Bacteriophages as Indicators for Enteric Viruses and Public Health Risks in Groundwaters
For more than 100 years, there has been debate among microbiologists and public health practitioners concerning the role of drinking water monitoring for either pathogens or indicators. By the 1890s, it was generally accepted that monitoring for specific pathogens was not in the best interest of public health protection because there were too many pathogens, they were present in very small concentrations, and methods for their detection were not practical. Public health officials decided that monitoring would be conducted to detect fecal pollution and not for individual pathogens.
Escherichia coli became the primary indicator of fecal pollution at the time. Because methods for the specific detection and identification of E. coli were not well developed, an E. coli surrogate – the total coliform group – was developed. Its detection was based on the physiological observation that the fermentation of lactose in a growth medium that allowed the manifestation of only enteric bacteria would elucidate E. coli and its relatives, the total coliforms. Shortly thereafter, coliform monitoring became codified throughout the world. Coliform monitoring, being rapid, inexpensive, and easy to perform, proved effective. There are low rates of waterborne bacterial disease outbreaks in developed countries today.
Beginning in the 1970s, the role of drinking water transmission of enteric viruses became a subject for concerted studies. It was found that coliforms might differ biologically from the fate of animal viruses in drinking water.
Practicing microbiologists in Europe and the United States (Dr. Henri LeClerc, Institut Pasteur de Lille; Dr. Steve Edberg, Yale University; Jean Marie Delattre, Faculte de medecine de Lille) collaborated to write a peer-reviewed paper that frames the issues regarding the use of bacteriophages as indicators of fecal pollution. The review summarizes the basic strengths and weaknesses of bacteriophages as indicators and clearly frames the questions that need to be answered before bacteriophages can be accepted in the regulatory framework.
Major Findings and Significance
Overall, the conclusion with regard to monitoring for enteric viruses is much the same as that decided by public health officials in the 1890’s. To protect the public’s health, it is better to monitor for the indicators of fecal pollution rather than for specific pathogens. The overriding rationale for this conclusion is that there are still unknown (and simply too many) enteric viral pathogens.
Moreover, they are present in low concentrations, often requiring the analyst to examine more than 10 liters of water. Although methods have been pro- posed for many of the enteric viruses, they are generally quite expensive, tech- nically demanding, and time consuming. From distribution water, where the strategy is to detect relatively recent fecal contamination events, E. coli and total coliforms are the most useful because they can be monitored frequently and inexpensively with easy-to-do, specific tests.
For groundwater, while this strategy has proven effective, the situation is compounded. Here, the infectious particle must travel throughout the aquifer or subterranean water source. Because viruses are smaller than bacteria, there has been concern that the transit times of the bacterial indicators may not be equivalent to those of the human enteric viruses. Moreover, there has been some work indicating that some viral pathogens may be differently resistant to environmental conditions, sewage or water treatment processes, compared to coliform organisms. There are circumstances in which viruses may survive in the water environment when indicator fecal bacteria do not. Accordingly, with recent developments in the ability to detect enteric viral pathogens and viral surrogates, it is appropriate to consider how best to monitor for enteric viruses in groundwater.
This scientific review considers both direct detection methods, and primarily, the proposed viral surrogate and fecal indicators, the bacteriophage. The review found that low concentrations of all types of bacteriophages in groundwater limit their power to predict the presence of enteric viruses. There is little concordance in the literature regarding phage detection methods, thus making comparisons extremely difficult. Different authors have used different hosts, phage concentration methods, and end-point determinations. Also, markedly different volumes of sample have been employed, varying from 1 liter to 400 liters. In addition, bacteriophage concentration methods are not reproducible. Moreover, there is no consensus on the best bacterial host strain, and there is a lack of consistent recovery of bacteriophages from individual fecal specimens. While bacteriophages may be appealing as indicators of groundwater enteric virus pollution, their use is premature at this time and a number of critical issues must be addressed in order for them to meet minimum regulatory requirements.
LeClerc, H., Edberg, S.C., Pierzo, V. and Delattre, J.M., Bacteriophages as Indicators of Enteric Viruses and Public Health Risk in Groundwaters, Journal of Applied Microbiology 88(1).