Micro - Biochemical Testing II Flashcards
Are biochemical tests to determine the genotype or phenotype of an organism?
Phenotype
Two types of general biochemical tests as they relate to speed of the test
Rapid test
- spot tests = immediate reaction
- same-day tests = 4 hours or less
Conventional tests
-single tube tests usually within 18-24 hrs
Single enzyme tests (6)
Catalase
Coagulase
Oxidase
Indole
Urease
PYR
Catalase converts ___ into…
Hydrogen peroxide
Water and oxygen
This group of organisms do not have catalase
Obligate anaerobes
-lethal for them
Catalase differentiates these 3 major genera of organisms: Staph, Strep, Listeria. What are the test results for each?
Staphylococcus and Listeria = positive
Streptococcus = negative
Weak bubbling or bubbling that takes place a few minutes later is catalase ___
Negative
-positive must be IMMEDIATE bubbling
When should we perform a coagulase test?
For gram-positive cocci that are catalase positive
-need to determine if organism is Staph aureus
What organism (genus/species) does the slide coagulase test SCREEN for? What test do we use to CONFIRM if it’s this organism?
Staph aureus
-most virulent Staph
Tube coagulase test
- read every 30 mins for 4 hrs
- incubate and read after 18 hrs if negative
Which coagulase test is used to detect bound coagulase and which is used to detect free coagulase?
Slide coagulase test = bound coagulase
Tube coagulase test = free coagulase
Both slide and tube coagulase tests are based on this mechanism that causes coagulation
Bound coagulase on cell wall or free coagulase converts fibrinogen to insoluble fibrin clot
When doing the tube coagulase test, why should we check on the tube every half hour for up to 4 hours to determine if there’s coagulation?
Staphycoccus produces staphylokinase, which dissolves the fibrin clot
-causes false negative results
Oxidase is an enzyme that is involved in what types of reactions?
Redox reactions
- catalyzes transport of electrons from donor compounds (NADH) to electron acceptors
- Kovac’s reagent acts as artificial electron acceptor and changes color
The oxidase test is used to differentiate gram-positive or gram-negative bacteria? Differentiates what groups of organisms? Enterobacteriaceae are catalase positive or negative?
Gram-negative
Non-enterics from enterics
Negative
An organism that is oxidase positive will convert the reagent, ___, into this color… A negative result looks like this…
Kovac’s
Blue-purple
No color change
Positive and negative QC cells for catalase test are
Positive control = Staph aureus
Negative control = Strep pyogenes
Positive and negative QC cells for oxidase test are
Positive control = Pseudomonas aeruginosa
Negative control = E coli
The indole test detects the presence of the enzyme ___, which hydrolyzes the amino acid ___ into ___
Tryptophanase
Tryptophan
Indole
The indole test is used in the differentiation of this group of organisms. The test is useful for the identification of these two organisms in the group that test positive…
Anaerobes/Enterobacteriaceiae
E. coli
Proteus vulgaris
Bromcresol purple has this color at acidic pH and this color at alkaline pH
Yellow
Purple
Bromcresol blue has this color at acidic pH and this color at alkaline pH
Yellow
Blue
Phenol red has this color at acidic pH and this color at alkaline pH
Yellow
Red/pink