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Material Safety Data Sheet

Required Products

Organisms

Organisms this product works with:

For this Organism

Other products used in the isolation of Yeasts:

Dehydrated Culture Media

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DRBC AGAR BASE

Code: CM0727

Dichloran Rose-Bengal Chloramphenicol Agar is a selective medium for yeasts and moulds associated with food spoilage.

Typical Formula*

gm/litre

Peptone

5.0

Glucose

10.0

Potassium dihydrogen phosphate

1.0

Magnesium sulphate

0.5

Dichloran

0.002

Rose-Bengal

0.025

Agar

15.0

pH 5.6 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards

CHLORAMPHENICOL SELECTIVE SUPPLEMENT

Code: SR0078

Vial contents

 SR0078E
(1 vial per 500ml medium)

SR0078H
(1 vial per 2 litres medium)

per litre

Chloramphenicol

50mg

200mg

100mg

 

Directions
Suspend 15.75g in 500ml (31.5g/l) of distilled water and heat to dissolve completely. Reconstitute one vial SR0078E per 500ml medium or one vial SR0078H per 2 litres medium, as directed. Add the vial contents to the DRBC Agar Base. Sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C, mix well and pour into sterile Petri dishes.

Description
Dichloran Rose-Bengal Chloramphenicol Medium (DRBC) is based on the formulation described by King et al.1,2, and is recommended as a selective medium for the isolation and enumeration of yeasts and moulds that are of significance in food spoilage.

DRBC is a modification of Rose-Bengal Chloramphenicol Medium3 and differs as follows: pH is lowered to 5.6, the Rose-Bengal content is reduced by 50% and Dichloran is added.

The cumulative effect of these modifications is to further inhibit bacterial growth, inhibit spreading moulds such as Rhizopus and Mucor and make the medium capable of supporting the growth of those species that cannot be isolated on Rose-Bengal Chloramphenicol Agar or acidified Potato Dextrose Agar1. The inhibition of spreading moulds and the general restriction of colony size results in improved enumeration and detection of mycotoxigenic moulds and other species of significance in food spoilage6.

In a collaborative exercise in the UK between nine laboratories, in which mould and yeast counts were made on different samples of food and feed, DRBC came out best of the five different media tested7.Rose-Bengal Chloramphenicol Agar should be used in addition where it is necessary to gain an overall impression of the fungal flora, including spreading types, when the use of DRBC Agar alone would inhibit these.

The reduced pH of DRBC Agar increases the inhibition of yeasts by Rose-Bengal1 and the use of Rose-Bengal Chloramphenicol Agar (pH of 7.2) in parallel should be considered where it is necessary to enumerate yeasts in the presence of moulds.

Technique

  1. Prepare the DRBC Medium as directed using CM0727 and SR0078.
  2. Add 40ml of the food sample to 200ml of 0.1% peptone water and process in a Seward `Stomacher’ for 30 seconds4 or alternatively weigh into 0.1% peptone water and leave for 30 minutes shaking periodically5.
  3. Inoculate 0.1ml of the prepared sample on the medium surface.
  4. Incubate the plates at 25°C and examine after 3, 4 and 5 days.
  5. Report as number of colonies per gram of food.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared plates of medium at 2-8°C.

Appearance
Dehydrated medium: Pink coloured, free-flowing powder
Prepared medium: Pink coloured gel

Quality control

Positive controls:

Expected results

Aspergillus niger ATCC®9642*White / Yellow mycelium, black spores
Saccharomyces cerevisiae ATCC® 9763*

Good growth; pink coloured colonies

Negative controls:

 
Escherichia coli ATCC® 25922 *No growth

Bacillus subtilis ATCC® 6633*

No growth

* This organism is available as a Culti-Loop®

Precautions
ROSE-BENGAL PHOTO-OXIDISES TO FORM TOXIC COMPOUNDS. STORE PLATES OF THE MEDIUM IN THE DARK AND AVOID EXPOSURE TO LIGHT 8.
Some strains of fungi may be inhibited on this medium.
The dichloran compound used in this medium is Botran® 2,6-Dichloro-4-Nitro-Analine (CAS: 99-30-9).

References
1. King D. A. Jr., Hocking A. D. and Pitt J. I. (1979) J. Appl. & Environ. Microbiol. 37. 959-964.
2. Pitt J. I. (1984) Personal Communication.
3. Jarvis B. (1973) J. Appl. Bact. 36. 723-727.
4. Sharp A. N. and Jackson A. K. (1972) Applied and Environmental Microbiology. 24(2). 175-178.
5. Sharf J. M. (ed) (1966) 2nd ed American Public Health Association, New York.
6. Thomson G. F. (1984) Food Microbiol. 1. 223-227.
7. Seiler D. A. L. (1985) Int. J. Food Techn. 2. 123-131.
8. Kramer C. L and Pady S. M. (1961) Trans. Kan. Acad. Sci. 64. 110-116.

 
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