Slanetz and Bartley Medium

Detect and enumerate enterococci from water and food samples with Thermo Scientific™ Slanetz and Bartley Medium. Slanetz and Bartley¹ originally devised this medium to detect and enumerate enterococci by the technique of membrane filtration, but it has also proved useful as a direct plating medium^2,3. The medium is very selective for enterococci, and when it is incubated at elevated temperatures (44-45°C), all red or maroon colonies may be accepted as presumptive enterococci^4,5. The medium has been tested in accordance with the methods described in ISO 7704:2023.

The Environment Agency Microbiology of Drinking Water 2002⁶ recommends the use of Slanetz and Bartley medium for the enumeration of enterococci in water supplies, as does ISO in the standard for water quality⁷.

The water is filtered through a membrane filter which is then placed on the surface of a well dried plate of the medium. Plates are incubated at 36 ±2°C for 44 ±4 hours and then at 44 ±0.5°C for 2 hours. Membranes are examined, with a hand lens in a good light, and all red or maroon colonies counted as enterococci.

Food samples can be examined for enterococci by the method suggested by the Nordic Committee of Food Analysis³. Samples are homogenized and so diluted with physiological saline that only 15 to 150 colonies grow on each Petri dish. Homogenates or dilutions are spread evenly over the agar surface with a glass rod and allowed to soak in. Dishes are inverted and incubated at 35°C for 48 hours, after which typical colonies (pink or dark red, with a narrow whitish border) are counted.

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