Biochemical tests

Indirectly checking for the enzyme by directly looking for the presence of the product or the disappearance of the substrate. Enzyme profile of bacteria Each species has a unique set of enzymes. Therefore, the enzyme profile helps us to identify bacteria.

Giving the bacteria substrate. If the bacteria makes the enzyme, substrate is converted to products. Substrate is a substance with which the enzyme reacts.

Exoenzymes Enzymes produced in the cell and then released into the environment. Breakdown macromolecules into smaller molecules. Smaller molecule cross the plasma membrane and they are used by the cell for energy or to make structures of the cell.

Starch hydrolysis Starch – amylase –maltose Add iodine – indicator for starch Purple complex Medium becomes purple after the addition of iodine – starch is still in the medium. Bacteria did not use it. Bacteria is negative for starch hydrolysis.

Clear area around the growth after adding iodine. No starch in the medium. Bacteria broke down the starch in the medium. Bacteria are positive for starch hydrolysis.

Skim milk agar Casein – caseinase – amino acids Medium is cloudy – casein Once the casein is broken down clearing around the growth. B. subtilis – positive C. xerosis - negative

gelatin Gelatin – gelatinase – amino acids Gelatin is liquid – positive for gelatinase. P. aeruginosa Gelatin is solid – negative for gelatinase. E. coli

Spirit blue agar Triglyceride – lipase - glycerol + 3 fatty acids. Medium is cloudy because of the triglyceride. Clearing of the cloudiness around the growth. Positive for lipase – P. aeruginosa No clearing – negative for lipase E. coli

Fermentation tubes Sugar – glucose, lactose, sucrose pH indicator – phenol red Red – neutral Yellow acidic Fuchsia (hot, bight pink) – basic Durham tube – tiny upside down tube Gas collection