Microbiology lab 4 (lab 4 selective and differential media)
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mannitol salt agar
- - isolates staphylococcus bacteria
- from other types of bacteria.
- This is how bacillus megaterium
- looks like in the MSA:
- This is how Staphylococcus aureus looks
- like in the MSA:
Selective feature: high amount of salts
Differential: mannitol and phenol red
vogel johnson agar
- between pathogenic strains of staph. Aureus.
- Differential: Mannitol and potassium tellurite
- (pathogenic strains of staph. Aureus have the enzyme coagulase which acts on
- potassium tellurite, which produces metal tellurite which gives a black
- -If the plate produces yellow and black deposits,
- then the strain of staph aureus is pathogenic.
- Bile alts and crystal violet dye
- Differential: lactose and neutral
- red (which turns pink in acidic conditions)
- Coliforms (non-pathogenic intestinal
- and stomach bacteria) and pathogenic
- enteric bacteria (are capable of living in the intestine and they are pathogenic)
- -Coliforms can only
- ferment lactose.
eosin methylene blue agar (EMB)
- Selective: eosin Y (which inhibits growth of gram +
- bacteria) and methylene blue
Differential: lactose and sucrose
- If bacterium produces slightly acidic conditions in
- this plate, that part of the plate will turn purple (ex. Salmonella)
- If bacterium produces very acidic conditions, that
- part of the plate will turn metallic green (ex. E Coli)
brilliant green agar
-differentiates salmonella from fecal specimen
- Specific: Brilliant green dye (inhibits all gram +
- and most gram -)
Differential: lactose and phenol red and sucrose
- -phenol red àin the absence of acid is
- red, in acidic conditions is yellow
-E Coli produce yellow color
-Salmonella produce pink color
- growth of pathogenic enteric bacteria.
- - differentiates b/t shigella and salmonella
- (both of which are pathogenic)
- Selective: bile salts (inhibits gram
- Diff. 1: lactose and bromothymol
-E Coli à yellow
- Diff. 2: another differential feature is à ferric ammonium citrate and
- sodium thiosulfate (react with H2S (which is produces by pathogenic
- enterobacteria) to produce a black deposit
- -supports growth of only pathogenic
-contains 5-10% sheep blood
-RBC à contains heme and globin
- a. β hemolysis- indicates a very pathogenic
- bacterium. This bacterium consumes both globin and heme. Produces a clear zone
- of inhibition around it
- b. α hemolysis- bacteria only consumes heme protein,
- not globin. Greenish color. Moderately pathogenic.
- c. γ (gamma) hemolysis- least
- pathogenic. Silverish tinge.
When using selective and differential media, why is it important to use TSA as well?
as a positive control
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