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POM 4 Immunology > 4.4 Diagnostic Bacteriology > Flashcards

4.4 Diagnostic Bacteriology Flashcards

1
Q

What are the five types of infection?

A 
Bacteria
Fungi
Viruses
Protozo
Helminth Worms
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2
Q

What colour does gram positive bacteria stain?

A

Purple

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3
Q

What is the cell wall of a gram positive bacteria?

A

Thick peptidoglycan cell wall

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4
Q

What colour does gram negative bacteria stain?

A

Pink

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5
Q

What is the cell wall of gram negative bacteria like?

A

Two outer membranes with a thin peptidoglycan cell wall between it

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6
Q

What part of the bacterial cell wall “holds” the stain?

A

The peptidoglycan

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7
Q

In what order are the gram stain substances applied?

A

Crystal Violet
Iodine
Alcohol
Safranin

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8
Q

How do gram positive bacteria stain purple?

A

Crystal violet is held by the peptidoglycan layers

Alcohol dehydrates the peptidoglycan and tightens it, and since there are many peptidoglycan layers, the crystal violet cannot be washed out

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9
Q

How do gram negative bacteria stain pink?

A

After the alcohol has washed all the crystal violet out, safranin is added which stains any remaining bacteria pink

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10
Q

What does the shape coccus describe?

A

Sphere

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11
Q

What does the term bacillus describe?

A

Rod like

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12
Q

What shape can coccus bacteria sometimes form?

A

Groups / clusters like grapes

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13
Q

Describe the shape of diplococci

A

Spherical in pairs

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14
Q

What does staphylcocci look like?

A

Purple (gram positive), spherical in grape like clusters

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15
Q

What does streptococci look like?

A

Purple (gram positive), spherical in long chains

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16
Q

What does the hemolytic test do?

A

Tests capacity of bacteria to produce haemolysins which are enzymes that damage RBCs

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17
Q

What is gamma hemolysis?

A

No hemolysis therefore no yellow zone

18
Q

What is beta hemolysis?

A

Full hemolysis therefore fully transparent / yellow zone

19
Q

What is alpha hemolysis?

A

Partial hemolysis, therefore more opaque yellow / green area

20
Q

What medium is the hemolytic test conducted on?

A

medium containing sheep red blood cells

21
Q

What is the hemolytic test useful for differetiating between?

A

Staph, Strep and enterococcus

22
Q

What type of hemolysis producing greening?

A

Alpha

23
Q

What is the major cause of haemolysis in new born babies?

A

Group B Streptococcus or Streptococcus agalactiae is the commonest cause of meningitis in babies under 3 months

24
Q

What type of agar is used for the lactose fermentation test?

A

MacConkey Agar

25
Q

What does the MacConkey Agar contain?

A

Bile salts, crystal violet and lactose

26
Q

What colour does lactase positive bacteria show as?

A

Pink – this is because they are lactose fermenting which produces lactic acid, lowers the pH and therefore forms pink colonies

27
Q

What colour does lactase negative bacteria appear as?

A

Yellow/colourless colonies

28
Q

Which type of gram (negative or positive) is the lactose fermentation test used to differentiate between?

A

Negative

29
Q

What test is used to differentiate initially between types of gram positive bacteria?

A

Catalase test

30
Q

What will be seen in catalase positive bacteria?

A

Bubbles of oxygen

31
Q

What will be seen in catalase negative bacteria?

A

No bubbles

32
Q

What does catalase do?

A

Breaks down hydrogen peroxide

33
Q

What test is used to differentiate between different catalase positive bacteria?

A

Coagulase test

34
Q

What will be seen in coagulase positive bacteria?

A

Clumps

35
Q

What will be seen in coagulase negative bacteria?

A

No clumps

36
Q

How is the coagulase test conducted?

A

Add bacteria and plasma together

37
Q

How do clumps form in the coagulase test?

A

Coagulase catalyses prothrombin to thrombin which causes fibrinogen to be cross linked, resulting in fibrin which forms a clot

38
Q

How does the antibiotic susceptibility test show resistance?

A

There will be no zone of inhibition

39
Q

What does a larger zone of inhibition suggest?

A

A more successful antibiotic as it has killed more bacteria

40
Q

Which bacteria is gram positive, catalase positive and coagulase positive?

A

Staphylococcus aureus

POM 4 Immunology (14 decks)

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