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Thermo Scentific

Dehydrated Culture Media


Code: CM0079

A medium for the detection of thermophilic anaerobic organisms.

Typical Formula*




Sodium sulphite


Iron (III) citrate




pH 7.1 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards

Suspend 23.0g in 1 litre of distilled water and boil to dissolve completely. Sterilise by autoclaving for 15 minutes at 121°C. Mix well before pouring.

This medium is a modification of Cameron Sulphite Agar developed by the National Canners Association of America 1.

It had been shown that the medium was improved by reducing the concentration of sodium sulphite. Beerens 2 showed that some strains of Clostridium sporogenes would not tolerate 0.1% sulphite. This was confirmed by Mossel et al.3 who consequently used iron sulphite agar containing only 0.05% sulphite and obtained no apparent inhibition.

Iron Sulphite Agar is particularly suitable for the detection of thermophilic anaerobic organisms causing sulphide spoilage in food. The medium should be dispensed in 10ml amounts in tubes for deepshake cultures, and inoculated whilst fluid at about 50°C. Allow to set and incubate at 55°C for thermophilic species. Desulfotomaculum nigrificans, the type species, produces distinct black spherical growths in the depth of the medium.
In the Attenborough and Scarr method 4, diluted samples of the sugar were filtered through membrane filters which were then rolled up and placed in tubes containing enough melted Iron Sulphite Agar (at approximately 50°C) to cover them. The medium was allowed to solidify and the tubes were incubated at 56°C. After 48 hours the number of black colonies on the membrane was counted. This membrane filter technique is quicker than the standard method but of comparable accuracy, and permits the examination of a much larger sample 5.

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 medium below 25°C.

Dehydrated medium: Light straw coloured, free-flowing powder
Prepared medium: Straw-grey coloured gel

Quality Control

Positive controls:Expected results
Clostridium sporogenes ATCC® 19404*Good growth; blackening
Desulfotomaculum nigrificans ATCC® 19858Good growth; blackening
Negative control:  
Escherichia coli ATCC® 25922*Good growth; no blackening
* This organism is available as a Culti-Loop®

The blackening reaction is only presumptive evidence of clostridial growth. Confirmation tests must be carried out to identify the organism growing in the medium.

1. Tanner F. W. (1944) `The Microbiology of Foods’ 2nd ed., Garrard Press, Illinois p. 1127.
2. Beerens H. (1958) DSIR, Proc. 2nd Internat. Symp. Food Microbiol. 1957, HMSO, London, pp. 235-245.
3. Mossel D. A. A., Golstein Brouwers G. W. M. V. and de Bruin A. S. (1959) J. Path. Bact. 78. 290-291.
4. Attenborough Sheila J. and Scarr M. Pamela (1957) J. Appl. Bact. 20. 460-466.
5. Bufton A. W. J. (1959) J. Appl. Bact. 22. 278-280.

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