Distributions of enterococci and human-specific bacteriophages of enterococci in a tropical watershed

The bacteriophages of E. faecalis strains AIM06 (DSM100702) and SR14 (DSM100701) have previously been validated as human-specific microbial source tracking (MST) markers in Thailand. In this study, their spatial and temporal distribution in a freshwater river was investigated for the first time (n = 48). The abundance of enterococci as a standard microbial water quality parameter was evaluated by both the qPCR detection assay with primers and a hydrolysis probe according to the US EPA Method 1611 and the US EPA Method 1600 membrane filtration culture method. AIM06 and SR14 phages were detected by a double layer agar assay and were present in 87.5% and 81.3% of all samples with a co-presence of 92.9% of phage-positive samples. After spiking the representative phages, the ranges of recovery efficiencies were 57.9-99.6% and 49.6-99.9% (n = 48) for AIM06 and SR14 phages, respectively. The absolute abundance of AIM06 and SR14 phages ranged from 0.25 to 221.94 and from 0.25 to 76.66 PFU/100 mL, respectively. Enterococci DNA copies and CFU were detected in all samples ranging from 3.24 to 6.32 log10 copies/100 mL and 100.00 to 1593 CFU/100 mL, respectively. Enterococci in the qPCR assay also showed a moderate correlation with the culture method. The AIM06 and SR14 phage results indicated continuing human faecal pollution along the river with no significant different levels among stations. Interestingly, the higher levels of enterococci in downstream stations for both the qPCR and culture methods along with the significant correlation with other faecal indicator organisms and non-human MST markers implied non-human faecal pollution. In conclusion, this study provides insightful information that could lead to effective water quality management and public health risk reduction from exposure to faecally-contaminated water.