staining of bacterial cells

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• Assist. Prof. Nagham Mohammed
• College of Veterinary MedicineBaghdad University

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Observation of bacteria with conventional bright
field microscopy yields relatively little useful
information. This is because of the lack of
contrast coupled with the small size of the
bacterial cell. The stains react chemically
with cell material will enhance the contrast
between the cell and the background.
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A stain is a dye consisting of a colored ion (a
chromophore) and a counter ion to balance the
charge. staining reaction is Attachment
of the chromophore part of the dye complex to a
cellular component .
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• Depending upon the dye, the chromophore can be
• either positive charge (cationic) and have an
  affinity for negative ions.
• or negatively charged (anionic) with an affinity
  for positive ions.
• Bacteria carry anet negative charge at pH 7.

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• Cationic dyes such as ( methylene blue, basic
  fuchsin, or crystal violet ) Will directlly
  staining of Bacterial cells.

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• anionic stains such a ( eosin and nigrosin)
  will not directly stain bacterial cells.
• negatively charged stains, are useful for
  revealing the outlines of bacterial cells.
• anionic dyes stain the background, leaving the
  bacterial cells clear and bright against a dark
  background.

stain the background