Decay of genetic markers for fecal bacterial indicators and pathogens in sand from Lake Superior

Jessica J. Eichmiller, Andrew J. Borchert, Michael J. Sadowsky, Randall E. Hicks

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Beach sands impact water quality and pathogen loads, however, the comparative decay of the fecal indicator bacteria (FIB) Enterococcus spp. and Escherichia coli, and pathogens in freshwater sand have not been examined. In this study, freshwater sand microcosms were inoculated with sewage and pure cultures of bacterial pathogens to compare relative decay rates. The abundance of culturable Enterococcus spp. and E. coli, genetic markers for Enterococcus spp. (Entero1), total Bacteroides (AllBac), and human-specific Bacteroides (HF183), and genetic markers for the pathogens Campylobacter jejuni, methicillin-resistant Staphylococcus aureus (MRSA), Salmonella enterica subsp. enterica serovar Typhimurium, and Shigella flexneri were monitored over the course of two weeks using conventional culture methods and quantitative PCR (qPCR). The effect of moisture on the persistence of culturable FIB and all genetic markers was also determined. In addition, propidium monoazide (PMA) treatment was used to examine differences in the persistence of total genetic markers and those from live cells. Decay rates were statistically compared using Tukey's test. Moisture had a significant (p≤0.05) effect on the decay rates of culturable indicator bacteria, total AllBac markers, and genetic markers for FIB, Salmonella, and MRSA from live cells. At 14% sand moisture, the decay rate of total markers was slower than that of live cells for all qPCR assays, but at 28% moisture, there was no difference in the decay rates of total and live markers for any assay. AllBac and MRSA markers increased in sand at 28% moisture, probably indicating cellular growth. Overall, culturable FIB and HF183 had decay rates that were most comparable to the bacterial pathogen markers examined in this study, whereas Entero1 and AllBac rarely exhibited decay rates similar to the bacterial pathogens in this study. The choice of FIB for assessment of fecal contamination in freshwater sand should take into account the pathogen of concern and sand moisture conditions.

Original languageEnglish (US)
Pages (from-to)99-111
Number of pages13
JournalWater Research
StatePublished - Aug 1 2014

Bibliographical note

Funding Information:
This work was sponsored, in part, by grants from the Minnesota Sea Grant College Program to M.J.S. and R.E.H. (grant number NA07OAR4170009 )., the University of Minnesota Water Resources Center (project number 2011MN291B) to M.J.S. and R.E.H., and the University of Minnesota NIH Biotechnology Training Grant (grant number 2T32GM008347 ). This paper is journal reprint No. 615 of the Minnesota Sea Grant College Program.


  • Decay rate
  • Fecal indicator bacteria
  • Freshwater
  • Pathogenic bacteria
  • Persistence
  • Sand


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