Labs for midterm 2 Flashcards
What kind of agar is MacConkey agar
Selective(due to the presence of bile salts) and differential culture (differentiates between organisms that produce acid from lactose and those that do not)
Gram negative (enterobacteriaceae), because it inhibits the growth of gram positive bacteria
Lactose fermenters turn pink
The slow growing organisms have to be supplied with ___
A richer medium to increase their growth rate or even to allow them to grow
What is the difference between selective and differential media
Selective- inhibiting growth of some organisms while allowing others to grow
Differential- appearing different in the presence of certain organisms
What kind of agar is Mannitol salt agar
Has a high sodium chloride levels and a mannitol, and a ph indicator
Only Halotolerant and halophiles can grow
Mannitol fermenters turn the medium yellow
This media is selective (due to the salt content) and differential ( between organisms that produce acid from mannitol and those that do not)
What is the purpose of Milk agar
If there is a clear zone around colony=production of caseinase
What is the purpose of Starch agar
To see of the starch is broken down IODINE should be added first.
Clear zone around colony=production of amylase
In general why do we use Milk, Starch agar, peptone iron, etc.
To demonstrate the biochemical characteristics of an organism with differential media
How does phenol red-sugar-Durham tube work
The media contain either glucose, lactose , or sucrose, and a pH indicator in the form of phenol red + Durham red to capture the gas
The media turn yellow if acid is produced ( the organism used the sugar as source of energy) + gas can be produced or not
How does peptone iron agar work
It has cysteine that some organisms can degrade to yield H2S by the enzyme cysteine desulfurase
Positive reaction for production of H2S and degradation of cysteine-> black precipitant
Explain the reactions in nitrate broth and the experiment
The broth has Nitrate salt only. Some organisms can reduce nitrate to nitrite.
Others can reduce nitrite further to yiled N2 that is volatile
If the tube turned red-> nitrate reducer
No red -> added Zn-> red-> no reduction of nitrate
No red -> added Zn-> no red-> denitrifiers ( reduced nitrate to N2)
What does IMViC stand for and how it is used
Used to differentiate members of Gram negative intestinal bacili
I-indole(tryptophan)
Methyl red
Voges-Proskauer
Citrate
What does each test in IMViC detect
Indole test: the production of indole form tryptophan Tryptophan broth+Kovac’s reagent: red ring= indole reducer
Methyl red: indication of the extent of acid production from the glucose in MR-VP medium. MR+methyl red, pinl=acid production from glucose
VP(voges-proskauer): determine if the organisms produce acetyl methyl carbinol. VPI and VPII is added to MR-VP. Pink=production of acetyl methyl carbinol
Simmons Citrate Agar: bright blue->organism use citrate as its sole acetyl methyl carbon source
Physical methods of bacterial control and how do they work
- Moist heat: coagulation of proteins
- Dry heat: oxidation of cell components
- UV light : dimerization of thymine(DNA damage).
What is photoreactivation
Exposure of culture to visible light after UV light-> start to live again
Wavelength 365-450 nm
Spores are ____ to physical methods
More resistant
