Influence of Enterococcal Surface Protein (esp) on the Transport of Enterococcus faecium within Saturated Quartz Sands

Abstract

Enterococcus was selected by US EPA as a Gram-positive indicator microorganism for groundwater fecal contamination. It was recently reported that enterococcal surface protein (esp) was more prevalent in Enterococcus from human sources than in Enterococcus from nonhuman sources and esp could potentially be used as a source tracking tool for fecal contamination (Scott et al., 2005). In this research, we performed laboratory column transport experiments to investigate the transport of Enterococcus faecium within saturated quartz sands. Particularly, we used a wild type strain (E1162) and a mutant (E1162Δesp) to examine the influence of esp on the transport behavior of E. faecium. Our results showed that esp could significantly enhance the attachment of E. faecium cells onto the surface of silica sands and thus lower the mobility of E. faecium within sand packs. Cell surface properties (e.g., zeta potential) were determined and the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to explain the effects of esp on the retention of E. faecium. Overall, our results suggested that E. faecium strains with esp could display lower mobility within saturated sand packs than E. faecium strains without esp. The disparity in the transport behavior of E. faecium with and without esp could limit the effectiveness of esp as a source tracking tool within the groundwater system.

Comparison of the transport of Bacteroides fragilis and Escherichia coli within saturated sand packs

“…Hydrodynamic dispersion of colloid-sized particles (such as the bacterial cells) has been previously shown to be negligible for uniform sands such as were used in this experiment [17,18]. To facilitate the comparison of the mobility of E. coli and B. fragilis within the saturated sand packs, the clean-bed deposition rate coefficients (k d ), which measure the rates at which bacterial cells were being removed from the aqueous phase under pristine conditions (i.e., the sand surfaces are free of bacterial cells), were estimated from the early cell breakthrough concentrations in the effluent [24][25][26]:…”

“…The B. fragilis cells were then harvested through centrifugation (4000 g, 10 min, 4 • C). The fresh bacterial pellets were rinsed 4 times using the appropriate electrolyte solution to remove the growth media [17,18].…”

“…The AB force ˚A B can be attractive or repulsive, as it is caused by hydrophobic or hydrophilic interactions between the bacterium and the sand. For the cell-sand system (sphere-plate geometry), the forces can be calculated using the following equations [17,[30][31][32][33]:…”

“…The use of Bacteroides spp. for groundwater MST, however, can be complicated by their mobility within the aquifer matrix [17]. If the mobility of Bacteroides spp.…”

Enterococci in the Environment

“…A quantitative PCR (qPCR) method for esp fm has been developed and used in field studies in Australia (4). Interestingly, the presence of the esp gene was found to affect the transport of E. faecium in saturated quartz sands by lowering bacterial mobility through increased attachment to sand particles (184).…”