Determinative Schemes
- culture characteristics
- microscopic examination
- biochemical analysis
Culture Characteristics
tells what the organism needs to grow
Microscopic Examination
will evaluate the species’ morphology, arrangements, and specialized structures
Biochemical Analysis
determines which enzymes the organism makes and which abilities it has.
Enzymes
- are proteins that speed up chemical reactions
- made by bacteria that fall into two classes: endoenzymes and exoenzymes.
Endoenzymes
made inside the bacterial cell and work within the bacterial cell.
Exoenzyme
- enzymes that are made inside the
bacteria cell, but are then released by the cell to work outside the cell. - One function of an exoenzyme might be to break up large molecules outside the cell that would otherwise not be able to enter the cell.
Beta (β) hemolysis
the bacteria completely break apart the red blood cells, leaving a clear area around the growth.
Alpha (α) hemolysis
- is when the bacteria only PARTLY damages the red blood cells
- which makes the area look greenish or brownish.
Gamma (γ) hemolysis
- there is no damage
- so the area around the growth doesn’t change.
Sheep’s Blood Agar (SBA)
helps tell which kind of hemolysis the bacteria can perform through the color change in the agar .
- Beta (β) = clear
- Alpha (α) = green/brown
- Gamma (γ) = no change.
Hemolysins
- Some types of Gram-positive cocci bacteria make special enzymes called hemolysins.
- These enzymes can break open red blood cells and destroy hemoglobin, the protein that carries oxygen in our blood.
Carbohydrate fermentation
- is the metabolic process in which
bacteria uses carbohydrates to generate energy as adenosine triphosphate (ATP). - this process can create different waste products, such as acids or gases.
Phenol Red Broth (PRB)
- It contains one specific sugar (like glucose, lactose, or sucrose) and a pH indicator called phenol red, which changes color depending on whether the medium is acidic or basic.
- Red or orange = neutral (no fermentation)
- Yellow = acidic, meaning the bacteria can ferment the sugar
- Fuchsia (pink) = basic, meaning the bacteria cannot ferment the sugar and instead use the proteins (peptones) in the medium
Durham tube
gas detector
- a small upside-down glass tube placed inside a test tube of Phenol Red Broth (PRB)
- It’s used to catch gas that bacteria might produce during fermentation.
- If there’s no bubble, the bacteria did not produce gas.
- If there’s a bubble in the tube, the bacteria did produce gas during fermentation.
hydrogen peroxide
When bacteria use oxygen to make energy, they sometimes create a harmful chemical
catalase
Some bacteria can protect themselves by making an enzyme called catalase, which breaks hydrogen peroxide down into water and oxygen so it doesn’t damage the cell.
To see if bacteria makes catalase, scientists add hydrogen peroxide to a sample of the bacteria:
If bubbles form, oxygen is being released — the bacteria are catalase positive.
If no bubbles appear, the bacteria are catalase negative (they don’t produce the enzyme).
