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Physiological Unknown Identification

Physiological Unknown Identification. Physiological Unknown. Initial Inoculation Media I) MacConkey agar is a Selective-differential culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation It contains:

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Physiological Unknown Identification

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  1. Physiological Unknown Identification

  2. Physiological Unknown Initial Inoculation Media I) MacConkey agar is a Selective-differential culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation It contains: Bile salts (to inhibit most Gram-positive bacteria, except Enterococcus and some species of Staphylococcus), crystal violet dye (which also inhibits certain Gram-positive bacteria), neutral red dye (which stains microbes fermenting lactose), lactose and peptone. Growth: Gram Neg Red Colonies: Lactose fermenter Colorless colonies: Non-lactose fermenter

  3. II) Eosin Methylene Blue Agar • Selective-differential medium for the isolation of gram-negative bacteria. It is especially used in the isolation of coliforms • EMB agar is selective because the aniline dyes in this purple media inhibit growth of Gram-positive organisms. Lactose fermenters metabolize the lactose in the media and produce acid byproducts, causing a color change in the colony. Thus, EMB is also a differential medium. • Strong acid production by organisms such as E. coli results in a metallic green sheen. • Weaker fermentation of lactose results in colonies with a pinkish-purple color. • Colonies of nonlactose fermenters remain colorless, or at least are no darker than the color of the media. • III) Nutrient Agar (Rich medium): Detection of colony types

  4. MacConkey Agar Results Macconkey agar with lactose(left) and non-lactose(right) fermenters

  5. Eosin Methylene Blue Agar Results 1: Gram-negative bacterium (Growth +).  Green metallic sheen: lactose fermented with strong acid end-products. 2. Gram-negative bacterium.  Non- lactose fermented 3: Gram –neg. Pink color: ferments lactose to weak acid end-products. 4: No growth: Gram +

  6. Hektoen Enteric Agar • The high peptone content offsets the inhibitory effect of bile salts on Shigella species in particular. The additional carbohydrates (sucrose and salicin) give better differentiation than lactose alone. The thiosulphate and ferric citrate are present to detect H2S-producing organisms. • AppearanceDehydrated medium: Pale green coloured, free-flowing powderPrepared medium: Green to dark green coloured gel After growth: Shigella: Green, moist raised colonies Salmonella: Blue-green colonies with or without black centres Coliforms: (rapid lactose/sucrose/salicin fermenters) Salmon-pink to orange colonies surrounded by a zone of bile precipitation

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