Identification

Question 1

How should we go about identifying an unknown species?

Answer 1

1. Colony morphology
2. Gram status
3. Biochemical tests (if needed)

Question 2

What do we use to classify and identify bacteria?

Answer 2

Bergey’s Manual of determinative bacteriology

Question 3

What is the purpose of biochemical tests?

Answer 3

To further differentiate bacteria

Question 4

What is selective medium?

Answer 4

Allows the growth of certain types of microbes, while inhibiting the growth of others

Question 5

What is differential medium?

Answer 5

When specific microbes are present, the medium/bacterial colonies will exhibit a colour change. Providing information about the identity of the bacteria

Question 6

What is the use of MacConkey Agar?

Answer 6

To differentiate non-lactose fermenters and lactose fermenters
When bacteria colonies turn red, the bacteria is a lactose fermenter
When bacteria colonies do not turn red, the bacteria is a non-lactose fermenter

Crystal violet and Bile salt: selective for Gram-negative bacteria
Lactose and Neutral red: differentiate non-lactose fermenters and lactose fermenters

Question 7

What is the use of Mannitol Salt Agar?

Answer 7

To differentiate between non-mannitol and mannitol fermenters
When bacteria colonies turn yellow, that means that the bacteria is a mannitol fermenter
When bacteria colonies do not turn yellow, that means that the bacteria is a non-mannitol fermenter

High salt: selective for Staphylococcus spp
Phenol red and mannitol: Differentiate non-mannitol fermenters and mannitol fermenters

Question 8

What is the use of Blood Agar?

Answer 8

To determine the hemolytic properties of bacteria
Beta-haemolysis:
clear zone surrounds the colony
bacteria is able to produce toxic by-products which can destroy red blood cells

Alpha-haemolysis:
green/brown discolouration in the medium
reduction of haemoglobin in the red blood cells to methemoglobin in surrounding the bacterial colony occurs

Gamma-haemolysis:
no clearing occurs
no hemolysins are produced and red blood cell is not broken down

Protein source: provide nutrients
5% sheep blood: supports the growth of most bacteria and differentiate between hemolytic and non-hemolytic bacteria

Question 9

What is the importance of classifying bacteria?

Answer 9

help clinical microbiologists to differentiate microorganisms
identification of microorganisms quickly through colony morphology and gram status
organization of information from various researchers worldwide

Question 10

Match the tests results with the type of biochemical tests

1. purple/blue (positive)
2. bubbles appear (positive)
3. turn from green to blue (positive)
4. bright pink on the top layer (positive)
5. bright pink/cherry red (positive)
6. yellow (positive)
7. colonies turn red

Answer 10

1. oxidase test
2. catalase test
3. citrate test
4. indole test
5. PYR test
6. carbohydrate fermentation
7. lactose fermentation