Dichloran Glycerol (DG18) Agar

DG18 Agar (Dichloran Glycerol Agar)

EMD Cat. No. 1.00465.0100/0500

100 g, 500 g

Selective agar with low water activity (aw) for the enumeration and isolation of xerophilic molds in dried and semi-dried foods as well as a general purpose medium for counting yeast and molds in foodstuffs.

Dichloran glycerol (DG 18) agar was formulated by HOCKING and PITT (1980) and is recommended for the enumeration of xerophilic molds in dried and semi-dried foods, such as dried fruits, meat and fish products, spices, confectionery, cereals, nuts. BECKERS et al. (1982) demonstrated the use of DG 18 as a general purpose medium for counting yeasts and molds in foodstuffs.

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

Mode of Action
By reducing the water activity from approx. 0.99 to 0.95 with 18 % (w/w) glycerol and addition of chloramphenicol growth of bacteria is prevented. 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; chloramphenicol 0.1; agar-agar 15.0.
pH:5.6 ± 0.2 at 25°C.
The prepared plates are clear and yellowish.

Preparation
Suspend 31.6 g in 1 liter of purified water and heat to boiling until completely dissolved. Add 175 ml of glycerol p.a. (EMD Cat. No. 1.04092.) to the medium, mix and autoclave at 121°C for 15 min. Cool to approx. 50°C, mix well and pour plates.
The appearance of the prepared medium is amber and slightly opalescent. 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.

Interpretation of Results
Count the number of xerophilic colonies per gram of food.

Experimental Procedure
Directly inoculate agar plates using surface spreading technique with serial dilutions.
Incubate at 22-25°C and look for growth after 4, 5 and 6 days.
Interpretation of Results
Count the number of xerophilic colonies per gram of food.

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

HOCKING, A.D., and PITT, J.I. (1980) Dichloran-glycerol medium for enumeration of xerophilic fungi from low moisture foods. Appl. Environm. Microbiol. 39, 488-492.
BECKERS, H.J., BOER, E., VAN EIKELENBOOM, E., HARTOG, B.J., KUIK, D., MOL, N., NOOITGEDACHT, A.J., NORTHOLD, M.O., and SAMSON, R.A. (1982) Inter. Stand. Org. Document ISO/TC34/SC9/N151.