Sources of Bacteria on Chicago Beaches

The 63rd Street Beach, Chicago, has experienced frequent exceedances of recreational water quality Escherichia coli (E. coli) standards, has a large resident seagull population, and few other potential sources of these bacteria. Enterococci numbers have rarely been determined for this beach. The purpose of this study was to evaluate the relation between E. coli and enterococci populations in seagulls and those in water and sediments at the beach.

To accomplish this goal, E. coli DNA fingerprints and the responses of enterococci to various physiological tests were used to determine similarities in E. coli isolates from seagull feces, beach water and beach sediments for two dates. Temporal variability in E. coli and enterococci isolates from seagulls was observed. Results indicate that seagulls contribute to E. coli populations in water and sediment at the 63rd Street Beach, but that other sources of these bacteria were also likely. This study shows the value of bacterial DNA-fingerprinting, combined with other approaches, to determine effective management strategies for Great Lakes beaches. The results will be of interest to scientists, regulatory agencies, and resource managers.