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72 Cards in this Set
- Front
- Back
What is the definition of carbohydrate fermentation?
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The metabolic process by which an organic molecule acts as an electron donor and one or more of its organic products act as the final electron acceptor
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Carbohydrate fermentation tests are especially useful for differentiating what major group of bacteria?
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Gram-Negative bacilli, especially Enterobacteriaceae
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What role does the phenol red play in phenol red broth?
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pH indicator
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What is the purpose of the Durham tube in the phenol red broth?
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Trap gas that may be produced during fermentation
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Why is reading a phenol red broth test after 18 hours of incubation not recommended?
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B/c of the possibility of a reversion ( A reversion is what happens to the medium when an organism switches metabolic modes from fermentation to deamination after the exhaustion of carbohydrate. It’s impossible to visually distinguish b/t a reversion and a true non-fermenter
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What is reversion?
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A reversion is what happens to the medium when an organism switches metabolic modes from fermentation to deamination of peptone amino acids, AFTER the exhaustion of carbohydrate.
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A yellow color in phenol red broth indicates what medium component has been fermented?
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Carbohydrate
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A yellow color in phenol red broth indicates what medium pH?
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<6.8
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A pink color in phenol red broth indicates what medium component has been catabolized?
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peptone amino acids are deaminated
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A pink color in phenol red broth indicates what medium pH?
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>7.4
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SIM medium is defined broadly as what type of medium?
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Combination Medium
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What are the 3 test performed by SIM medium?
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sulfur Reduction Test
Indole Production Test Motility Tes |
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What does a black precipitate in the butt of a SIM tube indicate?
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indication of Sulfur reduction and a positive test.
Hydrogen Sulfide + Ferric Sulfate Ferric Sulfide (black) H2S (reduced S) + FeSO4 FeS |
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What does growth only along the inoculum path of a SIM tube indicate?
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Negative motility test. Little to no motility
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Negative motility test. Little to no motility
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Positive Motility test. High Motility
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What does a pink color in Kovac’s reagent added to a SIM tube indicate?
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A positive indole reaction and the presence of Tryptophanase
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In terms of oxygen environments, what type of environment does H2S production indicate?
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Anaerobic
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What is the Snyder test used for?
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The Synder test is designed to measure dental caries(tooth decay) susceptibility
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What two groups of oral bacteria does the Snyder medium select for?
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Lactobacilli & oral Streptococci
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What does a positive Snyder test look like?
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yellow in 24hrs.-highly susceptibility
Yellow in 48hrs.-moderate susceptibility Yellow in 72 hrs-Slight susceptibility Green or Yellow in >72hrs. Negative |
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What is the selective property of the Snyder medium?
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Selective for bacteria that can survive low pH (~4,8); favors growth of oral bacteria and discourages growth of others
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What is the bacitracin test used for?
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differentiates beta-hemolytic strep pyrogenes from other beta hemolytic strep
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In the bacitracin test, inhibition of bacterial growth will appear as what?
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inhibition of growth will appear as a clearing of the agar plate
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What is the cell target of bacitracin?
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Cell wall inhibition
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In the bacitracin test, a zone of clearing 10 mm or greater indicates what?
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zone greater than 16mm means bacitracin susceptibility
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What is the novobiacin test most frequently used for?
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most frequently used in presumptively identify the novobiacin resistant stap. saprophyticus
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In the bacitracin test, inhibition of bacterial growth will appear as what?
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a clearing
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In the bacitracin test, a zone of clearing 10 mm or greater indicates what?
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Susceptibility
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Why is Staphylococcus saprophyticus significant?
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it is a common urinary tract pathogen seen in sexually active females
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What is the coagulase test used for in the lab?
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used to differentiate staph. aureus from other gram positive
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What advantage does coagulase production provide to a bacterium?
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coagulase shields the bacteria from phagocytosis by forming the fibrin barriers
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What are the two forms of coagulase?
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bound & free coagulase
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What type of coagulase test did we perform in lab?
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tube test
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What was the fluid used in the coagulase test?
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rabbit plasma treated with anticoagulant
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for bound and free coagulase, what is an advantage of this test?
