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Applied and Environmental Microbiology, August 2003, p. 4714-4719, Vol. 69, No. 8
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.8.4714-4719.2003

Occurrence of Escherichia coli and Enterococci in Cladophora (Chlorophyta) in Nearshore Water and Beach Sand of Lake Michigan{dagger}

Richard L. Whitman, Dawn A. Shively, Heather Pawlik, Meredith B. Nevers, and Muruleedhara N. Byappanahalli*

Lake Michigan Ecological Research Station, United States Geological Survey, Porter, Indiana 46304

Received 7 March 2003/ Accepted 29 April 2003

Each summer, the nuisance green alga Cladophora (mostly Cladophora glomerata) amasses along Lake Michigan beaches, creating nearshore anoxia and unsightly, malodorous mats that can attract problem animals and detract from visitor enjoyment. Traditionally, elevated counts of Escherichia coli are presumed to indicate the presence of sewage, mostly derived from nearby point sources. The relationship between fecal indicator bacteria and Cladophora remains essentially unstudied. This investigation describes the local and regional density of Escherichia coli and enterococci in Cladophora mats along beaches in the four states (Wisconsin, Illinois, Indiana, and Michigan) bordering Lake Michigan. Samples of Cladophora strands collected from 10 beaches (n = 41) were assayed for concentrations of E. coli and enterococci during the summer of 2002. Both E. coli and enterococci were ubiquitous (up to 97% occurrence), with overall log mean densities (± standard errors) of 5.3 (± 4.8) and 4.8 (± 4.5) per g (dry weight). E. coli and enterococci were strongly correlated in southern Lake Michigan beaches (P < 0.001, R2 = 0.73, n = 17) but not in northern beaches (P = 0.892, n = 16). Both E. coli and enterococci survived for over 6 months in sun-dried Cladophora mats stored at 4°C; the residual bacteria in the dried alga readily grew upon rehydration. These findings suggest that Cladophora amassing along the beaches of Lake Michigan may be an important environmental source of indicator bacteria and call into question the reliability of E. coli and enterococci as indicators of water quality for freshwater recreational beaches.

* Corresponding author. Mailing address: United States Geological Survey, Lake Michigan Ecological Research Station, 1100 North Mineral Springs Rd., Porter, IN 46304. Phone: (219) 926-8336. Fax: (219) 929-5792. E-mail: byappan{at}usgs.gov.

{dagger} This article is contribution 1244 of the USGS Great Lakes Science Center.

Applied and Environmental Microbiology, August 2003, p. 4714-4719, Vol. 69, No. 8
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.8.4714-4719.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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