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IMMUNO > Diagnostic Bacteriology > Flashcards

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

Explain fully how gram positive bacteria stains purple?

A

After the crystal violet stain has been applied, it is held by the peptidoglycan layers. Then iodine is added, and alcohol. The alcohol dehydrates the peptidoglycan so it tightens it, meaning in gram positive since there are alot of layers, the purple 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

The rounded oval shape

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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, spherical in grape like clusters

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15
Q

What does streptococci look like?

A

Purple, 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 positie, catalase positive and coagulase positive?

A

Staphylococcus aureus

IMMUNO (14 decks)

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