infectious diseases
Overview of Bacteria
Staining
 is the most common stain for general bacterial identification. Gram-positive bacteria retain crystal violet dye (appearing dark blue) after iodine fixation, alcohol decolorization, and counterstaining with safranin; gram-negative bacteria, which do not retain crystal violet, appear red. Gram-negative bacteria have an additional outer membrane containing lipopolysaccharide (endotoxin), increasing the virulence of these bacteria. (For other factors that enhance bacterial pathogenicity, see Factors Facilitating Microbial Invasion .) . They also can identify the gram-positive bacilli Nocardiosis and the protozoans Fluorochrome stains(eg, auramine-rhodamine) also identify acid-fast organisms, but a special fluorescent microscope is required. 