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Microbiology - 005 - Gram Stain

The Gram stain is a fundamental tool used to differentiate bacteria by placing them into one of two general groups. Bacteria that are a deep purple after staining are called Gram + (positive), while bacteria that appear a lighter pink are called Gram - (negative.) Becoming familiar with the Gram stain technique is essential and it is often the first step in identifying an unknown bacterium.