Determination of Coliforms in Foods Using Violet Red Bile Agar

6. MATERIALS AND SPECIAL EQUIPMENT

The following media (1, 3 to 8) are commercially available and are to be prepared and sterilized according to the manufacturer's instructions. See also (8.1) and Appendix G of Volume 2.

1) Peptone (0.1%) Water diluent (PW)

2) 2% aqueous sodium citrate (tempered to 45 ⁰ C) (for cheese samples only)

3) Nutrient Agar (NA)

4) Tryptic Soy Agar (TSA)

5) Levine's Eosin Methylene Blue (L-EMB) agar or Endo agar

6) Brilliant Green Lactose 2% Bile (BGLB) broth

7) Lauryl Sulfate Tryptose (LST) broth

8) Violet Red Bile (VRBA) Agar

9) Double Strength Violet Red Bile Agar

10) Stomacher, blender or equivalent

11) pH meter or paper capable of distinguishing to 0.3 to 0.5 pH units within a range of 5.0 to 8.0.

12) 1N HCl and 1N NaOH

13) Gram stain reagents

14) Light microscope

15) Positive and negative control cultures, ATCC or equivalent (see Table II)

16) Incubator capable of maintaining 35 ° C

Note: It is the responsibility of each laboratory to ensure that the temperature of the incubators or waterbaths are maintained at the recommended temperatures. Where 35 ° C is recommended in text of the method the incubator may be 35 +/-1.0°C. Similarly, lower temperatures of 30 or 25 may be +/- 1.0 ° C. However, where higher temperatures are recommended, such as 43 or 45.5 ° C, it is imperative that the incubators or water baths be maintained within 0.5 ° C due to the potential lethality of higher temperatures on the microorganism being isolated.

17) Colony counting device (optional)

18) Control strains; use the suggestions listed in Table II, using ATCC or equivalent strains.

7. PROCEDURE

Each sample unit may be analyzed individually or the analytical units may be combined. Carry out the test in accordance with the following instructions:

7.1 Handling of Samples Units