triple sugar iron agar

micro lab

purpose of TSIA

differentiate gram negative enteric bacteria based on glucose, lactose, and sucrose fermentation

pH indicator

phenol red

innoculation method

stab and streak

black precipitate meaning

indicates sulfur reduction and fermentation

hydrogen sulfide gas was produced by the reduction of thiosulfate or breakdown of cysteine in the peptone

ferrous sulfate reacts with H2S to form the precipitate

• salmonella typhimurium

incubation period

18-24 hours for carbohydrate fermentation

48 hours for H2S production

yellow medium

glucose-only fermentator was inoculated and lowered the pH

reversion

Glucose diminishes, organisms break down amino acids, produce NH3, and raise the pH

red slant, yellow butt

ferments glucose but not sucrose and lactose

yellow medium

ferments all sugars

red medium

organisms does not ferment any carbohydrates but does utilize peptone and amino acids

ferrous sulfate

reacts with H2S to form black precipitate

small amount of glucose because

allows for pH changes and different levels of fermentation with lactose and sucrose