The suitability of traditional microbial indicators (i.e., Escherichia coli and enterococci) has been challenged due to the lack of correlation with pathogens and evidence of possible regrowth in the natural environment. In this study, the relationships between alternative microbial indicators of potential human fecal contamination (Bacteroides thetaiotaomicron, Methanobrevibacter smithii, human polyomaviruses [HPyVs], and F؉ and somatic coliphages) and pathogens (Salmonella spp., Pseudomonas aeruginosa, rotavirus, astrovirus, norovirus GI, norovirus GII, and adenovirus) were compared with those of traditional microbial indicators, as well as environmental parameters (temperature, conductivity, salinity, pH, dissolved oxygen, total organic carbon, total suspended solids, turbidity, total nitrogen, and total phosphorus). Water samples were collected from surface waters of urban catchments in Singapore. Salmonella and P. aeruginosa had significant positive correlations with most of the microbial indicators, especially E. coli and enterococci. Norovirus GII showed moderately strong positive correlations with most of the microbial indicators, except for HPyVs and coliphages. In general, high geometric means and significant correlations between human-specific markers and pathogens suggest the possibility of sewage contamination in some areas. The simultaneous detection of human-specific markers (i.e., B. thetaiotaomicron, M. smithii, and HPyVs) with E. coli and enterococcus supports the likelihood of recent fecal contamination, since the human-specific markers are unable to regrow in natural surface waters. Multiple-linear-regression results further confirm that the inclusion of M. smithii and HPyVs, together with traditional indicators, would better predict the occurrence of pathogens. Further study is needed to determine the applicability of such models to different geographical locations and environmental conditions.
Indicator bacteria, such as Escherichia coli and enterococci (ENT), have been used extensively in past decades to indicate the presence of human enteric pathogens because of the great diversity of pathogens, the large volumes required, and the difficulty in concentrating the typically low concentrations of pathogens from water samples. In Singapore, microbial water quality guidelines for recreational freshwater currently target enterococci (less than 200 counts per 100 ml for 95% of the time).Despite the wide use of fecal indicator bacteria in microbial water quality monitoring, their suitability to represent a level of health risk is still being questioned. One of the reasons is the lack of data correlating the presence and concentrations of the indicators with the presence of disease-associated pathogens. With improvements in microbiological test methods and bacterial species identification, there is growing evidence that fecal indicator bacteria, including E. coli and ENT, do not necessarily correlate well with some of the enteric pathogens, particularly viruses (1). There is also evidence that E. ...