Gram and acid-fast stains Four bacteria and a polymorphonuclear neutrophil are shown at each stage All are initially stained purple by crystal violet and iodine of Gram stain (A1) and red by carbol-fuchsin of acid-fast stain (B1) After decolorization, Gram-positive and acid-fast organisms retain their original stain o Others are unstained (A2, B2) Safranin of Gram counterstain stains o Gram-negative bacteria and makes background red (A3), and methylene blue leaves a blue background for contrasting red acidfast bacillus (B3)
Ryan KJ and Ray CG Eds. Sherris Medical Microbiology, 5th Ed. New York: McGraw-Hill, 2010.