Page 58 - MNUmicrobiology practical 2025
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General Microbiology & Immunology (PM 401) second level Semester 4 2024/2025
Variations in Gram Reaction
• Over decolonization:
The Gram positive bacteria will stain with red color, due
to:
– Thin film
– More time in contact with Alcohol.
– Excess drying
– Concentration of the stain
– Age of culture.
• Under decolonization
The Gram-negative bacteria will stain with deep violet color, due to thick film or less time
in contact with alcohol.
You can watch this video for gram staining procedure
General Microbiology & Immunology (PM 401) Practical note Page 47
