Identification Flashcards

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1
Q

How should we go about identifying an unknown species?

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

What do we use to classify and identify bacteria?

A

Bergey’s Manual of determinative bacteriology

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3
Q

What is the purpose of biochemical tests?

A

To further differentiate bacteria

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4
Q

What is selective medium?

A

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

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5
Q

What is differential medium?

A

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

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6
Q

What is the use of MacConkey Agar?

A

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

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7
Q

What is the use of Mannitol Salt Agar?

A

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

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8
Q

What is the use of Blood Agar?

A

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

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9
Q

What is the importance of classifying bacteria?

A

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

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10
Q

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