of baktron "stick, rod," from PIE *bak- "staff used for support." So called because the first ones observed were rod-shaped. Bacteria are unicellular, micrscopic organisms that lack chlorophyll and multiply (repoduce) by binary fission (simple cellular division).Įtymology. The ribosomes are not organized into a nucleus (i.e., the DNA is not bound my a membrane. When a simple stain is done, only one stain is applied to the cells to better see the cells using the microscope.Ī good stained smear should be somewhat difficult to see with the naked eye on the surface of a microscope slide.A bacterium is a prokaryotic (containing small ribosomes (70S)) organism. Negative stains produce a darker background and cells appear light and unstained. Acidic stains can stain positively charged molecules in cells including some proteins. Negative stains include India ink and nigrosin. Basic stains are attracted to negatively charged molecules in the cell including nucleic acids (DNA and RNA) and some proteins. Acidic stains can be positive stains (stain the cells) or they can be negative stains (stain the background and not the cells). Acidic stains include eosin, acid fuchsin, rose bengal, and congo red. Basic stains include methylene blue, crystal violet, malachite green, basic fuchsin, carbolfuchsin, and safranin. Table 1: Common simple stain types include basic stains (high pH stains), acidic stains (low pH stains), and negative stains (stains the surroundings of cells instead of the cells themselves). The image to the right shows that the bacterial cell morphology is cocci (round) and the arrangement is in clusters or bunches, often distinguished with the prefix staphylo- (putting these two terms together, these bacteria can be described as staphylococci indicating they are round-shaped bacteria that occur in clusters or bunches. The presence of negatively charged molecules in the cell (like DNA & RNA) causes the cell to stain blue. It is a cationic dye (positive charge) which stains the cell a blue color. These features cannot be distingushed using a simple stain.įigure 1: Methylene blue is a simple and direct stain used for determining bacterial morphology (shape and arrangement). cell wall structures, presence or absence of endospores, presence or absence of capsules, presence or absence and arrangement of flagella, etc.). Other staining approaches utilize more than one stain ( differential stains) and can be used to determine other differences of between different bacterial species (e.g. Simple stains can be used to determine a bacterial species’ morphology (cell shape) and arrangement (single, chains, clusters, etc.), but they do not give any additional information. Some stains commonly used for simple staining include crystal violet, safranin, and methylene blue. One type of staining procedure that can be used is the simple stain, in which only one stain is used, and all types of bacteria appear as the color of that stain when viewed under the microscope. This type of information can help scientists identify and classify microorganisms, and can be used by health care providers to diagnose the cause of a bacterial infection. Some staining techniques can be used to determine the cells’ biochemical or structural properties, such as cell wall type and presence or absence of endospores. Several types of stains can be used to make bacterial cells more visible. Most types of cells do not have much natural pigment and are therefore difficult to see under the light microscope unless they are stained.
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