Simple method for concentration of bacteria from large volumes of tap water.

Membrane adsorption-elution techniques have made it possible to concentrate and detect small numbers of viruses in large volumes of water and wastewater, but no such methods are available for quantitative recovery of bacteria. A number of waterborne disease outbreaks of "unknown etiology" in the United States are suspected to have been caused by pathogens present in numbers too small to be detected by currently available methodology. The present study reports on the use of positively charged depth filters for the concentration and detection of bacteria in large volumes of tap water. In this method, dechlorinated tap water was passed, under positive pressure, through positively charged filter media (Zetaplus, 05S). More than 90% of seeded bacteria adsorbed to these filters at ambient pH levels. Adsorbed bacteria were eluted by passing a small volume of Trypticase soy broth in the direction opposite of the influent flow. By this method, Escherichia coli and Salmonella serovar B organisms in 20 liters of tap water were concentrated in a final volume of 50 ml, with an average recovery efficiency of greater than or equal to 30%.