Quantitative Evaluation of Enterococci and Bacteroides Released by Adults and Toddlers in Marine Water

Traditionally the use of enterococci as fecal indicator bacteria (FIB) has been recommended by EPA for testing recreational marine water. Recent studies showed that bathers shed large numbers of enterococci in the water. Two separate studies were conducted to evaluate bather shedding for enterococci using membrane filter (MF), chromogenic substrate (CS), and quantitative polymerase chain reaction (qPCR)) and alternative FIB (e.g. bacteroides human markers via qPCR). The first study consisted of two sets of 10 adults who bathed together in a large pool (first two cycles were without beach sand exposure and the last two cycles were after sand exposures). The second study consisted of 14 sets of toddlers who bathed individually in a small pool which allowed for sand recovery. The numbers of estimated enterococci shed per adult ranged from 1.8x104 to 2.8x106 CFU, 1.9x103 to 4.5x106 MPN, and 3.8x105 to 5.5x106 GEU based on the MF, CS, and qPCR methods respectively. The estimated numbers of bacteroides human markers ranged from 1.8x104 to 1.3x106 for UCD and ranged from the below detection limit to 1.6x105 for HF8. The estimated amount of sand transported per toddler (n=14) into the water column after sand exposure was 8±6 g on average. Contributions of sands to the total enterococci (MF) shed per toddler was 3.7 ±4.4% on average. FIB shedding associated with beach sand could be small fraction during initial bathing but may have a significant role if bathers go to water repetitively after sand exposure.