Most microorganisms are essentially transparent when examined by optical microscopy with bright field illumination. Phase contrast microscopy (PCM) employs a contrast-enhancing optical mechanism that allows microorganisms to be viewed in their natural state; PCM allows for examination of dynamic events in living cells. The contrast-enhancing mechanism that is the basis of PCM involves translation of minute phase shifts that occur as light waves pass through a microorganism into changes in wave amplitude; these changes are perceived by the viewer as differences in image contrast. This increase of image contrast allows the microorganism to be visualized without the use of deleterious killing, fixing and staining procedures required for standard optical microscopy. PCM is a type of light spectroscopy that exploits the change in wavelength that occurs when light travels through a transparent sample to create clearer images. PCM is used for imaging biological samples at the cellular level without the need for staining or other invasive sample preparation methods.