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SCHAEDLER ANAEROBE AGAR

Code: CM0437

A medium free from thioglycollate for the growth of aerobic and anaerobic organisms.

Directions
Suspend 40g in 1 litre of distilled water and boil to dissolve the medium completely. Sterilise by autoclaving at 121°C for 15 minutes. Mix well before pouring.

Description
Schaedler, Dubos and Costello¹ formulated this medium for the isolation of aerobic and anaerobic micro-organisms from the gastro-intestinal tract of mice. Mata, Carrillo and Villatoro² modified the formula in their studies on anaerobic human faecal microflora. The modified formula has been used in Oxoid Schaedler Anaerobe Agar/Broth and the medium can be used to create selective conditions under which the required, delicate and more nutritionally exacting micro-organisms of the intestinal tract would develop, despite the presence of antagonistic organisms. Normally such fastidious micro-organisms would be swamped by the growth of enterococci, coliform bacilli and other Gram-negative bacilli.

In both studies^1,2 the use of the base medium with selective agents (shown overleaf) for the isolation and enumeration of Lactobacillus, Streptococcus, Clostridium, Bacteroides and Flavobacterium species from faecal samples and various organs of the digestive tract.
Although thioglycollate is widely used in anaerobic media, to lower the redox potential in order to favour growth of anaerobic organisms, some workers have reported it to be inhibitory to some anaerobes^3,4.

Schaedler Anaerobe Agar contains cysteine hydrochloride and glucose, as reducing substances, with the advantage that cysteine inhibits the growth of Escherichia coli. Kari, Nagy, Kovacs & Hernadi⁵ have reported the inhibitory effect of cysteine on several enzymatic reactions of Escherichia coli in vitro.

Schaedler Anaerobe Agar has been shown to be a suitable alternative to blood agar for the enumeration of clostridia⁶ and has been used for the examination of food, waste products and ditch water⁷. These authors showed the necessity for strict anaerobic conditions for the successful recovery of obligate anaerobes when using this medium without the addition of blood.

Investigations at Oxoid have shown that Schaedler Anaerobe Agar gave similar results in recovery and colonial appearance to Oxoid Blood Agar Base No.2 when tested with the same organisms.

Technique
The sample suspension is diluted as necessary in order to obtain separated and countable colonies. A calibrated loopful is then spread on the surface of a previously dried Schaedler Anaerobe Agar plate. Conditions of incubation will vary according to the type of culture under test. Pure cultures may grow on the base medium and this is also used for general aerobic and anaerobic counts.

In the enumeration of Enterococcus faecalis (facultatively anaerobic) as an indicator organism in dehydrated or frozen foods and water, and for the detection of Clostridium, the medium can be used as follows:

Food sample (e.g. pre-cooked frozen food) suspensions are plated out by the surface spread technique and an aerobic viable count may be carried out at 25°C and 35°C. For pre-cooked meat products, an anaerobic viable count and a selective plate examination for Clostridium perfringens should also be performed.

Addition of Selective Agents
To 1,000ml of base agar, the following selective agents may be added:
1. Medium for anaerobic lactobacilli and anaerobic streptococci: NaCl 10.0g; Neomycin 0.002g. Incubate anaerobically at 35°C.
2. Medium for Bacteroides and clostridia: Placenta powder 2.0g; Neomycin 0.002g. Incubate anaerobically at 35°C.
3. Medium for flavobacteria: 7ml of 0.5% tyrothricin in ethanol. Incubate aerobically at 35°C.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Prepared plates may be stored at 2-8°C if suitably protected.

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

Quality control

* This organism is available as a Culti-Loop®

Precautions
Note the comment on strict anaerobic conditions for obligate anaerobe isolation without blood.

References
1. Schaedler R. W., Dubos R. and Castello R. (1965) J. Exp. Med. 122. 59-66.
2. Mata L. J., Carrillo C. and Villatoro E. (1969) Appl. Microbiol. 17. 596-599.
3. Hibbert H. R. and Spencer R. (1970) J. Hyg. Camb. 68. 131-135.
4. Mossel D. A. A., Beerens H., Tahon-Castel Baron G. and Potspeel B. (1965) Ann. Inst. Pasteur de Lille 16. 147-156.
5. Kari C., Nagy Z., Kovacs P. and Hernadi F. (1971) J. Gen. Micro. 68. 349-356.
6. de Waart J. and Pouw H. (1970) Zbl. I. Abt. 0rig. 214. 551-552.
7. de Waart J. (1973) Personal Communication.