In Mycobacterium staining, the counterstain overtakes the cells and bacteria are being masked. Which of the following is a likely cause?

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Multiple Choice

In Mycobacterium staining, the counterstain overtakes the cells and bacteria are being masked. Which of the following is a likely cause?

The key idea is contrast in acid-fast staining. In Ziehl–Neelsen staining for Mycobacterium, after the acid-fast bacilli retain the red primary stain, the counterstain colors the non–acid-fast background (blue) to create a clear contrast between the red bacteria and the surrounding cells. If the counterstain isn’t used at all, there’s no blue background to contrast with the red bacilli, so the field can look dull or the bacteria can seem to be masked by the surrounding tissue. This is why omitting the counterstain is the likely cause of the observed masking. The other options affect staining intensity or decolorization timing but don’t directly explain a lack of contrast due to skipping the counterstain.

The key idea is contrast in acid-fast staining. In Ziehl–Neelsen staining for Mycobacterium, after the acid-fast bacilli retain the red primary stain, the counterstain colors the non–acid-fast background (blue) to create a clear contrast between the red bacteria and the surrounding cells. If the counterstain isn’t used at all, there’s no blue background to contrast with the red bacilli, so the field can look dull or the bacteria can seem to be masked by the surrounding tissue. This is why omitting the counterstain is the likely cause of the observed masking. The other options affect staining intensity or decolorization timing but don’t directly explain a lack of contrast due to skipping the counterstain.

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