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I have acquired TB slides from my city's health center that are supposedly acid-fast bacteria (AFB) positive. However, when I took a look at it, I see basically no carbol fuchsin stains.

They were individually neatly folded in paper. When I opened them, the stains were slightly wet with immersion oil, facing down. So far, so good (page 6). I've been later informed that these samples were prepared Q1 2019. Based on my research, the staining solutions themselves last up to 12 months (page 33). I can't find any data on how long a stained sample would keep though.

Do they decolorize over time? I expected the AFB to be bright, or at least slightly pink, but I see no such thing. I do see bacilli, though all of them are nearly transparent/methylene blue in color.


Here are some sample images. The first 2 are how I expected AFB to look like, while the next 2 are what I captured (and I think should contain AFB). The last pic is a 10um/div calibration slide for reference.

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This TB study might help you: external page

Briefly, they used 6 to 19 months old samples of mostly bad quality (due to their age). The last sentence of the quote below sounds promising though.

The 12,543 sputum smears stored at the national TB reference laboratory for 6 to 19 months were stored at room temperature in a wooden slide box without a cover slip. Most of them had lost their stain reflecting the counterstaining with methylene blue. Restaining of 436 doubtful slides by ZN gave disappointing results throughout [...]

After a 6 to 19 months storage of ZN stained sputum smears in a non-air conditioned atmosphere, the bright red color of eggs due to carbolfuchsin had virtually disappeared. [...] In such case, the ZN restaining of sputum smears allows to rediscover AFB that were discolored.

When I did this the last time, we used fresh and few months old samples which looked similar to the first of your images. Just have a look at the paper, I guess.

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