lab1细菌的革兰氏染色.PDF

1 Since bacteria are almost colorless and therefore show little contrast with the broth in which they are suspended, they are difficult to observe when unstained. Staining microorganisms enables one to: -see greater contrast between the organism and the background, differentiate various morphological types (by shape, arrangement, gram reaction, etc.), -observe certain structures (flagella, capsules, endospores, etc.) •Simple stains Simple stains highlight the organism so basic structures are visible in microscope. • Differential stains Differential stains react differently with different kinds of bacteria. • Special stains Used to color and isolate various structures, such as capsules, endospores, and flagella. Simple stains 2 2 Gram Stain - developed Christian Gram in 1884 The gram stain is the most widely used staining procedure in bacteriology. It is called a differential stain since it differentiates between gram-positive and gram-negative bacteria. Bacteria which stain purple with the gram staining procedure are termed gram-positive; those which stain pink are said to be gram- negative. Gram-positive and gram-negative bacteria stain differently because of fundamental differences in the structure of their cell walls. Structure of a Gram-Negative Cell Wall Structure of a Gram-Positive Cell Wall 24 h 24 h 1 min1 min 95%20 s 1 min Smear preparation Heat fixing Staining crystal violet stain wash with