Lab Exam 3: Selective And Differential Media Flashcards
What is the main resource for identifying the genus and species of a bacteria
Bergey’s Mannual of Systematic bacteriology
What growth mediums favor the growth of gram-negative organisms and allow distinctions to be made between types of Graham negative bacteria based on the ability to ferment sugars in the media
EMB and MAC
Both selective and differential
What type of medium is mannitol salt auger MSA
Selective and differential. Favors the growth of organisms that can tolerate the 7.5% salt concentration and the ability to ferment mannitol
Medium selected for gram-positive bacteria and inhibits most Graham negative bacteria. Should be compared to a control plate
PEA
Contains 7.5% sodium chloride and the sugar mannitol and phenol red
Both selective and differential
Yellow =
MSA
Yellow= fermented mannitol
Select for Graham negative
Differential for lactose fermentation
PH indicator-turns pink/red when low pH (ferments lactose)
MAC
Selective and differential
Inhibits gram-positive bacteria and differentiate based on ability to ferment lactose and or sucrose
Use for isolation of fecal coliform‘s
EMB
Metallic green sheen or dark purple growth indicates lactose fermenter
Growth = gram -
Differentiate space on the organisms ability to ferment or oxidize carbohydrates
One out of the two tubes inoculated will be covered with mineral oil to promote anaerobic growth in fermentation
What do the results mean?
Oxidation-fermentation glucose
If both the sealed and unsealed tubes are yellow the organism ferments and oxidizes
If the organism oxidizes only, the medium in the unsealed two will turn yellow while the sealed one will stay green
If the seal tube is green in the unsealed tube is green with blue on top the organism is non-saccharoyltic
Broth that contain a single carbohydrate either glucose fructose sucrose lactose or mannitol
And a pH indicator Phenol red
PR broth
Yellow and or gas = fermentor
Bright pink= positive for peptization
- this test identifies mix acid from any bacteria it determines if an organism exhibits formic hydrogenase activity
- identifies bacteria capable of fermentation and production of acetone instead of organic acids
MR-VP broth
MR- red on top is positive, yellow is negative
PV- red is positive and yellow is negative
Purpleish color on slide indicates positive result
Add 1 to 3 drops of oxidase
Oxidase reaction
Gas production and/or red color are positive results
If no color change add zinc.
If it turns red it is negative and yellow is positive
Nitrate reduction
-used pH Indicator bromthymol blue
Positive if it turns royal blue
Positive if there is growth but no color change
Simmons citrate agar
Citrate as only carbon source
Selective in differential media use on ability to hydrolyzed esculin. Bile inhibits gram-positive organisms except D streptococci enterococi
Bile Esculin Agar (BEA)
If more than half of the tube is dark brown it is positive
Test for the presence of amylase.
Start hydrolysis test
If a halo is seen around the bacteria it is positive
Used to determine if an organism exhibits urease activity
The enzyme urease converts urea to ammonia and carbon dioxide which will increase the pH of the media
Urea hydrolysis
Pink is positive
Orange is negative
The presence of a pink halo around the growth indicating the organism hydrolyzed the DNA into small fragments in nucleotides (toluidine blue)
If (methyl green) is used a positive result is a clear halo
DNA hydrolysis
A differential medium that test for the reduction of sulfur, indole production and motility
SIM medium
Blackening of the media is positive for H2S production
Red is positive for indole
Tests to determine H2S production
SIM, KIA, or TSI
Used to determine anaerobic and aerobic bacteria
Has a phenol red pH indicator
KIA
- Slant and butt red = non-fermenter
- slant is hot pink (P+), butt is yellow =(glucose fermentor but not sucrose or lactose)
- all yellow = ferments lactose and or sucrose, glucose
- Black butt = H2S +
Beta hemolysins-
Alpha hemolysins-
Gamma hemolysins-
Beta- completely lyce the red blood cells and a transparent halo around the growth of bacteria
Alpha- only partially degrades, appearance of green to brown pigmented around the bacterial growth
Gamma- growth on the bacteria without any observable change, no hemolysins produce
Test use for differentiating gram positive
Clotting indicates a positive result
Coagulase test
Test to determine if the bacteria is flagellated
Motility deep
What is a positive result for phenylalanine deaminase test?
Dark green color. No color change is negative
Removes amene groups from amino acids
Zone > 10 is sensitive
Differentiates beta Group A from resistant B step
Bacitracin
Zone > 16 =sensitive
Differentiates coagulase - bacteria
Novobiocin
Zone > 14
Differentiates S. Pneumonia
Optochin