GeneralMicrobiology[2] - General Microbiology This...

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General Microbiology This information was created by those at “theeseller555.” This item is to be sold only by theeseller555. GENERAL Bacteria are unicellular microorganisms having a variety of characteristics allowing their classification. One major classification scheme is based upon their staining properties using the "Gram stain" procedure. In this procedure, heat-killed bacteria are exposed to the purple dye crystal violet and iodine. This combination forms a dye complex in the bacterial cell wall. Treatment of the stained bacteria with a decolorizer like ethanol will wash away the dye complex from some bacteria but not others. Bacteria that retain the crystal violet-iodine complex appear purple and are called "Gram-positive". Bacteria that lose the dye complex can be counterstained with the red dye saffranin so that they appear red. These bacteria are called "Gram-negative". The basis of the Gram reaction lies within the structure of the cell wall, described below. Bacteria also come in many different shapes. Spherical shapes are referred to as "cocci" while elongated cylinders are called "bacilli" or "rods". Some bacteria are slightly elongated cocci and these are referred to as "coccobacilli". Even other bacteria have a corkscrew-like appearance; these spiral forms are often called "spirochetes". Individual cells may also be arranged in pairs or clusters or chains. Thus, may morphologies are possible and these can be useful for the identification of bacterial genera. The ability of a bacterium to cause disease is known as its virulence. In terms of the medical aspects of bacterial structure , we are most interested in those features that interact with the host. These features are found predominantly on the outer surface of the bacterial cell. This page will describe some of these features. SURFACE APPENDAGES Bacteria may or may not possess surface appendages that provide the organism with the ability to be motile or to transfer genetic material or to attach to host tissues. These appendages are outlined below: 1. Flagella : These are the organs of motility. Flagella are composed of flagellins (proteins) that make up the long filament. This filament is connected to a hook and rings that anchor the flagella in the cell wall. In Gram-positive bacteria, there are two rings attached to the cytoplasmic membrane; in Gram-negative cells, an additional two rings are found in the outer membrane. Flagella may be up to 20 μm in length. Some bacteria possess a single polar flagellum (monotrichous), others have several polar flagella (lophotrichous), others have several flagella at each end of the cell (amphitrichous), and still others have many flagella covering the entire cell surface (peritrichious). Counterclockwise rotation of the flagella
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produces motility in a forward motion; clockwise rotation produces a tumbling motion. Flagela may serve as antigenic determinants (e.g. the H antigens of Gram-negative enteric bacteria). 2.
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This note was uploaded on 05/02/2008 for the course PCAT PCAT taught by Professor Unknown during the Fall '08 term at University of Washington.

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GeneralMicrobiology[2] - General Microbiology This...

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