BEACHNET==> new article in Water Research

[Katarzyna Przybyla-Kelly <kprzybyla-kelly@usgs.gov>]

doi:10.1016/j.watres.2008.11.012

Copyright © 2008 Elsevier Ltd All rights reserved.

Seasonal stability of Cladophora-associated Salmonella in Lake Michigan watersheds

Muruleedhara N. Byappanahalli^a, Richard Sawdey^b, Satoshi Ishii^b, Dawn A. Shively^a, John A. Ferguson^b, Richard L. Whitman^a and Michael J. Sadowsky^{b, c, , ,}

^aUnited States Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, Porter, IN 46304, USA

^bDepartment of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA

^cBiotechnology Institute, University of Minnesota, St. Paul, MN 55108, USA

Received 5 September 2008;  revised 10 November 2008;  accepted 12 November 2008.  Available online 21 November 2008.
Abstract

The bacterial pathogens Shigella, Salmonella, Campylobacter, and shiga toxin-producing E. coli (STEC) were recently found to be associated with Cladophora growing in southern Lake Michigan. Preliminary results indicated that the Salmonella strains associated with Cladophora were genetically identical to each other. However, because of the small sample size (n = 37 isolates) and a lack of information on spatial–temporal relationships, the nature of the association between Cladophora and Salmonella remained speculative. In this study, we investigated the population structure and genetic relatedness of a large number of Cladophora-borne Salmonella isolates from Lake Michigan (n = 133), as well as those isolated from stream and lake water (n = 31), aquatic plants (n = 8), and beach sands and sediments (n = 8) from adjacent watersheds. Salmonella isolates were collected during 2005–2007 between May and August from Lake Michigan beachsheds in Wisconsin, Illinois, and Indiana. The genetic relatedness of Salmonella isolates was examined by using the horizontal, fluorophore-enhanced rep-PCR (HFERP) DNA fingerprinting technique. While the Salmonella isolates associated with Cladophora exhibited a high degree of genetic relatedness (≥92% similarity), the isolates were not all genetically identical. Spatial and temporal relationships were evident in the populations examined, with tight clustering of the isolates both by year and location. These findings suggest that the relationship between Salmonella and Cladophora is likely casual and is related to input sources (e.g. wastewater, runoff, birds) and the predominant Salmonella genotype surviving in the environment during a given season. Our studies indicate that Cladophora is likely an important reservoir for Salmonella and other enteric bacterial pathogens in Lake Michigan beachsheds, which in turn may influence nearshore water quality.

Keywords: Beach water quality; Cladophora–Salmonella association; Enteric bacteria; Environmental survival; Lake Michigan; Public health

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Kasia Przybyla-Kelly
USGS, Biological Resource Division
Lake Michigan Ecological Research Station
1100 N Mineral Springs Rd.
Porter, IN 46304
219-926-8336 Ext. 423
kprzybyla-kelly@usgs.gov