| Water Health 04 (2006) 313-320
Seasonal persistence and population
characteristics of Escherichia coli and enterococci in deep backshore sand
of two freshwater beaches
Muruleedhara N. Byappanahalli, Richard
L. Whitman, Meredith B. Nevers, W. T.Evert Ting and Charles C. Tseng
United States Geological Survey, Great Lakes
Science Center, Lake Michigan Ecological Research Station, 1100 North Mineral
Springs Road, Porter,Indiana, 46304,USA, Tel: +1 (219) 926-8336, Fax: +1
(219) 929-5792, rwhitman@usgs.gov
United States Geological Survey, Great Lakes
Science Center, Lake Michigan Ecological Research Station, 1100 North Mineral
Springs Road, Porter,Indiana, 46304,USA, Tel: +1 (219) 926-8336, Fax: +1
(219) 929-5792, rwhitman@usgs.gov
United States Geological Survey, Great Lakes
Science Center, Lake Michigan Ecological Research Station, 1100 North Mineral
Springs Road, Porter,Indiana, 46304,USA, Tel: +1 (219) 926-8336, Fax: +1
(219) 929-5792, rwhitman@usgs.gov
United States Geological Survey, Great Lakes
Science Center, Lake Michigan Ecological Research Station, 1100 North Mineral
Springs Road, Porter,Indiana, 46304,USA, Tel: +1 (219) 926-8336, Fax: +1
(219) 929-5792, rwhitman@usgs.gov
Purdue University Calumet, Department of Biological
Sciences, 2200 169 Street, Hammond,Indiana, 46323,USA
Purdue University Calumet, Department of Biological
Sciences, 2200 169 Street, Hammond,Indiana, 46323,USA
ABSTRACT
We studied the shoreward and seasonal distribution of E. coli and enterococci
in sand (at the water table) at two southern Lake Michigan beaches—Dunbar
and West Beach (in Indiana). Deep, backshore sand (∼20 m inland) was
regularly sampled for 15 months during 2002–2003. E. coli counts were
not significantly different in samples taken at 5-m intervals from 0–40 m
inland (P=0.25). Neither E. coli nor enterococci mean counts showed any
correlation or differences between the two beaches studied. In laboratory
experiments, E. coli readily grew in sand supplemented with lake plankton,
suggesting that in situ E. coli growth may occur when temperature and natural
organic sources are adequate. Of the 114 sand enterococci isolates tested,
positive species identification was obtained for only 52 (46%), with E.
faecium representing the most dominant species (92%). Genetic characterization
by ribotyping revealed no distinct genotypic pattern (s) for E. coli, suggesting
that the sand population was rather a mixture of numerous strains (genotypes).
These findings indicate that E. coli and enterococci can occur and persist
for extended periods in backshore sand at the groundwater table. Although
this study was limited to two beaches of southern Lake Michigan, similar
findings can be expected at other temperate freshwater beaches. The long-term
persistence of these bacteria, perhaps independent of pollution events,
complicates their use as indicator organisms. Further, backshore sand at
the water table may act as a reservoir for these bacteria and potentially
for human pathogens.
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