Lab Exam Flashcards
What do molecular methods of microbial identification rely on
distinctive features microbial nucleic acids for identification
What does serological methods of microbial identification rely on
recognition of microbial features by antibody proteins; based on the use of blood serum
What can antibody-based methods of microbe recognize
individual features on microbial cells called antigens
What does mass spectroscopy methods identify microbes based on
most abundant proteins in the cells
What are tests that help identify chemoheterotrophic bacteria
gram stain
motility
oxygen relationship
glucose fermentation
catalase
oxidase
What does the glucose fermentation test detect
whether the microbe can grow in the medium and if it can ferment glucose
What does a tube of carbohydrate fermentation broth contain that is the target component of the medium
specific sugar as a potentially fermentable carbon and energy source
What does brom-cresol purple do in glucose fermentaiton broth
changes to a yellow color as a result of the considerable acid production from fermentative breakdown of the sugar
What percent of gas is considered a positive result
10
What does the nitrate reduction test detect
whether the microbe can grow on the medium supplied using anaerobic respiration with nitrate as the final electron acceptor
What is the target component in the medium for nitrate reduction test
potassium nitrate
With the use of a durham tube in the medium reduction of nitrate to _______ or _____________ can be detected
nitrite; nitrogen gas
What do you look for to observe reduction of nitrate to nitrogen gas
large bubble in durham tube
What is the complete reduction of nitrate to n gas
denitrification
To test for reduction of nitrate to nitrite what do you need to add to the test tube and mix? what do you look for upon mixing
nitrite reagents (sulfanilamid and N-ethylenediamine); pink or red color
If you see no red in the test of reduction from nitrate to nitrite what do you do
add a few more drops of each reagent, mix well, and observe again
How do we check for unreduced nitrate
adding a small amount of granulated zinc to any tube not showing a positive reaction for nitrite or gas
If nitrate is present what will it look like
be reduced by the zinc to nitrite which will react with the reagents already added forming a pink or red color so it is negative for the reaction
Motility test detects
microbes that are motile with flagella can usually swim through a semi-solid medium containing a small amount of agar
How much agar is in the motility test
0.4
What is the target in the medium for motility
agar
What does the catalase test for
enzyme catalase present
what does catalase do
breakdown of toxic hydrogen peroxide
What type of respiring microbes would possess catalase
stric aerobes or facultative anaerobes
What is the hydrogen peroxide breakdown
2H2O2 –> 2H2O + O2
Prior to catalase how are the grown
on a slant or plate of an al purpose medium
What percent of hydrogen peroxide is added for the catalase test
3-5%
What type of reaction is the oxidase test
colorimetric reaction
What is oxidase testing for
cytochrome C oxidase enzyme in the respiratory electron transport chain
what color will the plastic strips turn when the oxidase test is positive
purple
T/F you must look for an immediate response to the oxidase test
T
The enterobacteriaceae is a family of gram ______ __________
negative proteobacteria
All enteric are…
gram stain
shape
gram negative rods
When are enteric bacteria mistaken for cocci
in older cultures as cells shorten up to a coccobaccilus shape
All enteric are…
_______heterotroph
respiration
chemoorganoheterotrophic
true facultative anaerobes
Are enterics able to ferment glucose
yes
All enteric are…
catalase
oxidase
positive
negative
T/F most enteric are motile
T
The KIA test is used only for gram _____ bacteria mainly enterics and pseudomonas
negative
What is the purpose of KIA test
test fermentation of a major sugar (lactose) and a minor sugar (glucose) as well as production of hydrogen sulfide
What is the purpose of the methyl red test
the purpose of this test is to identify the end products from glucose fermentation
what does the voges proskauer test indicate
the neutral products formed by the butanediol
generally enterics are positive for the MR or the VP test but not
both
What is the color for MR test that is postive and what does it mean
red; mixed acid fermentation; pH has dropped and then remained below 4.4
What is the color for a negative MR test and what does it mean
yellow; indicative of butanediol fermentation; pH has dropped and then risen to 6.2 or above
What is the purpose of the simmons citrate test
test for the use of citrate as a carbon and energy source
What is the target component in the medium simmons citrate test
sodium citrate
If citrate has been used….
