Competition of Escherichia coli O157 with a drinking water bacterial community at low nutrient concentrations

In contrast to studies on (long-term) survival of enteric pathogens in the environment, investigations on the principles of their growth and competition with autochthonous aquatic bacteria are rare and unexplored. Hence, improved basic knowledge is crucial for an adequate risk assessment and for understanding (and avoiding) the spreading of waterborne diseases. Therefore, the pathogen Escherichia coli O157 was grown in competition with a drinking water bacterial community on natural assimilable organic carbon (AOC) originating from diluted wastewater, in both batch and continuous culture. Growth was monitored by flow cytometry enabling enumeration of total cell concentration as well as specific E. coli O157 detection using fluorescently-labelled antibodies. An enhanced competitive fitness of E. coli O157 with higher AOC concentrations, higher temperatures and increased dilution rates (continuous culture) was observed. A classical "opportunist" versus "gleaner" relationship, where E. coli O157 is the "opportunist", specialised for growth at high nutrient concentrations (μ(max): 0.87 h(-1) and K(s): 489 μg consumed DOC L(-1)), and the bacterial community is the "gleaner" adapted to nutrient-poor environments (μ(max): 0.33 h(-1) and K(s): 7.4 μg consumed DOC L(-1)) was found. The obtained competition results can be explained by the growth properties of the two competitors determined in pure cultures and it was possible to model many of the observed dynamics based on Monod kinetics. The study provides new insights into the principles governing competition of an enteric pathogen with autochthonous aquatic bacteria.