PRESENCE-ABSENCE (P-A) BROTH

Technical Data #5061a / 2005.08.31

Presence-Absence Broth (P-A Broth) is used for the detection of coliforms in treated water. One large test portion (100 ml) based on the principle that no coliforms should be present in 100 ml of drinking water, replaces the multiple-tube procedure for the presence or absence of lactose fermentors. Bromcresol purple is the indicator dye. Lactose fermenting bacteria turn the medium from purple to yellow with or without gas.

 

FORMULA
in grams per liter purified filtered water

 

Casein Peptone

9,83
Gelatine Peptone

5,0
Beef Extract

3,0
Lactose

7,46
Potassium Phosphate, dibasic

1,35
Potassium Phosphate, monobasic

1,35
Sodium Chloride

2,46
Sodium Lauryl Sulfate

0,05
Bromcresol Purple

0,0085

pH 6,8 +/- 0,2 at 25º C

This approximate formula may be adjusted and/or enriched to obtain best results.


PRECAUTIONS
This medium is for laboratory use only.


STORAGE
Store prepared media at 2-8º C protected from direct light and dehydrated powder, in a dry place in tightly-sealed containers at 2-25º C.


SIGN OF DETERIORATION
Media should not be used if the expiry date has passed. Prepared media should not be used if there are signs of contamination (evaporation or discoloration). Do not use dehydrated media if it is caked.


DIRECTIONS
For a triple strenght concentration, suspend 91,5 g in 1000 ml of purified water. Heat gently with frequent agitation to dissolve completely. Dispense 50 ml into 250 ml screw-cap milk dilution bottle. Sterilize at 121º C for 15 minutes.


PROCEDURE
Bring prepared medium at room temperature before inoculation.

  1. Inoculate with 100 ml of water sample and invert bottle several times.
  2. Incubate at 35° C for 24-48 hours.
  3. Positive acid reaction turns the purple broth to yellow color.
  4. Shake bottle gently and observe for gas production (foaming reaction).


QUALITY CONTROL
Expected results after 24 hrs at 35ºC

 

Organisms

ATCC

Growth

Color

Gas
Escherichia coli

25922

+

yellow

+/-
Escherichia coli

11775

+

yellow

+/-
Pseudomonas aeruginosa

27853

-

-

-

LIMITATIONS OF METHOD
Bacteria isolated after 48 hours incubation may not be considered as positive presumptive test for coliforms. This is only a part of the identification. Others tests may be required.


REFERENCES

  1. Atlas, R.M., 1997 Hanbook of Microbiological Media 2nd, ed. L.C. Parks editor CRC Press
  2. Standard Methods for Examination of Water and Wastewater 1989 17th ed. APHA Washington D.C.


CATALOGUE NUMBERS 

Dehydrated media 500 g QB-39-3522
     
Prepared media    
Bottle 250 ml, 50 ml 10/pkg 5061