When done on cultures less than 24 hours old The decolorizing agent dissolves the outer lipopolysaccharide layer, and the CV-I washes out through the thin layer of peptidoglycan. Iodine reacts with the dye in the cytoplasm to form CV-I. In a gram stain, what type of cell does this describe?Ĭrystal violet is picked up by the cell. Why do bacteria stain differently in a gram stain?Ĭhemical and physical differences in their cell walls In a gram stain, what are bacteria called when they retain the primary stain? In a gram stain, what are bacteria called when they are easily decolorized? What kind of stain is the gram stain? How does is allow you to classify bacteria?ĭifferential as either gram positive or gram negativeĭescribe the discovery of the gram stain technique.ĭiscovered accidentally by Hans Christian Gram in 1884 when he attempted to stain cells and found that some lost their color when the excess stain was washed off What type of dye is used for negative staining? (Acidic or Basic) The lack of heat fixing or strong chemicals keeps from distorting the cellĬould any dye be used in place of nigrosin in a negative stain? Why is the size more accurate in a negative stain than in a simple stain? It's clearer because only the background is stained How does bacteria from a negative stain differ from that of a simple stain? List the steps of the negative staining technique.ġ-Place a drop of nigrosin on slide, 2-Mix a loopful of broth culture with the nigrosin (no extra water is needed when the culture is taken from solid media as nigrosin contains a lot of water already), 3-Use a second slide to sweep the mixture across the first slide, making a color gradient, 4-Let the smear air dry When other staining techniques don't clearly show cell morphology or size When is the negative stain technique especially useful? Negative stain to keep the bacteria from getting as distorted In which procedure are no heat fixing or strong chemicals used and why not? The bacteria cell wall and the chromophores of the acidic stain both have negative charges. Why doesn't a negative stain stain the bacteria? What does the negative stain technique stain?īackground (the area around the cell, but NOT the cell itself) Yes any positively charged dye can be used such as safranin and basic fuchsinīacteria can be seen without staining, so why is fixing and staining important for microbiology? It would damage the cell's structure and can even crack the slide.Ĭan dyes other than methylene blue be used for direct staining? In heat fixing, what would happen if too much heat were applied? What is the purpose of fixing the smear preparation? List the steps of preparing a simple stain.ġ-Cover smear with methylene blue for 30 seconds, 2-Wash with DI waterĭetermining cell morphology, size, and arrangement Staining procedures that use only one stainġ-Place a loopful on water on the slide, 2-place a small amount of the culture onto the slide and mix, 3-allow smear to air dry, 4-flame the slide
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