A Membrane Filtration Technique for the Enumeration of Escherichia coli in Seawater

S ummary . Membrane filtration has become an accepted method for enumerating Escherichia coli in water, but little published evidence could be found to judge the specificity of the method to assess faecal contamination in either fresh or saline waters. The method is used in our laboratory to monitor the extent and degree of sewage pollution in coastal areas, but there is need for information on what proportion of lactose-fermenting colonies from seawater, developing at 44° on a 4% enriched Teepol medium, are E. coli type I. A total of 1352 colonies from seawater was tested for production of indole and for gas from lactose at 44°. In addition, 46% of the colonies were screened by the IMVEC series of tests. The proportion of colonies tested ranged from 10–100%, depending on the number of colonies on the membrane. Many of the colonies (81.9%) to which IMVEC tests were applied were E. coli type I; a further 10.9% were Irregular type I. The practical implications of these findings are discussed.