Seasonal Distribution of Pathogens and Indicator Organisms in Biofilms in an Agricultural Watershed

摘要

Monitoring water quality is an essential component of the delivery of safe drinking water. However, current microbial evaluation techniques are neither time-efficient nor cost-effective. Standard techniques monitor for innocuous indicator bacteria, which often do not correlate with pathogen concentrations, and bacterial attachment and survival in biofilms are rarely examined. The presence of pathogens protected in the biofilm matrix is compounded in rural agricultural areas, where both faecal contamination of water sources and the potential of exposure are very high. In this research, we attempt to improve our understanding of pathogen behaviour in agricultural watersheds and evaluate substrate surfaces that could be used for standard protocols to monitor for the presence of pathogens that cause disease and economic losses in rural Canadian water systems and around the world. To do so, we monitored the presence of faecal contamination indicators (Heterotrophic plate counts, faecal coliforms, enterococci, and E. coli) and particular pathogens (Pathogenic E. coli 0157 and Salmonella sp.) in water, sediment, and in biofilms on river and slate rock, wood, sandpaper, and LexanTM in Elk Creek (Fraser Valley, British Columbia, Canada) from December 2005 to December 2006. Faecal indicator concentrations and pathogen presence were evaluated using standard culturing and isolation methods. Results showed that monitoring for bacterial indicator concentrations in water column grab samples greatly underestimated the number of indicator bacteria and pathogens present at each site. The results also showed that water column grab samples, especially during the dry season, were not representative of pathogens present in the watershed. This indicates that biofilms might be the main reservoir of Salmonella sp. and pathogenic E. coli O157 during the summer time when rainfall and manure application is low.