Bacteria was not well known around the 1800's. Many people were getting sick and dying, which raised a few eyebrows. German physician, Robert Koch, used postulates which were a series of tests created to prove the existence of microbes. There are three main types of bacteria, coccus which is spherical, spirillum a spiral shape, and bacillus which is rod-shaped. Bacteria multiply using binary fission. Some bacteria have thick cell walls which make a dye called Gram stain, these are known as Gram-positive bacteria. The other bacteria have thin cell walls that do not absorb the dye and these are known as Gram-negative bacteria. Bacteria use enzymes to break down sugars chemically, this process of bacterial metabolism is called fermentation. Lactic acid is the waste product from lactic acid bacteria. Lactic acid lowers the pH of milk which makes it acidic. In this lab we will be isolating bacterial strain in yogurt samples in petri dishes, and then apply the bacteria to milk to examine if the milk will transform into yogurt.
