The Gram Stain

The gram stain is the most frequently used stain in a clinical microbiology laboratory and is usually the first step in identifying bacteria. Based on differences in cell wall components, bacteria are categorized as either gram-positive (stains dark purple) or gram-negative (stains pink). In addition to the gram reaction, the morphology and configuration of the bacteria can be observed, i.e., gram-positive coccus in chains or gram-negative rod.

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