• A general purpose and nutritious medium for the non-selective enrichment of non-fastidious and some fastidious organisms. Tryptone and soy peptone are the nitrogen and vitamin source in the medium. Glucose is the carbon energy source that facilitates organism growth and sodium chloride maintains osmotic balance. Di-potassium hydrogen phosphate is a buffering agent to prevent auto-sterilisation due to acid production during the growth of some organisms. Tryptone Soya Broth is also commonly referred to as Soybean-Casein Digest Medium or Tryptic Soya Broth and is abbreviated as TSB. TSB conforms to the Harmonized United States Pharmacopoeia (USP), European Pharmacopoeia (EU), and Japanese Pharmacopoeia (JP).  
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  • Edwardsiella ictaluri medium is a selective medium for the isolation of Edwardsiella spp. based on the formulation by Shotts et al. (1) Edwardsiella spp. may be differentiated from other microorganisms on this medium due to its colony morphology. The peptones provide the required carbon, nitrogen and vitamins. Sodium chloride maintains the osmotic balance. Colistin and bile salts are selective agents to inhibit most Gram-negative and Gram- positive organisms. Mannitol is a fermentable carbohydrate and bromthymol blue is a pH indicator. Phenylalanine and ferric citrate are used to detect phenylalanine deaminase activity in Proteus spp. Agar is a solidifying agent. Shotts et al. (1) noted Proteus spp. swarming can overgrow on a mixed cultured sample. Therefore, a selective supplement (LS0021) may be added to the medium to restrict Proteus spp. swarming
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  • MacConkey agar No. 3 is a selective medium primarily for the isolation of Enterobacteriacae from waters and sewage. This media differs from the original MacConkey formulation in that as well as bile salts, crystal violet has been included as an additional selective agent. This has the effect of inhibiting Gram-positive organisms. The peptone acts as a nitrogen, carbon and vitamin source. Sodium chloride maintains osmotic balance. Lactose is a carbohydrate and during its fermentation causes a confined pH drop around the bacterial colony. This causes a colour change in the pH indicator, neutral red and bile precipitation.  
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  • Eosin Methylene Blue agar (EMB) is a selective medium primarily for the isolation of coliforms from clinical, food and environmental samples. This is the modified formulation of EMB proposed by Levine with a higher concentration of lactose and the sucrose omitted. The peptone provides the required carbon, nitrogen and vitamins. Lactose is a fermentable carbohydrate and di-potassium phosphate is a buffer. Eosin Y and methylene blue are indicators. Methylene blue is also a selective agent. During strong acidic conditions, the dyes impart a metallic sheen to certain lactose fermenters, such as Escherichia coli.  
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  • Tryptone water is recommended for the detection of Escherichia coli in food and water samples. Tryptone water is an alternative medium to peptone water and is more reliable for the testing of indole production. Tryptone acts as source of carbon, nitrogen and vitamins in this medium and sodium chloride maintains osmotic balance. The medium has a high content of tryptophan that many organisms, particularly coliforms, break down to form indole. After the recommended incubation indole positive organisms will give a distinct colour change when either Kovac’s or Ehrlich’s indole reagent is added.
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  • Mannitol Salt Agar is selective medium for the isolation of pathogenic staphylococci. The medium conforms to the requirements of the Harmonised USP/EP/JP. Chapman showed that adding a high level of sodium chloride to Phenol Red Mannitol Agar allowed for the recovery of pathogenic staphylococci. Pathogenic staphylococci produced yellow colonies whereas non-pathogenic staphylococci produced small red colonies. Pancreatic digest of casein, peptic digest of animal tissue and beef extract provide the required nitrogen, carbon and vitamins. The high level of sodium chloride inhibits most organisms other than staphylococci. Mannitol is a carbohydrate that is fermented by coagulase positive staphylococci. Phenol red is the pH indicator.
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  • Hektoen enteric agar was developed by King and Metzger as a differential selective medium for the isolation of Shigella spp. and Salmonella spp. species from enteric pathological samples. The meat peptone and yeast extract provide the required nitrogen, carbon and vitamins. Lactose, sucrose and salicin are fermentable carbohydrates. Bromothymol blue is added as a pH indicator in order to identify carbohydrate fermenting organisms. The combination of ferric ammonium citrate and sodium thiosulfate allows the production of hydrogen sulphide. Hydrogen sulphide positive colonies produce black centred colonies. Sodium chloride maintains the osmotic balance. The bile salts and acid fuchsin inhibit Gram-positive organisms.
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  • This is a selective medium for the isolation of Salmonella spp. and Shigella spp. from clinical specimens and food samples. SS agar is a modification of the original DCA medium described by Leifson. The formulation for SS agar was later modified to improve the growth of Shigella spp. SS agar modified differs from SS agar in that it has an alternation to the bile salts mixture, peptone, pH value, and total g/litre. The peptone provides the required carbon, nitrogen and vitamins. Lactose is a fermentable carbohydrate and neutral red is a pH indicator. Sodium thiosulphate and ferric citrate are used to detect hydrogen sulphide production indicated by the black centred colonies of hydrogen sulphite positive organisms. Bile salts, sodium citrate and brilliant green inhibit Gram-positive bacteria and a number of different coliform bacteria.
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