Microbial load from animal feces at a recreational beach

Abstract

The goal of this study was to quantify the microbial load (enterococci) contributed by the different animals that frequent a beach site. The highest enterococci concentrations were observed in dog feces with average levels of 3.9 x 10(7) CFU/g; the next highest enterococci levels were observed in birds averaging 3.3 x 10(5)CFU/g. The lowest measured levels of enterococci were observed in material collected from shrimp fecal mounds (2.0 CFU/g). A comparison of the microbial loads showed that 1 dog fecal event was equivalent to 6940 bird fecal events or 3.2 x 10(8) shrimp fecal mounds. Comparing animal contributions to previously published numbers for human bather shedding indicates that one adult human swimmer contributes approximately the same microbial load as one bird fecal event. Given the abundance of animals observed on the beach, this study suggests that dogs are the largest contributing animal source of enterococci to the beach site.

Figure 1

The study beach was located within Biscayne Bay on Virginia Key, east of Miami, Fl. The focus area is identified as the eastern most 360 m. Bottom inset shows location of camera. Boxes within the bottom inset show grid boxes used for in-field visual counting surveys for dogs and humans. Top inset shows transect and plots used for the in-field visual counting surveys for shrimp.

Figure 2

Enterococci concentrations (per gram of dry feces) from feces from different types of birds and the respective sample size in parenthesis. Error bars represent the standard deviation for the respective type of bird within that sample size.