The Gram stain provides a lot of clinically useful information but it won’t give you all the information you need for identification and tre


The Gram stain provides a lot of clinically useful information but it won’t give you all the information you need for identification and treatment. About which of these do you NOT learn anything from the Gram stain?

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Thu Thủy 6 months 2021-07-21T05:46:45+00:00 1 Answers 246 views 0

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    Answer: d) The ability of the bacteria to process nutrients.


    Incomplete question.


    a) Structure of the cell wall b) Bacterial morphology c) Susceptibility to antimicrobial drugs d) The ability of the bacteria to process nutrients.

    Gram staining is a type of differential staining to study bacteria, and is used to see cell morphology and to differentiate between gram-positive bacteria that appear violet and gram-negative bacteria that appear pink or red.

    To perform the staining, fix the samples with methanol for one minute or heat and add a dye called crystal violet and wait one minute. Then rinse with water and add lugol for one minute. Then add acetone alcohol for 5-30 seconds. At this point, gram-negative bacteria discolor while gram-positive bacteria do not. After this, a contrast staining is performed by adding safranin or basic fuchsin for one minute. This stain will turn the gram-negative bacteria pinkish-reddish.

    Crystal violet is a cationic dye that penetrates all bacteria through the bacterial wall. Lugol is a compound consisting of iodine and potassium iodide and acts as a mordant. The iodine enters the bacteria and forms an insoluble complex with the crystal violet, causing the crystal violet to bind more strongly to the bacterial cell wall. The added alcohol and acetone are used for decolorization, since the iodine/violet crystal complex is soluble in the alcohol and acetone. Thus, gram-positive bacteria do not decolorize, while gram-negative bacteria do.

    A contrast stain such as safranin or fuchsin is used to highlight gram-negative cells. After contrast staining, gram-negative cells are pink or red, while gram-positive cells remain purple.

    The wall of gram-positive bacteria consists of about forty layers of peptidoglycan which does not allow alcohol to pass through it because it is very thick, while that of gram-negative bacteria consists of a single layer of peptidoglycan. These differences cause gram-positive bacteria to retain the violet color and gram-negative bacteria to discolor.

    So, with this type of staining we can certainly see the structure of the cell wall, because those that retain the violet dye even after treatment with a decolorant are gram-positive (many layers of peptodoglycan) and those that easily lose the first dye and take up the second are gram-negative (single layer). It also gives us an idea of the shape and morphology, which when stained will be visible under the microscope.

    It also informs us about susceptibility to antibiotics, since some act only on gram-positive bacteria and others only on gram-negative bacteria. For example, gram-positive bacteria are sensitive to beta lactamase/penicillinase and gram-negative bacteria are susceptible to broad-spectrum penicillins such as piperacillin. However, this type of staining will not tell us about the bacteria’s ability to process nutrients, because that is not a process related to the structure of the cell wall.

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