[Esculin hydrolysis, a confirmation test for fecal streptococci detected on Slanetz-Bartley medium]

Samples of marine waters have been analyzed for recovering faecal streptococci applying the membrane filtration technique on Slanatez-Bartley medium. It has been pointed out that this medium can yield high proportions of non-group D streptococci: in fact its selectivity seems to be rather low at least for certain samples. This study aims to test and to overcome the disadvantage of the high counts of faecal streptococci due to background microrganisms. The hydrolysis of esculin may be used as a confirmatory test for increasing the selectivity. Membranes showing high numbers of streptococci-like colonies have been transferred from Slanetz-Bartley (MEA) medium to an esculin iron agar (EIA) plate. After 20 min at 41 degrees C small black spots appeared on the backside of the membrane where the colonies had hydrolyzed esculin were resident. The number of positive colonies may be recorded as the real number of faecal streptococci.