Triple sugar iron agar showing gas production with red slant and yellow butt. The organism cultured is -

Ans. is 'b' i.e., Shigella flexneri Triple sugar iron agari) Fermentation of dextrose (glucose), lactose and sucrose.ii) Production of H2S.* It is recommended for differentiation of enteric gram negative bacilli from clinical specimens, dairy samples and food products.* Contents of the medium arei) Enzymatic digest of casein and animal tissue.ii) Yeast enriched peptone.iii) Three sugars: Dextrose (glucose), lactose and sucrose.iv) Ferric ammonium citrate.v) Sodium chloride.vi) Sodium thiosulfate.vii) Phenol red.viii) Agar.* When carbohydrates are fermented, acid production is detected by the phenol red indicator, which is yellow in acid and red in alkaline conditions.* Sodium thiosulfate is reduced to hydrogen sulfide (H2S) and H2S reacts with an iron salt yielding typical black iron sulfide. Ferric ammonium citrate is hydrogen sulfide indicator.Results* Two areas of tube are examined : (i) Butt of the tube, and (ii) Slant of the tube.* An alkaline slant (red)- acid butt (yellow) indicates fermentation of dextrose (glucose) only - red /yellow. Examples are Proteus mirabilis, salmonella thyphimurium and shigella flexneri.* An acid slant (yellow) - acid butt (yellow) indicates fermentations of dextrose (glucose), lactose and/or sucrose - yellow/yellow. Example is E coli.* An alkaline slant (red) - alkaline butt (red) indicates no fermentation (non-fermenter) red/red. Example is Pseudomonas aeruginosa.* An alkaline precipitate in butt indicates H2S production. It is produced by Proteus mirabilis and Salmonella typhimurium.OrganismSlantButtGasH2SE coliAcidAcid+-Proteus mirabilisAlkalineAcid-+Pseudomonas aeruginosaAlkalineAlkaline--Salmonella typhimuriumAlkalineAcid+/-+Shigella flexneriAlkalineAcid+