Relative Abundances of <i>Enterococcus faecalis</i> , <i>Enterococcus faecium</i> , and <i>Enterococcus casseliflavus</i> across Wastewater Treatment Unit Processes

High Resolution Image Download MS PowerPoint Slide Three Enterococcus species (i.e., casseliflavus, faecalis, and faecium ) were previously found to have dissimilar decay kinetics during disinfection. It is therefore possible for the relative abundances of viable bacteria of each species to shift as the bacterial population is subjected to treatment processes, which may subsequently impact the disinfection of the enterococci population as a whole. Therefore, this study was conducted to assess the relative abundances of different enterococci species in wastewater as it flows through treatment processes. Culture-based, qPCR, and hybrid culture-qPCR methods were used to assess the distribution of E. faecalis, E. faecium and E. casseliflavus in samples of wastewater influent, primary effluent, secondary effluent, and postchlorination final effluent; grab samples were collected quarterly over a year from one facility. Using qPCR, E. faecium concentrations ranged between 1.1- and 2.6-log greater than E. faecalis and E. casseliflavus . The species distribution of culturable isolates did not change between influent and secondary effluent; however, it was significantly different postchlorination, with E. faecium being the only culturable species identified. While this study assessed just one treatment facility, consistent results over a year illustrate that culture-based methods do not provide a full picture of enterococci disinfection and persistence, given the varying relative abundances of viable Enterococcus species.