question
botulism food poisoning
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caused by Clostridium botulinum. when endospores grow improperly in foods
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salmonella and campylobacter
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cause illness when eggs and poultry products are not cooked well.
question
coliform count
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determines food spoilage and contamination with potential to spread diseases from fecal matter
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Known contaminants of water
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vibrio cholerae
Salmonella typhi
shigella dysenteriae
Salmonella typhi
shigella dysenteriae
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why is it not reasonable to test for known contaminants of water?
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specific pathogens are fastidious and can be overgrown by other bacteria causing them to be missed in analysis
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instead of testing water for pathogens, it is better to test for....
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Indicator bacteria because it could indicate the presence of all fecal contamination
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viruses are more difficult to detect because...
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they cannot be grown in a medium
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A good indicator is
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E-coli
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features of a good indicator
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found in intestines of humans and other mammals
can be identified using specific microbial tests
not as fastidious as other bacteria and can survive longer in water samples
can be identified using specific microbial tests
not as fastidious as other bacteria and can survive longer in water samples
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E-coli and Enterobacter aerogenes are designated as
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coliforms
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coliforms are
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gram negative
facultative anaerobic
non spore forming rods that ferment lactose with acid
facultative anaerobic
non spore forming rods that ferment lactose with acid
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presumptive test
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15 tubes are used to see if the water contains any lactose fermenting bacteria that produces gas
also test for the most probable number of coliforms per 100ml of water.
also test for the most probable number of coliforms per 100ml of water.
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confirmed test
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use media to grow only coliform bacteria by inhibiting the growth of gram-positive bacteria
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EMB agar
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used in confirmed test
coliforms produce large blue-black colonies that have a green sheen for E-coli
coliforms produce large blue-black colonies that have a green sheen for E-coli
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Endo agar
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used in confirmed test
coliforms produce pink to red colonies
coliforms produce pink to red colonies
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completed test
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check if isolate from agar plate in the confirmed test matches the definition of coliforms
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steps in confirmed test
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Durham tube to check if lactose gas in produced
agar slant to check if gram negative bacteria, non-sporing and rod shaped
agar slant to check if gram negative bacteria, non-sporing and rod shaped
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completed test does not differentiate between
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E-coli and Enterobacter aerogenes
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E-coli and Enterobacter aerogenes can be differentiated by
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IMVIC test
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membrane filter method (mfm)
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the most reliable method to determine coliforms in water in the U.S
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membrane filter method uses
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a membrane with a specific pore size which water is poured through and bacteria larger than the pore size is retained and put on a petri dish with absorbent pad saturated with endo broth. plate is indubated at 35 degrees celcius for 24 hrs and individual cells
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in the endo broth of mfm
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acid produced from fermentation interacts with basic fuchsin, a dye in medium causing coliform to have a negative metallic sheen.
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total coliform count in mfm is determined by
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the volume of water filtered
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