unit 4 - biochemical methods / identification of bacteria

list biochemical methods to identify bacterial types

1. testing oxygen tolerance

2. testing fermentation

3. gelatinase test

4. deamination test

5. urease test

2 ways bacteria vary regarding oxygen

• oxygen use

• tolerance of oxygen in their environment

5 patterns of bacterial growth in an oxygen-free medium

• obligate aerobes

• obligate anaerobes

• facultative anaerobes

• aerotolerant anaerobes

• microaerophiles

describe the appearance of the 5 bacterial growth patterns in the oxygen-free medium (use diagram to draw if helpful)

obligate aerobe

obligate anaerobe

facultative anaerobe

can generate energy and grow in both presence and absence of oxygen

aerotolerant anaerobes

microaerophile

fermentation test

helps to identify bacterial type by showing the breakdown of carbohydrates to make ATP when oxygen is absent

2 ways results of fermentation tests are visualized

1. pH indicator - phenol red

   1. neutral pH = red colour

   2. acidic pH = yellow colour

2. inverted tube

   1. detects gas formation

identify which has undergone fermentation and which has not

gelatinase test

identifying bacterial type by testing whether organism can use proteins (extracellular proteases)

what occurs in a gelatinase test when the bacteria is protease-positive?

gelatin medium is liquified due to the bacteria having extracellular protease proteins

deamination test

identifies bacterial type by testing if an organism can use amino acids

what occurs in a deamination test when the organism can use amino acids?

when bacteria metabolize amino acids, ammonia (NH3) is released, which has a basic pH → pH indicator turns magenta

urease test

identifying bacteria by testing whether the organism can use urea

what occurs in a deamination test when the organism can use urea?

when bacteria metabolize urea, ammonia (NH3) is released, which has a basic pH → pH indicator turns magenta

how can we use a species’ classifications to identify unknown bacterial samples?

→ classifications are known for a species

→ unknown bacteria is subjected to multiple tests (positive or negative result)

→ results are compared with databases (bergey’s manual)

% of the test results that must match those of a given species when identifying bacteria

100%