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This paper honors Hans Christian Joachim Gram. In published papers, he simply identified as Christian Gram. Gram devised a staining technique that is still used to identify and classify different types of bacteria. He was a Danish microbiologist, born in Copenhagen on September 13, 1853. In German microbiologist Karl Friedländer’s lab, Gram noticed that staining a smear of pneumonia bacteria with a crystal violet followed by iodine and organic solvent showed differences in various samples. “Gram-negative” bacteria have thin cell walls that allow the solvent to wash away part of the stain. “Gram-positive” bacteria appear purple in microscopy because their cell walls are thicker, so the stain cannot leave. Today, the Gram classification is fundamental to bacteria identification, classification, taxonomy, and clinical application (drug therapy) in medicine. His discovery is of great use in the identification and classification of bacteria, especially for pathogens of infectious diseases. It is also useful in deciding how to treat infections since some antibiotics are active only against gram-positive bacteria and others against gram-negative bacteria.

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