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Microbiology MLSC 1009 > Unit 4 Differential testing > Flashcards

Unit 4 Differential testing Flashcards

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1
Q

how is an octal profile generated

A

+ive test value of 1, 2, and 4 for 3 grouped tests. add only the positive numbers up generates 7 digit ID

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2
Q

result of +ive and -ive for methyl red (MR)

A

+ive is red indicates mixed acid fermentation less than pH 4.4
-ive is yellow pH greater than 6.0

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3
Q

3 rapid spot tests

A

catalase, oxidase and spot indole

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4
Q

appearance of +ive and -ive for catalase

A

+ive bubbling H2O2 react w/catalase to produce water and O2

-ive no bubbling

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5
Q

reason for false +ive for catalase

A

false +ive: nichrome from using loop (use wooden stick), RBC from agar has catalase, other enzymes break down catalase weak bubbling

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6
Q

reason for false -ive for catalase test

A

old cultures lose enzyme, too slow in adding reagent

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7
Q

appearance of +ive and -ive for oxidase (cytochrome)

A

+ive blue (oxidized)

-ive is colourless (reduced)

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8
Q

reason for false +ive for cytochrome oxidase test

A

false +ive: auto-oxidation after 10 secs, nichrome from using loop (use wooden stick)

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9
Q

reason for false -ive for cytochrome oxidase test

A

media w/nitrate, tellurite or fermentable CHO; don’t use growth w/MacConkey, more than 24 hrs old

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10
Q

why is the dye TMPD used for cytochrome oxidase

A

acts as redox indicator, gives e-

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11
Q

purpose of spot indole test

A

org break down tryptophan (casein peptone) resulting in production of indole, pyruvic acid and ammonia

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12
Q

appearance of +ive and -ive for spot indole

A

+ive blue/green

-ive no colour change

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13
Q

reason for false +ive spot indole test

A

mixed culture plates –> indole diffuses into culture. don’t trust if both are +ive

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14
Q

reason for false -ive spot indole test

A

if media has glucose, drops pH, may inhibit indole production.

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15
Q

practices to remember for indole test

A

media must supply tryptophan for testing, don’t use reagent if brown/signs of deterioration, avoid plates w/indicator dyes e.g. MAC

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16
Q

purpose of 6.5% salt tolerance test

A

most org, high [NaCl] interfere w/membrane permeability and osmotic eqbm

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17
Q

appearance of +ive and -ive for 6.5% NaCl test

A

+ive turbid

-ive not turbid

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18
Q

reason for false +ive 6.5% NaCl test

A

over-inoculation

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19
Q

principles of Adonitol test

A

adonitol added to phenol red broth (a complete medium w/o CHO). Fermentation of adonitol carried out by adonitol dehydrogenase forming acidic end products

20
Q

appearance of +ive and -ive for Adonitol test

A

+ive yellow or turbid

-ive red, no change, turbid

21
Q

what else can be added in Adonitol test and why

A

Durham tube checks gas production from fermentation. fastidious org +ive reactions is 3-5 days. 30 days to confirm -ive result. if org cannot grow in phenol red broth, turbidity not present

22
Q

principle for Bile Esculin Agar (BEA)

A

selective b/c 40% bile: inhibits gp except for enterococci and Group D streptococci. differential b/c esculin

23
Q

appearance of +ive and -ive for BEA

A

+ive translucent growth with blackening

-ive no growth/no blackening

24
Q

what is the indicator is BEA

A

Fe3+ (from the indicator ferric ammonium citrate). blackening of media

25
Q

notes to remember for BEA test

A

some staphylococci grow in presence of bile producing weak iron complex (black) growth is opaque on slant, -ive BEA. Listeria monocytogenes is +ive for esculin hydrolysis and may do so in presence of bile, thus important to do catalase and colony smear. BEA ≠ esculin test; the latter does NOT contain bile (is non-selective)

26
Q

principle of Citrate test

A

Simmons Citrate Agar contains ammonium dihydrogen phosphate, only source of nitrogen and sodium citrate, only source of carbon. org capable of using ammonium dihydrogen phosphate and citrate will grow

27
Q

appearance of +ive and -ive for citrate test

A

+ive Growth on the slant ** +/- blue colour

-ive: No growth on the slant, no colour change

28
Q

describe pH indicator of citrate test

A

Bromothymol blue causes medium to change from green (neutral) to blue (alkaline) with increasing pH (pH >7.6)

29
Q

notes to remember for citrate test

A

inoculating from broth culture and heavy inoculum= false positive results. org can grow on citrate medium but won’t produce a color change still +ive result. if screw cap used, loosen to provide aerobic condition

30
Q

principle of decarboxylase test (moeller’s method)

A

first fermentation of dextrose lower ph (purple to yellow) second decarboxylation of amine (yellow to purple)

31
Q

procedure of decarboxylase test

A

inoculate 3 broth: lysine, base and orthinine decarboxylase. added oil

32
Q

why results invalid if oil not added for decarboxylase test

A

air causes alkalinsation due to DEAMINATION of peptones

33
Q

what does MIL stand for

A

motility, indole and lysine

34
Q

MIL tests for what

A

H2S production, indole formation and motility of enteric org

35
Q

+ive and -ive test for sulfide

A

+ive blackening

-ive no change

36
Q

reagents of MIL

A

SIM medium w/o TTC (dye to determine motility) and Kovac’s reagent (indole test)

37
Q

purpose of TSI agar

A

diff of gnb on CHO utilization (oxidative or fermentative) and H2S production

38
Q

what is in TSI

A

peptones, CHO, sodium thiosulfate, ferrous NH4 sulfate, salt, 1.3% agar, phenol red

39
Q

principles of TSI

A

glucose fermented: pink on slant yellow butt (k/a)
if lactose or sucrose ferments: all yellow (ala)
nf gnb: k/nc
h2S blackening
fermentation causes gas bubbles

40
Q

urease test principles

A

for org hydrolyzing urea from ammonia turns medium alkaline. phenol red. yellow to red/pink

41
Q

+ive and -ive test for urease

A

phenol red
+ive pink
-ive no colour yellow

42
Q

false +ive of urease

A

utilization of peptones or proteins may pH to 7+ due to protein hydrolysis

43
Q

principle of MR/VP test

A

tests further fermentation of pyruvate. glucose fermentation

44
Q

+ive and -ive test for VP test

A

+ive red colour

-ive yellow rusty brown

45
Q

notes for MR/VP test

A

MR not preformed at BCIT (48hrs incubation)

Microbiology MLSC 1009 (13 decks)

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