S-S agar (Salmon, Shigella spp. agar) is a selective medium with a strong inhibitory effect on E. coli and no inhibitory effect on enteric pathogens; therefore, it can increase the inoculum of specimens and improve the positive isolation rate of enteric pathogens.

Operation method

devote one's energies to a flatbed

Principle

1. Neutral red is an indicator, it is red in acidity and light yellow in alkalinity, general intestinal pathogenic bacteria do not decompose lactose, but decompose peptone, which produces alkaline substance, so the colony is light yellow. 2. E. coli ferment lactose, acid production makes the indicator red, so the colonies are red, neutral red can be destroyed by light, the medium should be kept in the dark. 2. sodium citrate and brilliant green can inhibit the growth of E. coli, sodium citrate does not inhibit enteropathogenic bacteria. Both Brilliant Green and Neutral Red are toxic to bacteria. Sodium thiosulfate neutralizes the toxicity of Neutral Red and Brilliant Green and sharpens the color of red colonies of E. coli. Iron citrate can also neutralize the toxic effects of neutral red and brilliant green. When bile salts are used in combination with sodium citrate and sodium thiosulfate, they can enhance the bacteriostatic effect on E. coli, and bile salts can promote the growth of Salmonella.

Materials and Instruments

Paste liquid agar; lactose; sodium citrate; sodium thiosulfate; ferric citrate solution; neutral red aqueous solution; brilliant green aqueous solution; bile salts

Move

Heat to dissolve the sterilized meat paste liquid agar, then add lactose, sodium citrate, sodium thiosulfate, bile salts, iron citrate, so that it is all dissolved while hot, correct the pH to 7.0 -7.2, filtration, and make up for the loss of water, and continue to boil for 10 minutes, then add Brilliant Green, Neutral Red solution, shaking well, poured into the sterilized flat dish.

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