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Applied and Environmental Microbiology, March 2009, p. 1517-1524, Vol. 75, No. 6
0099-2240/09/$08.00+0     doi:10.1128/AEM.02278-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Growth of Enterococci in Unaltered, Unseeded Beach Sands Subjected to Tidal Wetting{triangledown} ,{dagger}

Kevan M. Yamahara, Sarah P. Walters, and Alexandria B. Boehm*

Department of Civil and Environmental Engineering, Environmental and Water Studies, Stanford University, Stanford, California 94305-4020

Received 3 October 2008/ Accepted 6 January 2009

Enterococci are indicator bacteria used to assess the risk of acquiring enteric disease from swimming in marine waters. Previous work identified beach sands as reservoirs of enterococci which can be transported from the sand to the sea, where they may instigate beach advisories. The present study establishes that naturally occurring enterococci can replicate in beach sands under environmentally relevant conditions. In unseeded, nonsterile microcosm experiments, it was shown that intermittent wetting of sands by seawater, like that which would occur at the high tide line, stimulates the transient replication of enterococci at rates of 0.20 to 0.63 per day (equivalent to doubling times of 1.1 to 3.5 days). Replication was not observed in control microcosms that were not subjected to wetting. Enterococci were enumerated using both culture-dependent (membrane filtration and mEI media) and culture-independent (quantitative PCR [QPCR], 23S rRNA gene based) techniques, which allowed tracking of both culturable and total enterococcus populations. Inhibition of QPCR and DNA extraction efficiencies were accounted for in the interpretation of the QPCR results. The results provide evidence that enterococci may not be an appropriate indicator of enteric disease risk at recreational beaches subject to nonpoint sources of pollution.

* Corresponding author. Mailing address: Department of Civil and Environmental Engineering, Environmental and Water Studies, Stanford University, Stanford, CA 94305-4020. Phone: (650) 724-9128. Fax: (650) 725-3164. E-mail: aboehm{at}stanford.edu

{triangledown} Published ahead of print on 16 January 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, March 2009, p. 1517-1524, Vol. 75, No. 6
0099-2240/09/$08.00+0     doi:10.1128/AEM.02278-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Heaney, C. D., Sams, E., Wing, S., Marshall, S., Brenner, K., Dufour, A. P., Wade, T. J. (2009). Contact With Beach Sand Among Beachgoers and Risk of Illness. Am J Epidemiol 170: 164-172 [Abstract] [Full Text]  


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