Study of respiratory symptoms among sputum positive

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times the number seen with the Z.N.stain. Mobasher et at (1984), reported
the advantages of the fluorescent microscopy as follow:
a) The bright fluorescent bacilli are much more obvious owing to increased
contrast against the dark background .
b) The bacilli can be recognized at a lower magnification.
c) The time required to search a smear effectively is much reduced.
d) It is difficult or impossible with Z.N. method to detect bacilli towards
r: the periphery ofthe field, however the fluorescence microscopy, the out
-;;. J in tissue.
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of focus images of the stained organisms can be detected even at the
extreme edges ofthe field.
David et aI. (1989), described nachtblau stain which stained the
AFB blue. They used neutral red or pyronine as a counter-stain. They
claimed that the blue bacilli against the red or yellow back ground are
easier to detect. Thomas et al. (1988), used silver salts to stain the M.T.B.
Toman (1979), found that false positive acid-fast smear may result
from: 1) The presence ofacid fast particles other than tubercle bacilli such
as certain food particles like waxes and oils, saprophytic AFB like M.
Kansasii or nocardia species, spores ofbacillus subtilis, fibers, pollens and
scratches on the slide.
2) Contamination through accidental transfer ofbacilli from one positive
+J smear to another negative one.
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