Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2009
Publication Date: 5/19/2009
Citation: Jenkins, M., Fisher, D.S., Endale, D.M. 2009. Quicker die-off of fecal indicator bacteria than E. coli 0157:H7 in a pond impacted by animal agriculture [abstract]. American Society for Microbiology Annual Meeting, May 17-21, 2009, Philadelphia, Pennsylvania. Interpretive Summary:
Technical Abstract: Background The USEPA uses concentrations of fecal indicator bacteria, Escherichia coli and fecal enterococci, in surface waters to indicate the potential presence of pathogens such as E. coli O157:H7. The connection between concentrations of indicator bacteria and actual bacterial pathogens in surface waters is based on the assumption that indicators and the pathogens behave similarly. Methods We tested whether death rates under natural conditions of a pond in an agricultural watershed were similar for indicator bacteria and E. coli O157:H7. Known numbers of E. coli, Enterococcus faecium, Enterococcus gallinarum, and E. coli O157:H7 were inoculated into (i) raw pond water and (ii) filtered pond water (to eliminate protozoan predators), and 10-ml aliquots of each inoculated waters were pipetted into sentinel chambers with 0.45µm-pore-size membranes secured at both ends of the chamber to contain the pathogens and indicator bacteria, and allow equilibration with the exterior aquatic environment. Chambers were secured to a floating frame, and placed in the pond at a depth of 50 cm (the extinction depth of UV irradiation). Triplicate chambers were recovered at days 0, 1, 3, 7, 14, 25, and 33, and assayed with IDEXX Colilert and Enterolert reagents for indicator bacteria. E. coli O157:H7 was assayed with a combined MPN enrichment format and TaqMan assay specific for the virulence gene eaeA. Results Fecal enterococci died-off 6-times quicker and E. coli died-off 2-times quicker than E. coli O157:H7. Days to reach 99% die-off for fecal enterococci, E. coil, and E. coli 0157:H7 were 3.7, 9.1, and 19.8 days, respectively. Conclusions These results demonstrated differential rates of inactivation between indicator bacteria and E. coli O157:H7, and underscores the need to develop methods for detecting and enumerating the pathogens themselves.