Micro Lab
Introduction In 1844, Christian Gram devised one of the most important staining techniques used in microbiology, the Gram stain. Gram staining is based on the ability of the bacterial cell wall to retain the crystal violet dye during solvent treatment. There are four steps involved in Gram staining: first the bacteria is stained with crystal violet, the primary dye, then , a mordant is used, iodine. After this is done, a decolorize is applied, in this case ethanol, and finally the counterstain, safranin, is added on. If the bacteria retains the crystal violet dye, which is purple, it is considered to be Gram positive. However, if the bacteria is not stained by the crystal violet, but by the safranin, which is red, it is considered to be Gram negative. ( 1-2) B. subtilis is a rod shaped, gram positive bacteria. It is ubiquitous in nature( soil, water, and airborne dust), and in a variety of foods. B. subtilis causes two types of food borne illnesses, watery diarrhea and vomiting. It can be prevented by properly cooking or refrigerating food. A unique characteristic of this bacteria is its ability to produce endospores when environmental conditions are stressful. The B. subtilis genome is widely used for the production of enzymes and specialty chemicals. (3) E. coli is an emerging cause of food borne illness. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness. This infection often leads to bloody diarrhea, and occasionally to kidney failure. Most illnesses have been associated with eating undercooked, contaminated ground beef, or through person to person contact. E. coli can be prevented by washing your hands carefully, thoroughly cooking ground beef, and avoiding unpasteurized milk. (4) S. aureus is a gram positive bacteria that is usually arranged in clusters or clumps of cocci.