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MMG 464 NOTES EXERCISE 0 Aseptic Techniques Aseptic technique – the precautionary measures used to avoid contamination of cultures Exercise 1 Growth Media - liquids = broths - solidified with agar, a complex poly saccharide that has unusual melting and gelling properties, once solidified a medium containing agar will remain solid until heated to about 100 again o (behavior is called hysteresis) – provides advantages in certain bacteriological procedures o second useful property is that very few bacteria degrade agar - 2 types of common growth medias o Broth Brain heart Infusion (BHI) – for cultivation of fastidious, as well as other pathogens including streptococci, pneumococci, meningococci, corynebacteria, staphylococci, arcanobacteria and other GRAM (+) orgaisms o Solid Trypticase Soy Agar – for isolation and cultivation of a variety of pathogens including Brucella and streptococci. Contains flucose as the fermentable source of energy, a tryptic digest of protein as a source of amino acids and peptides - both media’s very rich sources of nutrients for bacteria and are well-suited for growing pathogens, which lack the nutrional versatility of ordinary bacteria Pure Culture Techniques: the streak plate - pure culture : is defined as a population of a single species of microorganisms growing in or on a medium - colony : the macroscopically visible growth of a microorganism on an agar plate that usually arises from a single, isolated cell - to be able to study the morphological cultural and biochemical characteristics of a single bacterial species, it should be separated from other bacterial species and obtained in pure culture - a pure culture of an organism is essential for its identification, for doing antibiotic sensitivity testing, for prep of specific vaccines - streak plate procedure, involves dilution of inoculum on a loop by systematically streaking it over the agar surface in a Petri plate to obtain isolate colonies – most common - streak plate useful in studying morphology and characteristics of isolate colonies Action of Bacteria on Blood - addition of blood to a growth medium generally enhances the nutritional value of the medium but some microbiologists argue that blood media are iron-poor because of the high avidity of the iron-binding protein, transferring – primary way to isolate pathogens
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- blood in medium is advantageous… o many bacteria produce enzymes called hemolysisn that cause hemolysis (breakdown of red blood cell membranes) o alpha-hemolytic = show a narrow zone of greenish discoloration- unhemolyzed red cells o beta-hemolytic = show a clear zone around colonies, red cells are totally disintegrated o gamma-hemolytic = nonhemolytic organisms o hemolytic reactions are of significance in identification of gram positive cocci, little use for id-ing gram-negatives, as gram negatives are generally beta-hemolytic - appearance of hemolysis associated with any bacterial colony will be determined in part by nature of blood in medium – some hemolyze sheep blood but not horse
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