lab exam #2 Flashcards
what are the types of biochem tests done on enterobacteriacea?
- phenol red broth
- triple sugar iron agar
- MR-VP broth
- urease
- SIM media
- citrate
- EMB media
what test is done to differentiate between staphylococci and streptococci?
catalase test
result: only staphylococci will be positive for the enzyme catalase.
(S. aureus, S. Saprophyticus, S. epidermis)
What tests are done to differentiate between ONLY staphylococci?
- coagulase test
- DNase
- mannital salt agar (MSA)
What tests are done to differentiate between ONLY streptococci?
- blood agar plate - hemolysis
- bile esculin
what is the phenol broth test?
differential test.
it checks for the fermentation of glucose and lactose (PRG and PRL)
a positive result would be a yellow broth, meaning it is acidic and ferments lactose/glucose!
a negative result would be fuschia.
has a durham tube to check for gas production.
what is the triple sugar iron agar test?
differential media.
use both loop and needle!
a red/orange slant that tests for the fermentation of glucose, sucrose, and lactose!
what are some results for the TSA test?
if orange: not inoculated properly.
K/K = all pink. no fermentation
A/A = all yellow. fermentation of all 3!
K/A = fermentation for ONLY glucose.
if black precipitate is seen, it is positive for H2s production (hydrogen sulfide gas)
if lifting is seen on A/A slant agar, C02 gas was produced.
what is the MR-VP broth test?
differential media.
MR stands for methyl red.
PR stands for Voges-Proskauer.
tests for the production of neutral OR acidic waste products from glucose fermentation.
The MR test is acidic!
The VP test in neutral!
Has to be one or the other. CANNOT be positive for both.
What is the urease test?
differential media.
a beige colored slant!
tests the production of the enzyme urease which converts urea into ammonia and C02
pink slant = positive for the enzyme urease!
yellow slant = negative!
what is SIM media?
differential media.
a deep! use needle.
sulfur, indole, and motility + H2S production.
- tests for the breakdown of the amino acid tryptophan into indole from the reduction of sulfur!
reagent used for this test is Kovac’s reagent.
yellow band = negative for the amino acid breakdown
pink band = positive.
what is the citrate test?
differential.
green colored slant!
- tests for the use of citrate as a sole carbon and energy source.
green slant = negative for the use of citrate
blue slant = positive for the use of citrate as its sole carbon source.
What is EMB media?
eosin methylene blue - burgundy colored plate.
is DIFFERENTIAL: allows certain microbes (lactose fermentors) to be visually distinguished by the appearance of the colony or the surrounding media.
is SELECTIVE: inhibits the growth of gm+, only gm- grows!
any type of growth = gm-
pink growth = weak lactose fermentor
metalic green growth = rapid lactose fermentor (E. coli !! )
What is the catalase test?
differential media.
it determines if the microbe produces the enzyme catalase and is used to differentiate between staph and strep!
the enzyme catalase breaks down hydrogen peroxide into water and gaseous oxygen.
this test has you add a drop of hydrogen peroxide then add an inoculated colony to see if bubbles form, which indicates if catalase is present.
only STAPHYLOCOCCI will produce bubbles.
what is the coagulase test?
differential media.
it is used to differentiate amongst STAPHYLOCOCCI organisms using rabbit plasma!
Coagulase is only used by S. aureus to cause the formation of blood plasma clots, a means of defense for the bacteria.
SOLID = (+) S. aureus
liquid = (-)
what is the DNase test?
differential media.
an agar plate containing bound DNA.
helps to distinguish S. aureus from other staphylococci.
S. aureus produces the exoenzyme DNase, which breaks down DNA from the host cell.
If DNase is excreted onto the media, it hydrolyzes DNA into smaller pieces and the methyl green becomes unbound, leaving a clearing around the bacterial growth.
