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Infectious Agents > Lab Quiz: Lab 3 > Flashcards

Lab Quiz: Lab 3 Flashcards

1
Q

What is the reaction that the enzyme catalase catalyzes in the catalase test?

A

2 H2O2 + catalase ——-> 2 H2O + O2 (bubbles)

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2
Q

What does the catalase test aid in?

A

Distinguishing between streptococci (neg) and staphylococci (pos) and is helpful in identifying other species of bacteria

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3
Q

What signifies a positive catalase test?

A

The formation of gas bubbles

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4
Q

What is the method of a catalase test?

A

Place a drop of hydrogen peroxide on a slide and using loop or needle obtain some growth from a plate and place it in the hydrogen peroxide

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5
Q

What are the 2 types of coagulase test?

A

Slide coagulase test (cell bound coagulase)

Tube coagulase test (cell free coagulase)

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6
Q

What happens in a positive tube coagulase test?

A

Gelling occurs

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7
Q

What happens in a positive slide coagulase test?

A

Fibrin forms and clings to the suspended bacteria which results in their sticking together

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8
Q

Which plasma gives the best result in a coagulase test, rabbit or human?

A

Rabbit

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9
Q

What is the procedure of a cytochrome c oxidase test?

A

Rub a lapful of growth from agar culture on filter paper containing oxidase reagent or then impregnate the filter paper with the reagent

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10
Q

What are the results of cytochrome c oxidase test?

A

Positive: dark purple within 30 seconds
Negative: yellowish reaction or delayed reaction of purple (more than 30 seconds)

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11
Q

What is the reagent specific for cytochrome c oxidase test?

A

N, N, N1, N1 - tetramethyl-p-phenylene-diamine dihydrochloride

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12
Q

What is added as an antioxidant in cytochrome c oxidase test?

A

Ascorbic acid

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13
Q

What is cytochrome oxidase c a part of?

A

The oxidative phosphorylation pathway

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14
Q

What are the different chemicals used in triple sugar iron (TSI) agar test?

A 
Dextrose (1 part)
Lactose (10 parts)
Sucrose (10 parts)
FeSO4
Phenol red
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15
Q

How do you read results when interpreting a TSI agar test?

A

Slant over base reaction, then record +/- gas, +/- H2S

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16
Q

How do you know if the substance is alkaline (K) with TSI?

A

Red

17
Q

How do you know if the substance is acidic (A) with TSI?

A

Yellow

18
Q

How do you know if there is gas (G) with TSI?

A

Bubbles or fracturing of media

19
Q

How do you know if the substance is H2S positive with TSI?

A

Presence of black precipitant in agar

20
Q

What is TSI used for?

A

Presumptive identification of the gram negative rods and the basis for additional tests

21
Q

How do you do TSI?

A

Stab base and streak slant with inoculating needle. Leave tube cap slightly loose. Incubate at 37ºC

22
Q

What does it mean if TSI is orange-red?

A

Uninoculated

23
Q

What does it mean if TSI is yellow (acid)?

A

Glucose and/or sucrose and/or lactose fermented

24
Q

What does it mean if TSI is red (alkaline)?

A

Glucose, sucrose, and lactose not fermented or exhausted

25
Q

What does it mean if TSI has blackening in the base?

A

H2S produced

26
Q

What does it mean if TSI has gas bubbles in base?

A

Aeroginc (gas producing) organism

27
Q

What does lesser amount of glucose compared to sucrose and lactose make possible with TSI?

A

The recognition of organisms with different fermentation paterns

28
Q

What does iron do in TSI?

A

Traps the H2S produced from the sulfur containing precursors to form black iron sulfide and gas produced in the depths of the agar shows up as bubbles or disruption of the agar

29
Q

When should TSI slants be read?

A

At 24 hours

30
Q

What happens if TSI slants have incubation periods that are too long?

A

Acid reactions may revert back to alkaline

The small amount of acid produced by glucose fermentation is oxidized which will remain or revert to alkaline

31
Q

What happens with TSI under low oxygen tension in the base?

A

The acid reaction de to glucose is maintained

32
Q

What is alkaline substances evolving due partly to?

A

The exhaustion of fermentable carbohydrates and the subsequent attack on peptones

Infectious Agents (38 decks)

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