What is the principle of direct staining?

The principle of direct staining is to provide significant contrast between the microbial cell and its environment to study a cell's morphology. Direct staining allows for the observation of the shape, size, and arrangement of bacterial cells. The cell walls of the majority of bacterial cells possess an overall net negative charge and therefore are stained directly with a basic, positively charged chromophore single stain. The opposite charges attract one another. During a direct stain procedure, the cells are the only ones that become colored, while the background stays colorless. Direct staining uses basic dyes such as crystal violet, safranin, and methylene blue. These dyes ensure that there is enough contrast to be seen under the microscope.