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the tube test can determine bound or free coagulase whereas the slide can only determine bound
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What was a positive result for the coagulase test performed in the lab?
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positive result=clotting
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What chemical reaction does catalase carry out?
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catalase converts hydrogen peroxide into water and gaseous oxygen
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What indicates a positive reaction in a catalase test?
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positive=bubble formation
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In terms of oxygen-defined groups, what groups of bacteria produce catalase?
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Staphylococcus
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Why must hydrogen peroxide be converted to water and oxygen in the cell?
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hydrogen peroxide is toxic
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What two medically significant genera does the catalase test help differentiate?
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micrococcaceae & streptococcaceae
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What is the selective agent in mannitol salts agar (MSA)?
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sodium chloride
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What genus does MSA select for?
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staphylococci (staph. aureus)
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What is the pH indicator in MSA?
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phenol red
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What does a yellow color change around a colony signify?
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pathogenic staphylococcus
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What is the β-lactamase test used for?
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Rapid test for detecting the presence of B-lactamase(an enzyme that can destroy penicillin-class antibiotics)-- (indicating penicillin & cephalosporins resistant microbes)
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For what bacteria is the β-lactamase test especially useful?
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Especially useful in identifying resistant strains of
Neisseria gonorrhoeae, Staphylococccus spp., and members of genus Enterococcus |
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What is the molecular mode of action of β-lactam antimicrobials?
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The B-lactam ring in the chemical structure of the antimicrobial kills bacteria by interfering with cell wall synthesis
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What is the molecular mode of action of β-lactamase?
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Enzyme produced by bacteria which hydrolyze the B-lactam ring, thus destroying the structure of the antibiotic
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β-lactamase disks are impregnated with what antimicrobial?
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Nitrocefin (a cephalosporin)
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What does a positive β-lactamase test look like?
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it will hyrdolse the nitrocefin Produces pink spot on the disk
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What component of the assay is attached to the latex beads?
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Antigen or antibody
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What is the marker for detecting the antigen-antibody reaction?
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visable aggregate
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What is a positive test in the latex agglutination test?
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clumps of RBC
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What is a negative test in the latex agglutination test?
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nothing happens
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What are latex agglutination tests used for in the clinical laboratory?
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to differentiate the difference between staph and bacterial meningitis
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1.What do bile salts do to Streptococcus pneumoniae cells?
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strep cells are lysed by bile salts
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2. What was the commercial name of the compound used in the disks used to identify S. pneumoniae?
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a. optochin (aka P-disks)
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3. What type of hemolysis does S. pneumoniae produce?
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a. alpha hemolysis
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4. What is the Gram reaction of S. pneumoniae?
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a. gram positive
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1. What is the purpose of the semi-quantitative urine culture?
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a. determining the concentration of the bacteria in urine sample
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2. What type of loop is used for a urine culture?
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a. calibrated loop
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3. What two sizes of loops are available for performing urine cultures?
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a. 0.001mL & 0.01mL
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4. Why do you streak at a 90o angle to the original streak line?
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a. this evenly disperses bacteria over plate
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5. Why would your order this test for one of your patients? (This answer is not in the book).
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a. if patients have the risk for the show symptoms of a urinary tract infection
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5. Why would your order this test for one of your patients? (This answer is not in the book).
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a. if patients have the risk for the show symptoms of a urinary tract infection
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In the antimicrobial agar disk diffusion test, what are the two reasons for incubating the plate once the test has been set up?
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To allow growth of bacteria and time for the agent to diffuse into the agar
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Why are all the aspects of the antimicrobial agar disk diffusion test standardized?
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So that the values read from the chart provide an accurate interpretation of susceptibility or resistance
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In the antimicrobial agar disk diffusion test, what will you observe if the tested organism is susceptible to an antimicrobial?
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A clear zone of inhibition
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What does the acronym “MIC” stand for?
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Minimum Inhibitory Concentration
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What type of dilutions was used to prepare the antimicrobial broth dilution test?
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Broth Dilution Method or Two-fold dilutions
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What is the purpose of the antimicrobial broth dilution test?
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To determine MIC (minimum Inhibitory Concentration) of antimicrobial agent to inhibit bacterial growth
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