Germs and Geology: Emerging Issues in Waterborne Pathogen Research
Prof. Larry McKay, 2008 Birdsall-Dreiss Lecturer, Department of Earth and Planetary Sciences, University of Tennessee
This lecture will address how recent hydrological research and development of new analytical methods in molecular microbiology can combine to change how we detect, monitor and predict the exposure of human populations to waterborne pathogens. Much of our understanding of waterborne pathogen occurrence and transport is based on conceptual models and investigative methods that have changed little in the past 30-50 years. Traditional paradigms for waterborne pathogens can be described with terms as simple as coliforms=pathogen-risk, surface-water=bad, groundwater=good, karst=bad, sand=good, true-groundwater=good, and groundwater-under-the-direct-influence-(GWUDI)-of-surface-water=bad. Recent investigations at UT and many other institutions challenge the existing paradigms. For example, a study of community water supply wells in karst aquifers in east Tennessee indicated that enteric viruses are common and can occur even in wells that don’t exhibit other indicators of fecal contamination. Other studies at UT show that very rapid transport of bacteria and viruses can occur in fractured clay-rich sediments and in partially-saturated soils, both of which are settings where slow transport of pathogens is usually expected. There is a great need for additional field-based studies of pathogen occurrence and transport, as well as better collaboration between hydrologists, microbiologists and the public health community. Development of faster or easier to use microbial assays, as well as better sample collection and concentration methods, are providing hydrological researchers with improved tools to help carry out this research. Chief amongst these tools is the development of molecular assays, such as qPCR, which detect pathogens or other fecal microorganisms based on their DNA or RNA signature. Investigators at UT have developed a series of qPCR assays for Bacteroides (a major constituent of feces), which can be used to rapidly and inexpensively determine both the fecal concentration in a water sample and the likely source (human, cattle, horse, etc.). These assays have been used to delineate contaminant sources in watershed studies and have the potential for use in field experiments, allowing bacteria from different fecal sources to be traced throughout a flow system.