Differential tests continued

1
Differential tests continued

• 5-7 5-11 5-12 5-15

2
From last week

• Phenol red broth (sucrose and dextrose) ex 5-2
• PH indictor phenol red turns yellow below a pH of
  6.8
• Durham tube inverted inside will catch CO2 gas if
  produced
• Check tubes for color (acid produced if yellow)
  and presence of gas bubble (CO2)

3
MRVP-ex. 5-3

• MR test is Methyl red-designed to detect
  organisms capable of mixed acid fermention
• Add methyl red to ½ the contents of the tube (5
  drops)
• If it stays red it is positive for mixed acid
  fermentation (positive MR)
• Orange is NOT red (inconclusive) and yellow is
  negative
• The VP is Voges-Proskauer and is for organisms
  that ferment glucose and turn the acid into
  acetoin and 2,3 butanediol.
• VP reagents are added and if the mixture is red,
  it is positive. (15 drops VP a and 10 drops VP b
  and MIX well)

4
Nitrate reduction ex. 5-6

• Nitrate broth tests for the presence of nitrate
  reductase
• Some can perform denitrification and convert
  Nitrate to molecular nitrogen (gas) will have
  bubble if a durham tube is present
• Add nitrate reagent A and nitrate reagent B to
  the test tube-red color means the bacteria
  reduced nitrate to nitrate.
• To verify the results, add zinc to negative test
  tubes.
• RED after zinc verifies the negative (it reacts
  with the zinc).

5
New Stuff

• Citrate- ex. 5-7
• Starch hydrolysis-ex. 5-11
• Urea hydrolysis-ex. 5-12
• DNA hydrolysis test-did not get the media so omit
  this one. 5-15.
• Inoculate tubes in the usual way, inoculate the
  plate (starch) in the usual way.