Quantitative analysis of human- and cow-specific 16S rRNA gene markers for assessment of fecal pollution in river waters by real-time PCR

The base sequences representing human- and cow-specific 16S rRNA gene markers identified in a T-RFLP analysis were recovered from clone libraries. The human- and cowspecific primers were designed from these sequences and their specificities were analyzed with fecal DNAs from human, cow, and pig. The AllBac primer set showed positive results for all human, cow, and pig samples, whereas the human-specific primer set showed positive result only for the human sample but not for the cow or pig samples. Likewise, the cow-specific primer set showed positive results only for the cow sample but not for the human or pig samples. Real-time PCR assay with these primers was developed for the identification and quantification of fecal pollution in the river water. The human- and cow-specific markers were detected in the order of 9 log₁₀ copies per gram wet feces, which were two orders of magnitude lower than those of total Bacteroidales. For the river water samples, the human-specific marker was detected in 1.7-6.2 log₁₀ copies/100 ml water, which was 2.4-4.9 orders of magnitude lower than those of total Bacteroidales. There was no significant correlation between total Bacteroidales and conventional fecal indicators, but there was a high correlation between Bacteroidales and the human-specific marker. This assay could reliably identify and quantify the fecal pollution sources, enabling effective measures in the watersheds and facilitating water quality management.