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MBIO 345 > Module 8 > Flashcards

Module 8 Flashcards

1
Q

What is the catalase test useful in?

A

Differentiates Staph from Strep

Myobacterium species ID

Anaerobe ID

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2
Q

What is a positive test for catalase?

A

Bubble formation

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3
Q

What percentage of H2O2 is used?

A

3% from 30%

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4
Q

How is H2O2 stored and why?

A

Brown/amber bottle to prevent breakdown by light.

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5
Q

What is the rapid tube method catalase test?

A

Negative control- stick in H2O2

Pick colonies and immerse in tube with 0.5mL

Observe for bubbles

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6
Q

What is the rapid slide catalase test?

A

Negative control

Place drop of reagent on slide

Pick up colonies and immerse

Observe for bubbles

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7
Q

What is the overnight culture catalase method?

A

Pour 1mL reagent over 24hr growth on plate

Observe for bubbles

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8
Q

Why should platinum wire not be used for catalase tests?

A

May cause H2O2 breakdown, false positive reaction.

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9
Q

Why can blood alter catalase results?

A

It contains catalase and can therefore cause false positives.

If blood agar is picked up the results can be false.

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10
Q

Why should old cultures not be used for catalase testing?

A

Can lose their catalase catalase activity, gives false negatives.

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11
Q

What are the controls for the catalase test?

A

Positive- any Staph specie

Negative- any Strep species or stick

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12
Q

What does the nitrate reduction test determine?

A

Whether an organism to reduce the nitrate.

Previously used as a Staph genus test.

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13
Q

What can the nitrate reduction test ID?

A

Enteriobacteriaceae

Nonfermentative gram negative bacilli

Separation of Staph and Strep

Anaerobes

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14
Q

How is the nitrate reduction test complicated?

A

A variety of end products can be produced, detection can be difficult.

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15
Q

What are the end products of the nitrate reduction test? How are they detected?

A

Nitrogen gas- accumulates in Durham tube (not Staph)

Add reagents if no gas formed

Nitrite- red colour, Staph species

No red, add Zn

Unreduced nitrate to nitrite- red colour

Other endproducts- no red colour, not Staph

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16
Q

What medium is used for the nitrate reduction test?

A

Nitrate medium- beef extract, peptone, potassium nitrate

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17
Q

What reagents are used in nitrate reduction tests?

A

A- sulfanic acid in acetic acid

B- alpha naphthylamine in acetic acid

Zn

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18
Q

What quality control is performed in the nitrate reduction test?

A

Medium tested for the presence of nitrate- add A, B and Zn, if red colour nitrate is in medium

Positive control- S. aureus

Negative control- Strep species

19
Q

What does the coagulase test detect?

A

The presence of catalase enzyme.

20
Q

What are the different types of coagulase enzyme?

A

Bound/clumping factor- part of cell wall, acts on fibrinogen to form fibrin, detected with slide test

Free- extra cellular enzyme, produces thrombin-like substance, converted to fibrin clot, detected with tube test

21
Q

What is the reagent for coagulase tests?

A

Lyophylized human or rabbit plasma.

22
Q

What anticoagulant is used for coagulase tests?

A

Heparin or EDTA

23
Q

Why is citrate not used for coagulase tests?

A

Some bacteria use citrate.

Can give false positive results.

24
Q

How is the slide coagulase test performed?

A

Drop of saline on slide

Emulsify several colonies

Stir in loop full of plasma

Observe for clumping or agglutination

25
Q

Why should a weak bacterial suspension not be used for coagulation tests?

A

Can give false negatives.

26
Q

How is the tube coagulase test performed?

A

0.5mL of plasma in tube

Emulsify colony portion

Incubate at 35°C for 4hrs

If negative incubate at room temp for 24hrs

Observe for full or partial clot

27
Q

What can alter the results of a coagulase test?

A

Temperature >35°C can prevent formation (some S. aureus)- false negative

Frequent and excess agitation prevents formation- false negative

> 24hr incubation- S. aureus produces staphylokinase that can dissolve clots, false negative

Serum- false positive

28
Q

What are the controls used for coagulase testing?

A

Positive- S. aureus

Negative- S. epidermidis

29
Q

What does the DNase test detect?

A

Whether the bacteria produces enzymes that will depolymerize or unwind DNA.

30
Q

What are the applications of DNase testing?

A

S. aureus from other Staph

Moraxella catarrhais from Neisseria species

Serratia species from other Enterobacteriaceae

Xanthomonas maltophilia from other nonfermentative gram negative rods

31
Q

What are the three indicator systems for DNase testing?

A

HCl acid

Methyl green

Toluidine blue

32
Q

How is HCl acid used to determine DNase presence?

A

Plate with DNA is inoculated and incubated overnight

Flooded with HCl

Positive- clear zones, oligonucleotides are soluble in HCl

Negative- precipitate around growth, while DNA precipitated by the acid

33
Q

How is methyl green used to determine DNase presence?

A

Inoculate methyl green DNase agar

Incubate

Positive- clear zones, oligonucleotides make the solution colourless

Negative- green up to growth, while DNA bound is green

34
Q

How is toluidine blue used to determine DNase presence?

A

Inoculate DNase agar

Incubate overnight

Flood with 0.1% toluidine blue dye

Positive- pink colour in the presence of oligonucleotides

Negative- blue colour in the presence of whole DNA

35
Q

What are the controls used for DNase tests?

A

Positive- S. aureus, Serratia marcescens

Negative- S. epidermidis, E. coli

36
Q

What does the B-lactamase test detect?

A

The presence of B-lactamase enzymes which can inactivate penicillins and cephalosporins.

37
Q

Where is bacteria scraped from for B-lactamase testing?

A

The zone of inhibition.

38
Q

How can the production of B-lactamase be induced?

A

Growing the organism in the presence of a B-lactam antibiotic.

39
Q

What are the three methods for detection of B-lactamase?

A

Acidimetric method

Iodometric method

Chromogenic cephalosporin test

40
Q

How does the acidimetric method detect B-lactamase?

A

Hydrolysis of the B-lactam ring yields an acidic pH that can be detected.

Growth is rubbed on a moistened strip of benzylpenicillin with indicator.

Colour change indicates bacteria.

30 min.

41
Q

How does the iodometric method detect B-lactamase?

A

When penicillin is hydrolyzed to penicilloic acid iodine is converted to iodide, purple colour is lost.

Filter paper soaked in antibiotic, starch and iodine has colonies rubbed on.

Clear area indicates presence of the enzyme.

30 min.

42
Q

How does the chromogenic cephalosporin test detect B-lactamase?

A

Uses nitrocefin which changes from red to yellow when hydrolyzed.

Strip/disc is moistened and bacterial colonies are added.

Yellow to red indicates a positive test.

15 min.

Discs are light sensitive.

43
Q

What does the catalase test detect?

A

Detects the catalase enzyme that causes the breakdown of H2O2.

Genus test (Staph vs Strep).

MBIO 345 (11 decks)

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