of small rods. Some bacteria are able to change shape and size with changes in the environmental conditions. Granules of sulphur accumulate within the cells. A group of filamentous forms including Beggiatoa and Thiothrix oxidize hydrogen sulphide. The number of filamentous forms, as compared with others, is very small. Vibrio comma is a typical example of this category.Ī fourth type of form may occur in a few species. The vibrios have flagella at one pole only and seldom exceed 10µ in length and 1.5 to 1.7µ in diameter. In fact it is less than the full turn of a helix and shaped much like a slightly twisted comma. The bacterium cell in the vibrios is short and looks like a curved rod (I) or twine of a spiral. volutans are the common examples of this type. They occur as single cells or in short chains but do not form colonies. The spirilla forms usually bear two or more flagella at one or both poles. They are smaller in number probably with fewer than 100 species. The Spirilla are larger than the cocci and bacilli ranging form 10-50µ in length though only 0.5µ to 3µ in diameter. The bacteria having the body twisted spirally like a cork-screw through 1-5 complete turns are the Spirilla (sing. The helical forms are of two types, spirilla and vibrios. the spherical cells divide regularly in three planes producing box-like cubical packets of eight or multiples of eight with the cells arranged in rows (G). The coccal cells form loose masses of variable size and irregular in shape like bunches of grapes (H) in Staphylococcus (S.
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