Dichloran Rose Bengal Chloramphenicol (DRBC) Agar

DRBC Agar (Dichloran Rose Bengal Chloramphenicol)

EMD Cat. No. 1.00466.0500

500 g

Selective agar for the enumeration of food spoiling yeasts and molds.

Mode of Action	Preparation
Experimental Procedure and Evaluation	Quality Control
Typical Composition (g/liter)	Interpretation
Literature

Mode of Action
DRBC was developed by KING et al. (1979) and is a modification of Rose-Bengal-Chloramphenicol Agar (RBC from JARVIS (1973). In comparison to RBC, the medium contains Dichloran (0.002 g/l), th pH is lowered to 5.6 and the Rose-Bengal concentration is cut in half (0.025 g/l). This results in an increased inhibition of bacteria and yeasts.
The inclusion of dichloran serves to inhibit the rapid spreading of mucoraceous fungi and restricts colony sizes of other genera, easing the colony count.

Typical Composition (g/liter)
Peptone 5.0; glucose 10.0; potassium dihydrogen phosphate 1.0; dichloran 0.002; magnesium sulfate 0.5; Rose Bengal 0.025; chloramphenicol 0.1; agar-agar 15.0.
pH: 5.6 ± 0.2 at 25 °C.

Preparation
Suspend 31.6 g in 1 liter of purified water and heat to boiling until completely dissolved. Autoclave the medium at 121°C for 15 min. Cool to approx. 50 deg;C, mix well and pour plates.

The appearance of the prepared medium is clear and pink. When stored at +2 to +8°C in the dark, the shelf life of plates is approximately 1 week and in bottles approx. 2 months.

Experimental Procedure
Directly inoculate agar plates using surface spreading technique with serial dilutions.
Incubate at 25 °C and look for growth after 3, 4 and 5 days.

Interpretation of Results
Count the number of colonies per gram of food.
Attention:
Some fungi may be inhibited on this medium. Therefore it is recommended to use Rose Bengal Chloramphenicol Agar (EMD Cat. No. 1.00467.) additionally to examine and identify the complete fungal flora.

Quality control

Test strains	Growth
Saccharomyces cereviseae ATCC 9763	good / very good
Rhodotorula mucilaginosa DSM 70403	good / very good, colony color: orange
Mucor racemosus ATCC 42647	fair / good
Bacillus subtilus ATCC 6633	none
Escherichia coli ATCC 25922	none

Literature

KING, D.A., HOCKING, A.D., and PITT, J.I. (1979) Dichloran-rose bengal medium for enumeration and isolation of molds from foods. Appl. Environm. Microbiol. 37, 959-964.
JARVIS, B. 1973 Comparison of an improved rose-bengal-chlortetracycline agar with other media for the selective isolation and enumeration of molds and yeasts in food. J. Appl. Bacteriol. 36, 723-727.