Seasonal variation in survival of Escherichia coli exposed in situ in membrane diffusion chambers containing filtered and nonfiltered estuarine water.

Human fecal Escherichia coli isolates were exposed over a seasonal cycle to estuarine water in diffusion chambers filled with double-filtered (0.45 and 0.2 microns) and nonfiltered water. Laboratory manipulations of E. coli cultures before estuarine exposure were reduced to minimize sublethal stress, and nonselective or resuscitative enumeration techniques were employed to maximize recovery of stressed cells. E. coli was capable of extended survival during in situ exposure to estuarine water, provided eucaryotes were excluded from diffusion chambers. Survival was directly related to temperature in absence of the eucaryote component of the natural microbiota. Although it was not possible to prevent eventual bacterial contamination in double-filtered water, there was no direct evidence that such contamination affected E. coli survival. Conversely, E. coli disappearance was most pronounced at warmer temperatures in the presence of the natural microbiota, and decline coincided with increasing eucaryote densities. In contrast, the decline of E. coli during winter was similar in both filtered and nonfiltered seawater.