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POM IMMUNOLOGY > Diagnostic Bacteriology > Flashcards

Diagnostic Bacteriology Flashcards

1
Q

What are the five types of infection?

A

Bacteria
Fungi
Viruses
Protozoa
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 are the different shapes of bacteria?

A

coccobacilli, bacilli, diplococci

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11
Q

What does the shape coccus describe?

A

Sphere

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12
Q

What does the term bacillus describe?

A

The rounded oval shape/ rod-like

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13
Q

What shape can coccus bacteria sometimes form?

A

Groups / clusters like grapes

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14
Q

Describe the shape of diplococci

A

Spherical in pairs

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15
Q

What does staphylcocci look like

A

Purple, spherical in grape like clusters

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16
Q

What does streptococci look like?

A

Purple, spherical in long chains

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17
Q

What does the hemolytic test do?

A

tests capacity of bacteria to produce hemolysins which are enzymes that damage RBCs

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18
Q

How do you carry out the haemolytic test?

A

samples are grown overnight on blood agar plates

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19
Q

What is gamma hemolysis?

A

No hemolysis around the colonies therefore no yellow zone

20
Q

What is beta hemolysis?

A

Full hemolysis therefore large clear zone of haemolysis around the bacterial colonies

21
Q

What is alpha hemolysis?

A

Partial hemolysis, therefore colonies appear more green

22
Q

What medium is the hemolytic test conducted on?

A

medium containing sheep red blood cells

23
Q

What type of hemolysis producing greening?

A

Alpha

24
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

25
Q

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

A

MacConkey Agar

26
Q

What does the MacConkey Agar contain?

A

bile salts, crystal violet and lactose

27
Q

What colour does lactase positive bacteria show as?

A

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

28
Q

What colour does lactase negative/ lactose non-fermenter bacteria appear as?

A

Yellow/colourless colonies

29
Q

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

A

Negative

30
Q

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

A

Catalase Test

31
Q

What will be seen in catalase positive bacteria?

A

Bubbles of oxygen

32
Q

What will be seen in catalase negative bacteria?

A

No bubbles

33
Q

What does catalase do?

A

Breaks down hydrogen peroxide

34
Q

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

A

Coagulase test

35
Q

What will be seen in coagulase positive bacteria?

A

Clumps

36
Q

What will be seen in coagulase negative bacteria?

A

No clumps

37
Q

How is the coagulase test conducted?

A

Add bacteria and plasma together

38
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

39
Q

How does the antibiotic susceptibility test show resistance?

A

There will be no zone of inhibition

40
Q

What does a larger zone of inhibition suggest?

A

A more successful antibiotic as it has killed more bacteria

41
Q

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

A

Staphylococcus aureus

42
Q

How do you carry out the haemolytic test?

A

samples are grown overnight on blood agar plates

43
Q

What are 4 different growth mediums for bacteria?

A

Nutrient agar, blood agar, MacConkey agar, Diagnostic sensitivity test agar (DST)

44
Q

What is nutrient agar?

A

A simple medium used to grow bacteria. usually contains peptone, meat extract, and sodium chloride plus agar.

45
Q

What is blood agar?

A

Nutrient agar base with sterile blood (either horse or sheep) added. This medium is suitable for testing for haemolysis (the destruction of red blood cells). Haemolysis is important for diagnosing certain microorganisms.

46
Q

what is macconkey agar?

A

A selective media used to isolate coliforms and intestinal pathogens. It contains bile salts to inhibit the growth of non-intestinal pathogens. The media also contains lactose, peptone and the dye neutral red. Neutral red acts as a pH indicator; when the pH is acidic (< pH 6.8) it turns red/pink and when the pH is basic (> pH 8) it turns yellow.

MacConkey agar is commonly used to determine lactose fermentation by bacteria. If the bacteria ferment lactose, then acid is produced as a by-product which decreases the pH of the media. If the bacteria are lactose non-fermenters then they use the peptone instead, then ammonia is formed as a by-product which increases the pH of the media.

47
Q

What is diagnostic sensitivity test agar?

A

A medium used for antibiotic sensitivity testing. None of the ingredients in the medium interfere with the action of the antibiotics and the agar base allows the diffusion of large molecule antibiotics.

POM IMMUNOLOGY (13 decks)

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