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microbiology lab > Gram-Negative Identification > Flashcards

Gram-Negative Identification Flashcards

1
Q

What are the ingredients in the TSI slant?

A

0.1% glucose, 1% sucrose, 1.0% lactose, phenol red, peptones

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2
Q

What does it look like/mean when a TSI slant has an acid slant/acid butt?

A

Glucose fermentation plus lactose and or sucrose fermentation. Yellow slant and butt

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3
Q

What does it look like/mean when a TSI slant has an alkaline slant/alkaline butt?

A

No carbohydrate fermentation, peptones catabolized resulting in an alkaline pH due to ammonia production. Red slant and butt

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4
Q

What does it look like/mean when a TSI slant has an alkaline slant/acid butt?

A

Only glucose fermentation has occurred. Red slant, yellow butt

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5
Q

What does it look like/mean when a TSI slant has gas production?

A

Production of gas during fermentation occurred. Bubbles or cracks throughout the media

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6
Q

What does it look like/mean when a TSI slant has hydrogen sulfide production?

A

Hydrogen sulfide production has occurred. Black precipitate in tube

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7
Q

What other two types of media can be used to test for hydrogen sulfide production?

A

SIM agar and BEA

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8
Q

What is an organism that is positive for hydrogen sulfide production?

A

P. vulgaris

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9
Q

What is an organism that is negative for hydrogen sulfide production?

A

E. Coli

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10
Q

What is the name of the enzyme that can hydrolyze urea?

A

Urease

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11
Q

What are the end products of urea hydrolysis?

A

Ammonia, CO2, and water

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12
Q

What is the pH indicator in urea broth?

A

phenol red

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13
Q

What does a positive urease test look like?

A

Hot pink

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14
Q

What does a negative urease test look like?

A

No color change

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15
Q

What is an organism that is urease-positive?

A

St. epidermidis

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16
Q

What is an organism that is urease-negative?

A

E.coli

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17
Q

What are the components of SIM agar? What 3 things does SIM agar test for?

A

Peptones from casein, ammonium citrate, and sodium thiosulfate

It tests for hydrogen sulfide production, indole production, and motility

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18
Q

What must be added to the SIM deep following incubation to perform this test?

A

Kovac’s reagent

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19
Q

What does a positive result for a SIM deep look like?

A

H2s production - black precipitate
Indole production - red coloration
Motility - diffused growth from the initial stab line

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20
Q

What does a negative result for a SIM deep look like?

A

No color changes, straight stab line

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21
Q

What is the MRVP test?

A

Methyl Red Voges Proskauer test which tests for organisms that ferment glucose to form a mixture of fermentation acids

22
Q

What are the components of the MRVP broth and the purpose of each component?

A

The Methyl Red (MR) and Vogues Proskauer (VP) test. The purpose is to determine if the organism can ferment glucose and what types of fermentation acids are produced

23
Q

What reagent is added for the MR test?

A

Methyl Red

24
Q

What reagents are added for the VP test?

A

Barritt’s Reagent A (alpha-naphthol) and Barritt’s Reagent B (40% KOH)

25
Q

Can an organism be positive for both MR and VP?

A

No

26
Q

What is an organism that is MR-positive? What does this mean?

A

E.coli

27
Q

What is an organism that VP-positive? What does this mean?

A

Klebsiella pneumoniae

28
Q

What two organisms was the MRVP test originally designed to distinguish between?

A

E. coli and Enterobacter aerogenes

29
Q

What is the purpose of the citrate test?

A

To test if an organism can use citrate as a carbon source

30
Q

What ingredients are in the citrate agar slant?

A

Sodium citrate, bromthymol blue, sodium, and water

31
Q

What does a positive citrate test look like? What organism yields this result?

A

“Prussian blue” in color, Klebsiella pneumonia

32
Q

What organism would yield a negative citrate test?

A

E.coli

33
Q

What ingredients are in nitrate broth? Is this an aerobic or anaerobic process?

A

Beef extract, peptone, and nitrate. Anaerobic

34
Q

What reagents need to be added to the nitrate broth following incubation?

A

Nitrate reagents A and B and zinc

35
Q

What does a positive result following the addition of these reagents mean? When would you need to add zinc to the tube?

A

Nitrate has been reduced to nitrite. If no red color is produced, add zinc

36
Q

What does a “positive” result following the addition of zinc mean?

A

The zinc reduced the nitrate to nitrite

37
Q

What does a “negative” result following the addition of zinc mean?

A

Nitrate has been fully reduced to nitrite

38
Q

What is an organism that is positive for nitrate reduction?

A

B. cereus

39
Q

What is an organism that is negative for nitrate reduction?

A

M. bovis

40
Q

What are the ingredients in LIA slants and what two biochemical reactions do these slants test for?

A

Lysine, glucose, peptones, bromcresol purple, sodium thiosulfate, and ferric ammonium citrate. These slants test for Lysin deamination (slant) and Lysine decarboxylation (butt)

41
Q

Which reaction is aerobic and which is anaerobic in an LIA slant?

A

Deamination is aerobic and decarboxylation is anaerobic

42
Q

What does it mean when an LIA slant has a purple butt?

A

Positive lysine decarboxylation

43
Q

What does it mean when an LIA slant has a yellow butt?

A

negative lysine decarboxylation

44
Q

What does it mean when an LIA slant has a purple slant?

A

Negative lysine deamination

45
Q

What does it mean when an LIA slant has a red slant?

A

positive lysine deamination

46
Q

What does it mean when an LIA slant has a black precipitate?

A

Hydrogen sulfide was produced

47
Q

What ingredients in MacConkey agar are differential and what do they differentiate?

A

Lactose, lactose fermentation

48
Q

What ingredients in MacConkey agar are selective and what do they select for?

A

Bile salts and crystal violet, Gram-negative bacteria

49
Q

What is an organism that can ferment lactose?

A

E. Coli

50
Q

What is an organism that cannot ferment lactose?

A

S. typhimurium

microbiology lab (7 decks)

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