A Day in the Park It was a lovely October afternoon-the sun was shining and Sam

Question

A Day in the Park It was a lovely October afternoon-the sun was shining and Sam was having a great time at the dog park with his dog, Scout. As the day came to a close, Sam was packing up Scout's toys when another dog tried to steal Scout's favorite chew toy. Without a second thought, Sam reached for the toy: unfortunately, the dog snapped at Sam and bit him on the forearm. It was a quick bite-it didn't bleed very much and didn't seem very deep. Sam washed the bite with soap and water when he got home and didn't give it another thought. The next morning, Sam noticed that the bite area was a little red and tender. As the day went on, the soreness and redness increased and Sam noticed that the area around the bite was also hurting. By the next morning, there was a pus-filled abscess present and his entire forearm was sore to the touch. Sam decides that he should go to the doctor ASAP. At the doctor's office, the doctor drains the abscess and takes a sample for culturing. She then performs gram-stain and the bacteria on the slide turns purple. a) What is the gram status of the bacterium? b) Explain in detail what would have happened to her gram stain if the lab technician had left the alcohol on too long. (You should explain in terms of what happens to the cell envelope and to the results of her stain)

Explanation / Answer

Question: a) What is the gram status of the bacterium?

Answer: Gram-positive bacteria remain purple as a result of the Gram stain procedure which enables bacteria to retain color of the stains, based on the differences in the chemical and physical properties of the cell wall.

Answer: b) Gram-positive bacteria are not decolorized by alcohol and will remain as purple. The decolorization step using alcohol must be performed carefully, otherwise over-decolorization may occur. This step is critical and must be timed correctly otherwise the crystal violet stain will be removed from the Gram-positive cells. If the decolorizing agent is applied on the cell for too long time , the Gram-positive organisms to appear Gram-negative. Alcohol has a dehydrating effect on the cell walls of Gram positive bacteria which causes the pores of the cell wall to shrink.

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