Laboratory Report 15 Draw cells from the Gram-stained slides, and lahel each bac
ID: 199043 • Letter: L
Question
Laboratory Report 15 Draw cells from the Gram-stained slides, and lahel each bacterial species. Based on your results, note the Cram reaction cell shape, and cell arrangement of each bacterium in the given table. Verify these results to determine if you are correct P aerugiosa and SaureMs B. megaterium and E. coli M. catarrhaliy 1. Why is the Gram stain considered a differential stain? 2. How do gram-positive and gram-negative bacteria differ in cellular structure, and how does this tribute to their differential staining properties? How does the age of a culture affect the Gram stain reaction? What is an optimum culture age for a valid Gram reaction? 3.Explanation / Answer
1. S. aureus:
S. aureus should be purple (gram-positive) cocci in singles, pairs, short chains, and clusters.
2. P. aeruginosa:
P. aeruginosa should be pink (gram-negative) bacilli in singles and pairs.
3. B. megaterium:
B. megaterium should be very large purple (gram-positive) bacilli with or without clear spots representing spores (depends on age of the culture) in pairs or chains.
4. E. coli:
E. coli should be short pink (gram-negative) bacilli in singles.
5. M. catarrhalis:
M. catarrhalis should be pink (gram-negative) cocci in pairs (diplococci).
B. short Answers:
1. ANS: The Gram stain differentiates two types of bacteria based on the composition of their cell walls. It uses a primary stain, a mordant, a decolorizer, and a secondary stain to allow for the visualization of these structural differences.
2. ANS: a gram positive cell, which has a thick cell wall, retains the crystal violet dye better in the presence of a decolorizer as compared to a gram negative cell, which has a thin wall
3. ANS: Old cultures of gram-positive cells may not retain stain as well as younger cultures and could give false negative results, i.e., pink cells. Cultures that are 16-18 hours old are best.
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