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The Gram stain

The Gram stain. Thin smear/heat fix Gram stain: a. Flood slide with crystal violet and let stain for 1 minute. b. Drain off crystal violet and rinse off with distilled water ; flood slide with Gram's iodine for 1 minute. c. Rinse off Gram's iodine with distilled water.

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The Gram stain

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  1. The Gram stain Thin smear/heat fix Gram stain: a. Flood slide with crystal violet and let stain for 1 minute. b. Drain off crystal violet and rinseoffwith distilledwater; flood slide with Gram's iodine for 1 minute. c. Rinse off Gram's iodine with distilled water. d. Hold the slide on an angle (preferably with a clothes pin) and drop 95% ethyl alcohol onto it until the alcohol leaving the slide no longer has a purple tint; be sure to drop the alcohol onto the upperportion of the slide so that the smears are subjected to uniform decolorization. Be careful not to "decolorize" dye from the clothes pin!! e. Rinse with distilled water and flood the slide with safranin and let stain for 2-3 minutes. f. Rinse with distilled water and blot dry with bibulous paper. Gram positive Gram negative

  2. Gram-positive cell wallsGram-negative cellwalls The characteristic compound found in all true bacterial cell walls is peptidoglycan. The amount of PPG is among one of the differences between the GP and GN cell walls. • Thick peptidoglycan • 90% peptidoglycan • Teichoic acids • 1 layer • Not many polysaccharides • In acid-fast cells, contains mycolic acid • Thin peptidoglycan • 5-10% peptidoglycan • No teichoic acids • 3 layers • Outer membrane has lipids, polysaccharides • No acid- fast cells (mycolic acid)

  3. Examples: • Examples of gram-negative bacteria:Spirochetes (spiral-shaped) - causes syphilis, lyme disease Neisseria (cocci) - causes meningococcus, gonorrhea • Our Favorite: E. coli!!

  4. Six common gram-positive bacteria that infect humans and their shapes follow:Streptococcus (cocci)Staphylococcus (cocci) Bacillus (bacilli, protective spore) - causes anthrax and gastroenteritis Clostridium (bacilli, protective spore) - causes botulism, tetanus, gas gangrene, and pseudomembranous colitis Corynebacterium (bacilli, no protective spore) - causes diphtheria Listeria (bacilli, no protective spore) - causes meningitis

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