The degree to which a water sample can potentially support the growth of human pathogens was evaluated.
For this purpose, a pathogen growth potential (PGP) bioassay was developed based on the principles of
conventional assimilable organic carbon (AOC) determination, but using pure cultures of selected pathogenic
bacteria (Escherichia coli O157, Vibrio cholerae, or Pseudomonas aeruginosa) as the inoculum. We evaluated 19
water samples collected after different treatment steps from two drinking water production plants and a
wastewater treatment plant and from ozone-treated river water. Each pathogen was batch grown to stationary
phase in sterile water samples, and the concentration of cells produced was measured using flow cytometry. In
addition, the fraction of AOC consumed by each pathogen was estimated. Pathogen growth did not correlate
with dissolved organic carbon (DOC) concentration and correlated only weakly with the concentration of AOC.
Furthermore, the three pathogens never grew to the same final concentration in any water sample, and the
relative ratio of the cultures to each other was unique in each sample. These results suggest that the extent of
pathogen growth is affected not only by the concentration but also by the composition of AOC. Through this
bioassay, PGP can be included as a parameter in water treatment system design, control, and operation.
Additionally, a multilevel concept that integrates the results from the bioassay into the bigger framework of
pathogen growth in water is discussed. The proposed approach provides a first step for including pathogen
growth into microbial risk assessment.