Microbiology

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Microbiology

• Lab Practice

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Gram Staining

• 1880s by Hans Christian Gram .
• Positive stain
• Differential stain uses two dyes, also classifies
  bacteria into two different groups Gram positive
  and Gram negative .

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Gram Staining

• The characteristics of Gram stain is due to the
  structure of the cell wall (presence of
  peptidoglycan and teichoic acid)

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Gram Staining

• Gram positive bacteria have a thick layer of
  peptidoglycan in the cell wall.
• Gram negative bacteria have an outer membrane
  (lipoprotein, lipopolysaccharide) and a thin
  layer of peptidoglycan).

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Gram Stain

• Crystal Violet (purple) primary stain, for 60
  sec
• Iodine the mordant, for 30-60 sec
• Alcohol decolorizer, for 30 sec or until no more
  color comes out of the slide
• Safranin (red) counterstain, for 60 sec

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Gram Staining

• The results
• - Gram positive bacteria appear purple
• - Gram negative bacteria appear red

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Gram Staining

• Nonpathogenic G- bacteria (E.coli, Proteus
  vulgaris, spirillum volutans)
• Nonpathogenic G staphylococcus albus
• Pathogenic G bacteria (streptococcus pyogenes,
  Bacillus anthracis, clostridium tetani )

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Gram Staining

• Staphylococcus aureus
• Escherichia coli

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