2 - What is considered to be \"too old\" for a culture of Gram-positive bacteria

Question

2 - What is considered to be "too old" for a culture of Gram-positive bacteria, like B, megaterium, to be used for the Gram stain? 3-What would happen if you used an old culture of a Gram-positive bacterium like B megaterium? What would you view as the result? Why? 4 - Describe THREE differences between Gram-positive and Gram-negative cell envelopes. 5 - How does penicillin work to kill bacteria? Which type of bacterium is more likely to be killed by penicillin- Gram-positive or Gram-negative - and why?

Explanation / Answer

2. A culture of gram-positive bacteria which is about 12-14 hours old is considered to be used for Gram stain. More than 14 hours old culture is considered as "too old" to be used for gram stain.

3. An old culture of gram-positive bacterial cells may not retain the stain properly as compared to the younger culture, thus, giving false negative results such as pink colored colonies. The gram-positive cells are seen as purple colored colonies in general.

4. The three differences between the gram-positive and gram-negative cell envelope are as follows:

5. Penicillin hinders in the cross-linking process of bacterial cell wall synthesis by preventing peptidoglycan linkage which weakens the cell wall and causes the bacterium to lyse, or kill, because of osmotic pressure. Penicillin is more likely effective against Gram-positive bacteria because the Gram-negative bacteria have a lipopolysaccharide layer which surrounds the peptidoglycan layer of the cell wall, thus, preventing the penicillin from killing the bacteria.

Gram-positive Gram-negative i) does not have an outer membrane. i) have an outer membrane. ii) have thick, multilayered peptidoglycan wall ii) have thin, single layer lipopolysaccharide wall. iii) have teichoic acids in the cell wall. iii) does not have teichoic acids in the cell wall.

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