Question #1: In 1835, Bassi showed that a fungus caused a silkworm disease, and in 1865 Pasteur discovered that a protozoan caused another silkworm disease. Why do we use Koch's postulates instead of Bassi's or Pasteur's postulates?
Answer #1: Koch was the major mind in establishing that microorganisms cause a specific disease. He was able to prove that certain bacteria was present in the blood of the infected person or animal, but the presence of the bacteria could have been caused by the disease. Koch proved that certain infectious diseases are caused by certain microorganisms that can be isolated and cultures onto a media. The requirements Koch established are that the same pathogen ...view middle of the document...
Bacteria that retain the purple color after this process is a gram-positive bacterium and bacteria that lose the purple color are gram-negative bacterium. These results are not universally applied because some bacterial cells stain poorly or not at all. The Gram reaction is most accurate when used on growing and young bacteria.
Question 4: Compare and contrast gram-positive and gram-negative cell walls with regard to (a) sensitivity to antimicrobial agents, (b) resistance to phagocytosis, (c) chemical composition, and (d) decolorization by alcohol.
Answer 4: Gram positive cell walls have many layers of peptidoglycan which forms a thick and rigid structure. The cell wall also contains teichoic acids and phosphate. The teichoic acids in the cell wall make it possible to identify gram-positive bacteria in testing. When alcohol is applied to gram-positive bacterium it makes it more impermeable to the violet iodine and it keeps the purple color. Gram positive cells are easily killed with penicillin’s and cephalosporins. Gram negative cell walls are made of one a just a few layers of peptidoglycan and an outer membrane. They do not contain teichoic acids. With the small amount of peptidoglycan, gram negative cell walls are susceptible to mechanical breakage. The gram negative cell wall provides block to some antiobiotics (penicillin) and digestive enzymes, but it does allow nucleotides, amino acids and iron to enter due to the presence of porins. When stained, gram negative cell wall is dissolved by alcohol and leaves a hole in the peptidoglycan layer that allows the violet iodine to diffuse. Once the safranin is applied it turns the cell pink.
Question 6: You look in the refrigerator and find an orange drink you had forgotten was there. The drink now has an off-taste and it bubbles. What is the most likely explanation for the changes in the drink?