Biochemical Tests Flashcards
What is the oxidase test?
Tests for ability to oxidize TMPD in Gram (-) bacteria, rapid reaction is if cytochrome C is present to accept e-
TMPD (red) + cyt c (ox) –> TMPD (ox - purple) + cyt c (red)
(+) : purple colour in 5 seconds
What is the catalase test?
Tests Gram (-) and (+) for catalase enzyme that prevents cell death by H2O2
2 H2O2 –> 2 H2O + O2
(+) : bubbles
What is the ONPG test?
Tests Gram (-) for ability to hydrolyze LACTOSE
uses ONPG (ortho-nitrophenyl-galactopyranoside) as substrate for Beta-galactosidase
ONPG –> O-nitrophenol (yellow) + galactose
(+) : yellow
What is the DMCA test?
Tests Gram (-) for action of TRYPTOPHANASE - intracellular enzyme
Cells metabolize tryptophan in medium –> indole and serine
DMCA lyses cell, releases indole
indole + DMCA = blue-green spot
(+) : blue-green spot within 20 sec
What is the Urease Test?
Tests Gram (-) for urease intracellular enzyme to hydrolyze urea
urea + H2O –> 2 NH3 + CO2
ammonia increases pH, phenol red –> pink/cerise colour
(+) : cerise colour
What is EMB media?
Selective for Gram (-)
Differential for lactose fermentation.
(+) : Mixed acid fermentation –> green/metallic sheen
(+) : Butandiol fermentation –> fish eye
(-) : Non-fermenters –> colourless, or tinted from agar
What is Azide Dextrose Broth?
Selective Enrichment Broth for Streptococci Aerotolerant Anaerobes
Has Respiratory poison azide that blocks electron transport along cytochrome.
What is TCS + 7.5% NaCl Broth?
Selective Enrichment broth for staphylococcus species.
High [salt] –> inhibits most bacteria via dehydration and plasmolysis.
Staph. species are salt tolerant, accumulate K+ to increase cytoplasmic [solute]
What is Lactose Broth?
Presumptive Test for E. coli.
Fermentation pathways of lactose react with phenol red to give a yellow colour + gases trapped inside Durham vial.
Organisms that do not use lactose can grow on other components of media – other rxns possible
What is KF agar?
Selective, Presumptive Test for Fecal Streptococci including E. faecalis.
Azide and bromocresol purple inhibit other bacteria.
Fermentation of maltose and lactose –> acid that reacts with bromocrescol purple & reduction of tetrazolium dye = yellow agar + red colonies.
What is the test for Growth at 45 degrees?
In BHI
E. faecalis will grow at elevated temperatures in rich media
Can also survive for 30 min at 60 degrees.
Mesophilic, non sporeforming will die
What is the coagulase test?
Tests for virulence factor of S. aureus.
Coagulase is an extracellular protein that is an exotoxin released by S. aureus. Enables clotting of fimbrin.
Cells are mixed with citrated plasma, that is a chelator of cations, preventing normal clotting reaction. (Requires cations).
