Water: use the membrane filtration technique. Add the membrane on medium surface and incubate at 36°C ± 2°C for 48 hours. After
incubation all red, maroon or pink colonies as presumptive enterococci. Presumptive colonies are confirmed by transferring the
membrane on a Bile-Esculin Agar plate and incubating at 44°C ± 0.5°C for 2 hours. Black-brown colonies are confirmed.
Food: samples are homogenised and diluted with physiological saline. Homogenates or dilutions are spread evenly over the agar
surface with a glass rod and allowed to soak in. Plates are incubated at 35°C for 48 hours, after which typical colonies are counted.
Besides the water and food applications, the medium may be used by direct plating for other purposes.
RESULTS & INTERPRETATION
Enterococci produce red or maroon colonies. All red, maroon or pink colonies as presumptive enterococci. Not all species reduce the
triphenyltetrazolium chloride therefore pale colonies should not be ignored.
Enterococcus faecalis ATCC 29212: good growth; deep red coloured colonies.
Escherichia coli ATCC 25922: no growth.
1. ISO 7899-2:2000: Water quality -- Detection and enumeration of intestinal enterococci -- Part 2: Membrane filtration method.
2. Slanetz and Bartley Agar. Biokar diagnostics - product leaflet.
3. CM0377 Slanetz and Bartley Medium (Enterococcus Agar). Oxoid - product leaflet.
Tryptose 20.0 g, yeast extract 5.0 g, glucose 2.0 g, Di-potassium hydrogen phosphate
4.0 g, sodium azide 0.4 g, 2,3,5-triphenyltetrazolium chloride 0.1 g, agar 10.0 g.
Distilled water ad 1000 ml, pH 7.2 ± 0.2.
Bring to the boil to dissolve the agar completely. Do not autoclave! Dispense into Petri
The reduction of triphenyltetrazolium chloride to an insoluble formazan is seen by the
formation of red to maroon colonies. Sodium azide inhibits the growth of
The medium is used for the enumeration of enterococci in foods and water by membrane filtration technique, but also can be used as
a direct plating medium.
(c) Costin Stoica