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MBIO 360 > Module 8 > Flashcards

Module 8 Flashcards

1
Q

What is the basis for carbohydrate fermentation?

A

Acid formation is detected by pH indicators and indicates carbs have been fermented

Aerogenic vs anaerogenic

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2
Q

What pH indicators are used for carb fermentation?

A

Phenol red- red (k) and yellow (a)

Bromcresol purple- purple (k) and yellow (a)

Bromthymol blue- blue (k) and yellow (a)

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3
Q

What can cause erroneous results in carb fermentation?

A

Over incubation- reversion/false neg

Peptone utilization in oxygen- accumulation of alkaline products/false neg

Sterilization via heat

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4
Q

What is the basis for TSI testing?

A

Agar contains lactose, sucrose, glucose

Slanted media gives deep butt (oxygen free environment)

Loose caps for oxygen exposure on slant

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5
Q

How are TSI results interpreted?

A

K/A- ferments glucose, peptone metabolism in oxygen

A/A- lactose and/or sucrose

K/K, NC/NC- no fermentation

Aerogenic fermentation- split medium/bubbles

H2S- thiosulfate metabolism

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6
Q

What is KIA agar?

A

Same as TSA but without sucrose

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7
Q

What can cause false negatives in TSI?

A

Shallow butt

Tightly capped tube

Extended incubation (reversion)

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8
Q

What is the basis for ONPG testing?

A

Ability to ferment glucose

Substrate moves into cell without permease and is hydrolyzed to a yellow product (orthonitrophenol) and galactose if galactosidase is present

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9
Q

What enzymes are required for lactose fermentation?

A

Permease- moves lactose into cell

Galactosidase- hydrolyzes lactose

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10
Q

What are the categories of lactose fermentation and their ONPG reaction?

A

LF- both enzymes, pos

NLF- neither enzyme, neg

LLF- permease only induced by lactose, delayed, pos

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11
Q

What do LF look like on MAC?

A

Pink colonies

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12
Q

What is the basis for indole testing?

A

Determines ability to decompose tryptophan to indole using tryptophanase

Reagent reacts with indole to give red coloured product

Requires high tryptophan concentration

Most Enterobacteriaceae are positive

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13
Q

What are the types of indole testing?

A

Tube- Kovac’s reagent added to broth, pos = red, neg = yellow

Spot- rapid, growth add to filter paper with reagent, pos = blue-green or pink-lavender, neg = yellow-brown

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14
Q

What is the basis for Voges Proskauer (VP) testing?

A

Tests for the production of butylene glycol from carb metabolism

Detects intermediate product (acetoin)

Oxygen required

Neg- colourless/brown

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15
Q

What types of VP tests are there?

A

Methyl red- no longer used

Rapid- inoculum where fermentation has occurred is added to creatine solution followed by KOH and alpha naphthol, red = pos

Incubated- broth incubation, reagents added

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16
Q

What is the basis for citrate testing?

A

Determines whether citrate can be the sole use of carbon

Alkaline pH results in deep blue colour

Simmon’s citrate- bromthymol blue (neutral = k, blue = a)

17
Q

What causes false results in citrate?

A

Liquid medium- C and N carryover/false pos

Oil overlay- no oxygen/false neg

Not completely filled- false neg

18
Q

What is the basis of urease testing?

A

Determines ability to decompose urea to CO2 and NH3 using urease

Phenol red is pH indicator

Pos- alkaline pH, red

19
Q

What types of urease testing are there?

A

Broth- highly buffered, PO4 resist pH changes, less sensitive, oil overlay

Christensen’s agar- less PO4, more sensitive, glucose fermented by negative organisms (yellow)

20
Q

What is the basis for phenylalanine deaminase (PDA) testing?

A

Determines whether deaminase present to remove amino acid and give keto acid and NH3

Pos- acid detected by ferric chloride, dark green

Neg- ferric chloride gives yellow

Correlates with TDA

Commercial systems- deamination gives black colour

21
Q

What is the basis for decarboxylase testing?

A

Determines ability to remove carboxyl group from an amino acid using decarboxylase

Use lysine and ornithine

Miller medium- bromcresol purple and creosol red are pH indicators

Incubated free of oxygen (oil overlay)

Requires control without amino acid

22
Q

What are the results for decarboxylase testing?

A

Pos- acid from glucose fermentation promotes decarboxylation, alkaline amine neutralizes and accumulates, deep purple

Neg- ferments glucose, remains yellow, no neutralization

23
Q

What can cause false results in decarboxylase testing?

A

Over incubation- reversion/false pos

Oxygen- false pos

24
Q

What are conventional Enterobacteriaceae ID tests used for?

A

Screening isolates for enteric pathogens

Supplemental tests for commercial systems

Presumptive ID

MBIO 360 (14 decks)

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