Tiêu đề 9. IDENTIFICATION OF BACTERIA WITH EMPHASIS TO DIFFERENT STAINING TECHNIQUES AND BIOCHEMICAL REACTIONS.pdf ✅

PHARMD GURU Page 1 INTRODUCTION:  Microorganisms in nature are never found in pure populations.  Different types of mixed microorganisms are normally present in soil, water, food, air and various parts of the human or animal body.  To study the role played by a specific microorganisms in these environments, it is necessary to isolate the microorganisms in pure culture.  It is extremely important to maintain isolated pure cultures for extended periods in a viable condition.  Most microbiological laboratories usually maintain a large collection of pure cultures as well as subcultures of authentic species purchased from various culture collection centres. Ex: American Type Culture Collection (ATCC), U.S.A; National Collection of Industrial Bacteria (NCIB), Scotland; National Collection of Yeast Cultures (NCYC), England; National Collection of Type Cultures (NCTC), England; National Chemical Laboratory (NCL), India etc.  Identification of unknown bacterial cultures is one of the major responsibilities of a microbiologist.  Samples of blood, tissue, water, food and cosmetics are examined daily in laboratories throughout the world for the presence of contaminants and pathogenic microorganisms.  Pharmaceutical industries and research institutes are constantly screening soil, water, marine samples to isolate new antibiotic, enzyme and vitamin producing microorganisms.  Once these unknown important microorganisms are isolated they must be identified and classified. IDENTIFICATION OF BACTERIA WITH EMPHASIS TO DIFFERENT STAINING TECHNIQUES AND BIOCHEMICAL REACTIONS
PHARMD GURU Page 2 The science of classification is called taxonomy. Bergey's Manual of Systemic Bacteriology has been the official, internationally accepted reference for bacterial classification. In the current edition of Bergey's manual, bacteria is classified into 33 groups called sections rather than into the classical taxonomic groupings of phylum, class, order and family. The relationship of microorganisms in each section is based on characteristics such as morphology, staining reactions, nutritional requirements, physiological properties, cultural characteristics, biochemical tests, serological properties, pathogenicity and genetic characterisation. MORPHOLOGY:  The morphology of microorganisms depends on a number of factors such as the stain studied, nature of culture medium, temperature and duration of incubation.  The size, shape and arrangement of cells is determined by microscopic examination of stained smears. The shape may be spherical, rod, filamentous, comma like or spiral.  They may be arranged singly, pairs, tetrads or in packets of eight or in chains. Unstained wet film or hanging drop preparations are examined under a light microscope for observation of motility.  They may be non-motile (absence of flagella) or motile with monotrichate, lophotrichate, amphitrichate or peritrichate flagella.  The spores may be oval, spherical or ellipsoidal if present. STAINING REACTIONS: To study size, shape, arrangement and properties and differentiate specific groups of microorganisms, biological stains are used. Stain is an organic compound containing a benzene ring with chromophore and auxochrome group. Different staining techniques are used for visualisation, differentiation and separation of bacteria in terms of morphological characteristics and cellular structures. 1) SIMPLE STAINING: In simple staining, the bacterial smear is stained with a single stain e.g. methylene blue, crystal violet, carbol fuchsin, safranin, etc. Basic stains with a positively