Modification of the interaction betweenEscherichia coli and bacteriophage in saline sediment

The effects of sorption phenomena on the interaction between a parasite and its host bacterium have been investigated using anEscherichia coli-bacteriophage-saline sediment system. The sediment contained organic matter and a high proportion of clay, predominantly montmorillonoid. BothE. coli and phage remained firmly sorbed to saline sediments or montmorillonite, but were rapidly desorbed following dilution of the electrolyte below a critical concentration. This desorption coincided with the dispersal of sediment colloids.Escherichia coli was protected from phage attack by the presence of sediment, montmorillonite, or organic matter at salinty levels both above and below this critical point for dispersal and desorption. Evidence is presented indicating thatE. coli is protected from phage attack at low electrolyte concentrations by an envelope of sorbed colloidal materials around the cell, whereas at high electrolyte concentrations protection results both from the colloid envelope around the cells as well as from the sorption of cells and phages to solid particles. The protection ofE. coli and possibly other fecal bacteria may result in their accumulation in saline sediments, producing a possible health hazard in estuaries and lagoons if the bacteria are desorbed following dilution as a result of heavy rainfall.