Gram-negative bacteria do not retain the crystal violet stain during Gram's staining method and instead absorb the red counterstain. This occurs because these bacteria have a cell wall made up of a thin layer of peptidoglycan. Many bacteria that typically inhabit the human body and can cause diseases, including gonococci and meningococci, are Gram-negative. Additionally, the pathogens responsible for diseases like bubonic plague also fall into this category. The Gram staining technique was invented by the Danish bacteriologist J.M.C. Gram (1853-1938) and utilizes a dye known as crystal violet. This method allows for the differentiation of bacteria based on their ability to retain the crystal violet stain, classifying them as either Gram-positive or Gram-negative.