an alkaline reaction results and turns bright blue
What medium is known to give false positive when there is too-heavy innoculation
simmons citrate agar
what does emb agar inhibit
growth of gram positive bacteria due to eosin and methylene blue dyes
What gram bacteria is typically used on EMB
negative
Can EMB be used to identify lactose fermenting bacteria
yes
Is EMB both differential and selective
yes
What will a coli type look like on EMB
colonies appear dark, and have bright green metallic sheen if observed by reflected light
Why does a sheen result
rapid fermentation of lactose, causing a low pH to precipitate methylene bue
What will a aerogenes type look like on EMB
colonies appear less dark; normally light colored with mucoid rim surrounds a dark center
What do non lactose fermenting microbes look like on EMB
light
What is the purpose of the phenylaline test
test for the deamination of the AA phenylalanine
if phenylalanine deamination has taken place, the reagent will react with the phenyl pyruvic acid formed and turn what color
dark green
What does MIO test
motility
ability to produce indole
ability to decarboxylate ornithine
how do bacteria produce indole, pyruvic acid, and ammonia
produce the enzyme tryptophan’s and degrade tryptophan
What is in kovac’s reagent
p-dimethylaminobenzoladhyde, butanol, and hydrochloric acid
What color is produced in MIO when there is a reaction with indole
red color
indole is detected in MIO by its reaction
with the chemicals in kovac’s reagent
How to test for ornithine decarboxylation in MIO
observe the lower 3/4 (anaerobic region) of the medium for change in color of the pH indicator; growth must be present in this part of the tube
What color will be present in ornithine decarboxylation of MIO when there is a positive reaction
gray, blue, purple
decarboxylation of lysine, ornithine, and histidine will result in production of
cadaverine, putrescine, and histamine
What is a negative reaction for lysine decarboxylase broth
yellow color
What is a positive reaction for lysine decarboxylase and what it means
gray, blue, purple–alkaline product that neutralizes the acid produced from glucose fermentation
will a strict aerobe such as pseudomonas grow in decarboxylase control test
no it will remain purple
What does the lactose fermentation test detect
whether the microbe can grow in the medium; and if so, if it can ferment lactose
What is the target component in lactose fermentation broth
lactose
What color change occurs if the lactose fermentation broth is positive
purple to yellow
What do multitest systems provide savings in terms of
time and reagents used
What number of multi test identification is used for enteric bacteria
20E
If the methyl red results are yellow what does it mean
negative reaction and has butanediol fermentation
If the methyl red results are orange what does it mean
equivocal reaction
How long must MR test incubate
about 2 days
How long must KIA be incubated
24 hours only
What type of medium is EMB
differentail and selective
What is the selevtive part of EMB
eosin and methylene blue dyes
What is the differentail part of EMB
lactose
How long must you incubate EMB
only 24 hours
What type of lactose bacteria will look fisheye on EMB
aerogenes type
How do you innoculate the phenylalanine test
streak across top of the penylalanine agar slant only
What does a dark green color appearing on the slant of a phenylalalinine test mean
phenylalanine deamination has occurred the reagent will react with the phenylpyruvic acid formed
How do you inoculate the MIO agar
stab the medium about 3/4 the depth of the tube
What reagent must be added to the test tube to determine if phenylalnine deamination ahs occured
FeCl3
If the bottom 3/4 (anaerobic region) is yellow in the MIO what does it mean
glucose fermentation occured
To determine indole production in MIO what must be added
kovacs reagent
Where is it best to detect formation of highly alkaline diamine
anaerobic growth region of the medium
What type of microbe will not grow in the decarboxylase control test
pseudomonas–a strict aerobe
What does pseudomonas look like in the decarboxylase broth
purple
Define obligate aerobic
requires oxygen
Define microaerophile
requires low levels of oxygen
Define facultative respirer
can grow with or without oxygen
Define obligate anaerobic respirer
oxygen free
