Mode of Action
The presence of Enterococci, especially E. faecalis, E. faecium, E.durans and E.hirae, serves as an indicator for faecal contamination.
Growth of Enterococci is stimulated by selected peptones, phosphates and addition of Tween® 80. Enterococci cleave the unique chromogenic substrates in the medium. This produces red colonies allowing an easy detection of Enterococci.
Sodium azide and ox bile inhibit most accompanying microbial flora. Non-Enterococci produce colourless, blue/violet or turquoise colonies. These colonies are easily distinguished from the red coloured colonies Enterococci produce.
Typical Composition (g/litre)
Peptones 10.0; sodium chloride 5.0; sodium azide 0.2; dipotassium hydrogenphosphate 3.4; potassium di-hydrogenphosphate 1.6; ox bile 0.5; Tween® 80 1.0; chromogenic-mixture 0.25; agar-agar 11.0
Suspend 33.0 g in 1 litre of demin. water by heating in a boiling water bath or in a flowing steam. Stir the contents to assist dissolution (approx. 45 minutes), let the medium cool to 45-50 °C and pour into plates.
n Do not autoclave! Do not overheat!
pH. 7.0 ± 0.2 at 25 °C
The plates are clear and slightly yellow. If stored at +4 ± 2 °C and protected from light the plates are stable for 2 weeks.
Inoculate the medium by the pour-plate-method or by spreading the sample material on the surface of the plates. In addition the membrane-filter-technique can also be used.
The type of membrane filter affects the performance of the medium (growth and colouration of colonies). Best results were obtained using membrane filters of cellulose-mixed-ester material, e.g. Gelman GN-6 (OSSMER, 1999).
Incubation: 24 ± 4hours at 35-37 °C.
If this will neither result in a colour change nor in visible growth continue the incubation up to 44 ± 4 hours.