Lab Final Flashcards
what is the most important nutrient for bacteria to have
carbon (autotroph versus heterotroph)
what influence does temperature have on bacterial growth
influences the rate of chemical reactions in the cell
what are the two main types of bacterial cultivation
defined media and complex media
how are defined media composed
composed of known quantities of chemically pure and specific organic/inorganic compounds. (very specific recipe)
what are two examples of defined media
inorganic synthetic broths or glucose salt broths
what are complex media
exact chemical composition not known. made from animal and plant tissue extracts.
what are two examples of complex media
nutrient broths and yeast extract broths
what is a nutrient broth made of
peptone and beef extract
what is yeast extract broth made of
nutrient broth (peptone and beef extract) plus yeast
what does turbidity indicate
bacterial growth
what are selective media
used to isolate specific groups of bacteria
how do selective media work
chemicals to inhibit growth of one organism but allows growth of another organism
what are three examples of selective media
phenylethyl alcohol (pea), crystal violet, sodium chloride
what are differential/selective media
will produce a change in appearance of bacterial growth on or around the colonies, and also can inhibit growth of some organisms
what are examples of differential/selective media
MSA, MacConkey’s, Eosin-methylene blue
how does MSA work
inhibits by salt concentration, mannitol (to ferment) and a pH indicator for detecting fermentation (yellow -)
how does macconkeys work
does not allow gram positive to grow, fermentation of lactose with ph indicator
how does eosin-methylene blue work
fermentation of lactose, doesnt grow gram positive
how does PEA work
(phenylethyl alcohol) only allows gram positive growth
what are enriched media
media with highly nutritious materials
what are some nutrients used in enriched media
blood, serum, yeast
how do most microorganisms obtain their energy
through a series of orderly and integrated enzymatic reactions leading to biooxidation of carbohydrates
why would an organism use one carbohydrate over another
varying enzyme compliments
what is the function of carbohydrate tests
to determine fermantative pathways
what is the pathway used to describe the fermantation of carbohydrates
glycolytic pathway
one mole of glucose is turned into what
two moles of pyruvic acid
how is fermentative degredation achieved
under anaerobic conditions in a fermentation tube with a durham tube
what is typically found in a fermentation broth
nutrient broth with a specific carbohydrate and a pH indicator
why is there only a specific carbohydrate included in a fermentation broth
determines if the organism can ferment that specific carbohydrate (indicated by the pH indicator)
typically if fermentation has occurred, what colour will the broth turn
will turn yellow which is a negative result
what are positive and negative results based on acidity
positive is if it is basic, negative if it is acidic
what is the longest a broth should go
48 hours is the longest.
when should you let a broth go to 48 hours
if not positive after 18-24 hour window, let it go to a seconf period (up to 48 hours)
how do you get a negative result in carbohydrate fermentation
when the carbohydrate present is not used, the organism will use the peptones in the nutrient broth, using these causes basic conditions (ammonia)
lactose fermentation can distingush between what types of bacteria
enteric and non-enteric
what does TSI stand for
triple sugar iron agar test
what is the function of a TSI test
differentiate between groups of the enterobacteriaceae. tells fermentation patterns and hydrogen sulfide production
what carbohydrate concentration is found in TSI
equal concentrations of lactose, sucrose, and glucose (1%)
what pH indicator is found in TSI
phenol red
how do you innoculate a tsi slant
stab and streak
how is gas production measured in TSI slants
there can be gas bubbles in the media, they can even split the media
how can you tell if only glucose production has occurred in TSI slants
red slant, yellow butt, with or without gas production
how can you tell if lactose or sucrose production has occurred in a TSI slant
yellow slant, yellow butt, with or without gas
how can you tell that no carbohydrate fermentation has occurred in a TSI slant
red slant, red butt
what is the window of time for a TSI slant
18-24 hours strictly
how can you tell if hydrogen sulfide production has occurred in a TSI slant
the mid section will be black (ferrous sulfate reacting with sodium thiosulfate)
what bacteria of medical importance can be found in the enterobacteriaceae
pathogens, occassional pathogens, normal intestinal flora
what comprises the IMViC test
indole, methyl red, voges- proskauer, citrate)
what is tryptophan used for
ability of a bacterium to hydrolyze tryptophan in the presence of indole
what media do you use for indole
SIM
how do you detect the presence of indole in SIM agar
by adding Kovac’s reagent
how do you tell if a positive result for indole in SIM media
after adding kovacs if positive it will turn cherry red
what is the time period for indole (SIM)
24-48 hours
how much kovacs do you add to a SIM tube to detect indole
about 10 drops
what is the major substrate used by all enteric organisms
glucose
when doing the methyl red test, if the solution turns red, what result is this
positive result with a lower pH (more acidic)
how long do you incubate TSB broth
24-48 hours
what is TSB broth used to detect
its the basis for methyl red and voges proskaur tests
what does the voges-proskaur test determine
ability of an organism to produce nonacidic or neutral end products
what is the reagent used in voges proskaur
barritts reagent
how long does it take to perform the voges proskaur test
15 minutes after adding barritts reagent
what colour will the solution be if there is a positive result for voges proskaur
dark red
how do you perform voges proskaur
use innoculated TSB broth, add 10 drops barritts A and shake immediately, then add 10 drops barritts B and shake immediately. leave for 15 minutes, shaking occassionally
what does the citrate test determine
if an organism is able to ferment citrate in the absence of glucose or lactose
what is the pH indicator used in the citrate test
bromthymol blue
what will a citrate positive test show
growth on the surface of the slant and a blue colouration
what will a citrate negative test show
no growth and the media will remain green
what is the incubation time for a citrate test
24-48 hours
how does a SIM tube show hydrogen sulfide production
black
how can you tell motility of an organism
use a SIM tube and when stabbing, if turbidity is outside of the stab line there is motility
what pH indicator is found in urease test
phenol red
what is urease
attacks amide of urea and forms an alkaline end product
how does the urease pH indicator work
urea is split and forms ammonia, this is alkaline and produces a positive red result
what is the incubation time for urease
24-48 hours
what is decarboxylation
some organisms have decarboxylase enzymes capable of removing the carboxyl group of an amino acid.
what is the pH indicator of decarboxylase tests
bromthymol blue
what conditions must be met for LDC and ODC
anaerobic conditions (no oxygen)
how are anaerobic conditions met in ODC and LDC
adding mineral oil to the surface of the innoculated broth
organisms that have deaminase groups can remove what
amino groups from amino acids
is performing a phenylalanine test what happens if the organism has phenylalaine deaminase
phenylpyruvic acid will be released and a green colour will result (positive result)
what reagent is added to phenylalainine tests
10% ferric chloride solution
