|Description:||This is a photomicrograph of a Gram-stained urethral exudate sample from a male who presented with a case of urethritis. In this particular view, numbers of polymorphonuclear leukocytes (PMNs) were visible, however, no organisms were evident. This specimen proved to be negative for the presence of Gram-negative Neisseria gonorrhoeae bacteria.|
Gram-stain is a histochemical technique used by microbiologists to differentiate microorganisms into two large groups, that of Gram-negative, or Gram-positive bacteria. Gram-positive bacteria stain a dark violet-blue, for the crystal-violet stain binds to the exterior cell wall of these organisms. On the other hand, Gram-negative bacteria bind with the counterstain, in this case, the safranin or fuchsin stain. This technique is yet another method by which the trained laboratorian identifies pathogens, in order to come to a diagnostic conclusion.