History of Gram Stain

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" height=90 BGCOLOR="#CCFF99" TEXT="#080000"> <div> <B> </B><A HREF="index_avianitarian.htm" TARGET="_top" TITLE="AVIANITARIAN Reference Guide "><B>home</B></A><B> | </B><A HREF="microscope.htm" TARGET="_top" TITLE="The Microscope for Aviculture Microbilo">The Microscope  for Aviculture Microbilogy</A>   |   <A HREF="id103.htm" TARGET="_top" TITLE="Microscope Questions">Microscope Questions</A>   |   <B>History of Gram Stain</B>   |   <A HREF="id112.htm" TARGET="_top" TITLE="Gram Staining">Gram Staining</A>   |   <A HREF="id151.htm" TARGET="_top" TITLE="Fecal Flotation">Fecal Flotation</A>   |   <A HREF="id185.htm" TARGET="_top" TITLE="Flotation continue">Flotation continue</A></div> <div> </div> </td> </tr><tr> <td valign="top" height=390 BGCOLOR="#CCFF99" TEXT="#080000"> <div> <I>History of Gram Stain</I></div> <div>  <FONT SIZE="3" COLOR="#000000" FACE="Arial" >In 1884, Hans Christian Gram, a Danish doctor working in Berlin, accidentally stumbled on a method which still forms the basis for the identification of bacteria.</FONT></div> <div> While examining lung tissue from patients who had died of pneumonia, he discovered that certain stains were preferentially taken up and retained by bacterial cells. With a few years, Gram developed a staining procedure which divided almost all bacteria into two large groups - the Positive and Negative - Purple and Pink.</div> <DIV ALIGN="LEFT"></DIV> <div> <FONT SIZE="3" COLOR="#CC0000" FACE="Arial" >   </FONT><U>GRAM STAINING</U> </div> <div> Can you imagine that a staining procedure devised more than a century ago</div> <div> would still serve as one of the most serious procedures for bacterial classification? Today, Microbiologists still feel grateful to the Danish physician Christian Gram, who invented the gram-staining method in 1884. </div> <div> To do a gramstain, an aviculturist smears a sample of bacteria on a slide, fixes it with heat, and soaks it in a violet dye. Then rinses the slide and soakss it with iodine. The slide is rinsed again with water, then with alcohol or discolorization and counterstained with a pink dye called safranine for a moment. The cell walls of gram-negative bacteria have a very low tolerance for the violet stain, which is decolorized by the alcohol.</div> <bR> <div> Once counterstained with safranine,  the gram-negative bacteria appear bright pink to red. Gram-positive cell walls have a high tolerance for the violet stain, and retain it even through the alcohol or decolorizing rinse. When the process is</div> <div> complete, they appear dark purple to brown.  The difference between the two cell types appears to be in the amount of peptidoglycan in the cell wall. Gram positive cell walls are about five times as rich in peptidoglycan as gram-negative </div> <DIV ALIGN="LEFT"></DIV> <div> cell walls.  Gram-negative bacteria have a second membrane (chemically different from the plasma membrane) external to the cell wall, and may also have a gelatinous sheath external to the second membrane. </div> <div> The differences in the cell wall are more than simply a classification/diagnosis  tool. Cell wall characteristics are intimately related to the disease-causing potential of the bacterium. In fact, medical researchers have found that an extremely effective way to combat bacterial pathogens is by interfering with cell wall formation. Because the eukaryotic cell has no analog to the prokaryotic cell wall, medicines which target bacterial cell walls have little or no effect on plant or animal cells.</div> <bR> <bR> <bR> <bR> <bR> <bR> </td> </tr></table></body>