Application of enterococci antibiotic resistance patterns for contamination source identification at Huntington Beach, California

Huntington Beach, California, one of the most popular surfing spots in the world, is plagued by sporadic, elevated levels of fecal bacteria. To assist with pollution source identification, we analyzed antibiotic resistance patterns (ARPs) of enterococci from four known sources (bird feces, urban runoff, coastal marsh sediment and sewage effluent from local sanitation district) and one unknown source (seawater) using seven antibiotics at four concentrations each. Of 2491 enteroccoci tested, all were resistant to at least one antibiotic at some level. Discriminant analysis indicated that the average correct classification rates for bird feces and urban runoff sources were above 80%. Sewage effluent contained mixed fecal sources. Sixty-four percent of the sewage isolates classified with the sewage category, while the other 35% of isolates were assigned evenly across the other three categories. When enterococci isolated from the seawater were classified using the known ARP database, it was evident that bird feces were the source of surf zone contamination on some days while the coastal salt marsh and sewage plume may have impacted the surf zone water quality to various degrees during other times.