Microbiology Lab Final Exam Test Questions – Flashcards
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Which organisms can ferment lactose?
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E. coli E. cloacae E. aerogenes K. pneumonia
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Define caliform bacteria
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rod-shaped, Gram-negative, non-spore forming, and motile or non-motile bacteria which can ferment lactose with the production of acid and gas
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Name the selective medias used in class
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Blood Agar Bile Esculin Mannitol Salt Agar (MSA) MacConkey Agar (MaC) Eosin Methylene Blue (EMB) Hektoen Enteric Agar (HEA) Xylose Lysine Desoxiolate (XLD)
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Name the differential medias used in class
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O/F Glucose MRVP Catalase Oxidase Citrate Starch Indole TSI
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What does the acronym IMViC stand for?
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indole methyl red vogues proskaver in citrate
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What is the IMViC series of tests used for?
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used to differentiate gram negative rods
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Which specific orgnaisms are the IMViC tests good at differentiating?
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Enterobacter
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Define selective media
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designed to grow only specific bacteria but not others
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Define differential media
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designed to show the difference between different organisms grown on
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What does blood agar show?
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shows the types of hemolysis (ability to break down RBCs) of organisms
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What are the 3 types of hemolysis?
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alpha beta gamma
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Describe alpha growth on blood agar
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partial growth, green
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Describe beta growth on blood agar
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total growth, clear
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Describe gamma growth on blood agar
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nothing, still red
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Bile esculin shows what?
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ability of organisms to tolerate bile and hydrolyze esculin
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What two types of organisms is bile esculin good at differentiating?
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enterococci and streptococci
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What reagant is added to bile esculin?
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ferric citrate
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What could be the results of a bile esculin test?
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black is +
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What two types of organisms usually grow on bile esculin?
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enterococci streptococci
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MSA stands for
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Mannitol Salt Agar
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MSA shows what?
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If the organisms produces acid products
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MSA is used to identify which organism?
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S. aureus
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What is the indicator in MSA whether the fermentation takes place or not?
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phenol red
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What is the result of a positive MSA test?
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yellow is +
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MaC stands for
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MacConkey Agar
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MaC shows what?
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If the organism is a lactose fermenter
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What are the possible outcomes of a MaC test?
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good growth indicates a gram negative bacterium that is not inhibited by crystal violet or bile. pink to red growth without bile indicates that the organism produces acid from lactose fermentation and is a probable coliform. colorless growth is a non lactose fermenting organism and noncoliform.
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Can gram positive organisms grow on MaC?
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No
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EMB stands for
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Eosin Methylene Blue
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EMB shows what?
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tests if an organism is caliform
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What are the possible results of an EMB test?
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dark growth indicates a lactose fermenter and acid production pink growth indicates lactose fermenter
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HEA stands for
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Hektoen Enteric Agar
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HEA shows what?
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indicates lactose fermentation and hydrogen sulfide production
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HEA is used for?
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isolates salmonella & shigella bacteria
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What are the possible results of a HEA test?
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pink growth indicates lactose fermenter and sulfur reducer
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XLD stands for
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xylose lysine desoxiolate
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XLD shows what?
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if an organism can ferment the sugar xylose to produce acid
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XLD is used for?
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isolates salmonella & shigella bacteria
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What are the possible results of XLD test?
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yellow indicates acid production red with some black growth indicates sulfur reduction
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O/F in O/F glucose stands for
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oxidative/fermentation
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O/F glucose tests show what?
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does the organism oxidize and/or ferment glucose
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What could be the results of an O/F glucose test?
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2 tubes, one with oil (anaerobic) and one not: yellow in anaerobic means fermenting glucose but if yellow only in aerobic, then oxidizing glucose
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MRVP stands for what?
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methyl red vouges proskaur
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MRVP shows what?
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MR- tests for acid fermentation VP- can it ferment glucose
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What could the results of the methyl red look like?
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red is + yellow is -
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What could the results of vouges proskauer look like?
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red is + nothing is -
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Catalase tests for what?
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does the organism have catalase
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What could be the results of a catalase test?
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bubbles indicates catalase is present no bubles is -
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Define catalase enzyme
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catalyzes the decomposition of hydrogen peroxide to water and oxygen (H₂O² → H₂O + O₂)
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Oxidase tests for what?
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does the organism have cytochrom c oxidase
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What could be the results of oxidase test?
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if the organism becomes blue after 20 secs then cytochrome c oxidase is present
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Define oxidase enzyme
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an enzyme that promotes the transfer of a hydrogen atom from a particular substrate to an oxygen molecule, forming water or hydrogen peroxide.
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Citrate tests for what?
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can the organism use citrate as its sole source of carbon
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What could the results of a citrate test be?
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any amount of blue is + growth but no blue means citrate is utilized nothing is -
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Starch tests for what?
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can the organism break down starch
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What would a positive starch hydrolysis test look like?
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plate appeared white and cloudy where hydrolysis occurred, black is original color
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Indole tests for what?
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does the organism have tryptophan
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What will a positive indole test look like?
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red ring
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What reagant is added to an indole test?
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kovac's reagant
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TSI stands for
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triple sugar iron
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TSI test for what?
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used to differentiate bacteria on the basis of glucose fermentation, lactose fermentation, sucrose, and sulfur reduction
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What could be the results of a TSI test?
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cracks indicate gas production black precipitate indicates sulfur production red slant with yellow butt indicates glucose fermentation yellow slant indicates glucose and lactose fermentation
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Define restriction digest
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aids in the protection of foreign DNA, restriction enzymes function by binding to the DNA and cutting out damaged portions. sites are short, usually 4-8 nucleotides
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What is the charge of DNA?
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negative
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What determines how far a molecule will move in gel electrophoresis?
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its molecular weight
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Describe the role ethydium bromide gel electrophoresis
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binds to DNA and will fluoresce under a UV light
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Define restriction enzymes
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an enzyme produced chiefly by certain bacteria, having the property of cleaving DNA molecules at or near a specific sequence of bases (restriction sites)
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Define plasmid
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a genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium
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Which test tests for acetoin?
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Vouges Proskauer
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Give an example of a motile bacteria
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E. coli can be
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