Survival Potential of Escherichia coli and Enterococci in Subtropical Beach Sand: Implications for Water Quality Managers

Abstract

Fecal bacteria have traditionally been used as indicator organisms to monitor the quality of recreational waters. Recent work has questioned the robustness of traditional indicators, particularly at seawater bathing beaches. For example, a study of Florida beaches found unexpectedly high abundances of Escherichia coli, fecal coliforms, and enterococci in beach sand. The aim of the present study was to explain these abundances by assessing the survival of E. coli and enterococci in beach sand relative to seawater. We used a combination of quantitative laboratory mesocosm experiments and field observations. Results suggested that E. coli and enterococci exhibited increased survivability and growth in sand relative to seawater. Because fecal bacteria are capable of replicating in sand, at least under controlled laboratory conditions, the results suggest that sand may be an important reservoir of metabolically active fecal organisms. Experiments with "natural" mesocosms (i.e., unsterilized sand or water rich in micropredators and native bacteria) failed to show the same increases in fecal indicators as was found in sterile sand. It is postulated that this was due to predation and competition with indigenous bacteria in these "natural" systems. Nonetheless, high populations of indicators were maintained and recovered from sand over the duration of the experiment as opposed to the die-off noted in water. Indicator bacteria may wash out of sand into shoreline waters during weather and tidal events, thereby decreasing the effectiveness of these indicators as predictors of health risk and complicating the interpretations for water quality managers.

Routine screening of harmful microorganisms in beach sands: Implications to public health

“…S. aureus possesses a wide tolerance for environmental stresses such as high salinity and variations in osmotic pressure. High levels of S. aureus and P. aeruginosa, previously reported at three South Florida beaches (Esiobu et al, 2004), may be explained by the ability of these organisms to replicate in sand over a range of conditions, and the sand may also offer an environment favorable to pathogen growth through biofilm development (Hartz et al, 2008). Biofilms provide protection against extreme changes in moisture, salinity, and other environmental variables as well as provide some protection against predators, as reviewed in Fanning and Mitchell (2012).…”

“…Several authors have reported that both indicator bacteria and potential pathogens occur in beach sands of both freshwater and marine environments (Sanchez et al, 1986;Ghinsberg et al, 1994Ghinsberg et al, , 1995Obiri-Danso and Jones, 2000;Desmarais et al, 2002;Sato et al, 2005;Vantarakis et al, 2005;Beversdorf et al, 2007;Bonilla et al, 2007;Vogel et al, 2007;Hartz et al, 2008;Abdelzaher et al, 2010). In fact, bacterial cell numbers can be substantially higher in the sand than in nearby waters; for example in the Great Lakes region of the US, E. coli in sand can be found at levels of 10 to 100 times higher than adjacent waters, generally ranging from 10 3 to 10 4 CFU/g at an enclosed beach to 10 1.5 to 10 2.5 CFU/g at open beaches (Burton et al, 1987;Doyle et al, 1992;Irvine and Pettibone, 1993;Oshiro and Fujioka, 1995;Whitman and Nevers, 2003;Yamahara et al, 2007).…”

“…The origins of these microorganisms in sand are often unclear, but they are likely from both exogenous (e.g., sewage or run-off) and/or indigenous sources (e.g., regrowth within the sediments) (Ferguson et al, 2005) and from humans and animals present on the beach ). The presence, persistence, and accumulation of FIB in sediments show that beach sands are likely reservoirs for these microbes and thus can have an impact on water quality (Byappanahalli et al, 2003;Boehm and Weisberg, 2005;Beversdorf et al, 2007;Yamahara et al, 2007;Hartz et al, 2008;Halliday and Gast, 2011).…”

Dietary habits of urban pigeons (Columba livia) and implications of excreta pH – a review

“…Any uric acid remaining in voided excreta will be continually degraded by aerobic and anaerobic bacteria if exposed to moisture (Lindeboom 1984), but may crystallise to less soluble forms under dry conditions. Faecal bacteria may survive even the harshest of conditions (Hartz et al 2008) and continue to degrade the faecal matter outside the body. Finally, faecal matter is considered to be an excellent substrate for fungi, bacteria, lichen and mosses (García-Rowe & Saiz-Jimenez 1991), not to mention the invertebrate activity, which can also continue physical and chemical changes once the excreta are voided.…”

Population dynamics and genetic variability of Escherichia coli in a mixed land-use watershed

“…E. coli and fecal coliform concentrations often are higher in sediments or beach sand than in overlying water columns (Crabill et al 1999;Bonilla et al 2007). This has been attributed to better survival (Enzinger & Cooper 1976;An et al 2002) and/or regrowth (Hartz et al 2008) of fecal indicator bacteria owing to the presence of organics, a decreased level of UV radiation, and the presence of anaerobic regions in sediments/beach sand.…”