USE OF DELAYED INCUBATION MEMBRANE FILTER TEST FOR DETERMINING COLIFORM BACTERIA IN SEAWATER

The use of the delayed incubation membrane filter test (MF) for the enumeration of coliform bacteria in freshwater has been substantiated. The relative effectiveness of the method for coliform assay in seawater has not been reported in the literature. The known antimicrobial activity of seawater discourages the practice of sample storage prior to bacteriological analysis. The limitations imposed by the lack of adequate field equipment, personnel and relative proximity of the examining laboratory may make immediate analysis impractical or even impossible. Under these circumstances, it was deemed desirable to evaluate the performance of this delayed incubation procedure on seawater samples. A comparison of the delayed incubation (DMF) and immediate incubation (IMF) procedures revealed no significant difference in the recovery of coliform bacteria for the salt water samples analyzed. Although the data suggest lower DMF/IMF ratios at lower pollution stations and higher DMF/IMF ratios at higher pollution stations, there is statistically no significant difference in coliform recovery by the two methods. As a result, the delayed incubation procedure can be expected to provide results far superior to those obtained from samples stored in bottles under various conditions of time and temperature. © 1969.