Detecting fecal bacteria in surface waters - a study in the southeastern United States advances the research

Authors: Jenkins, Michael; Endale, Dinku; FISHER, DWIGHT - Retired ARS Employee

Submitted to: Resource
Publication Type: Popular Publication
Publication Acceptance Date: 5/1/2012
Publication Date: 7/1/2012
Citation: Jenkins, M., Endale, D.M., Fisher, D.S. 2012. Detecting fecal bacteria in surface waters - a study in the southeastern United States advances the research. Resource: Engineering & Technology for a Sustainable World. 19(4):8-9.

Interpretive Summary: Watersheds with animal feeding operations, grazing herds of beef cattle or sheep, croplands fertilized with manure, and wildlife can pose public health risks by contaminating surface waters with fecal-borne pathogens such as Salmonella and toxigenic E. coli (E. coli 0157:H7). To assess these risks, health officials currently test for fecal bacteria such as non-pathogenic E. coli or fecal enterococci as indicators because tests for the real pathogens are prohibitively expensive or unavailable. Surface water concentrations of E. coli greater than an established maximum are considered indicative of likely contamination with human pathogenic microorganisms. Unfortunately the association between the pathogens and the indicator bacteria is not strong enough to make definitive statements about the safety, or risk, in any particular case. Practical methods are needed to accurately measure the low, but infective, concentrations and the survival (die-off) rates of the pathogens themselves. Researchers at the USDA-ARS in Watkinsville, GA came up with a way to detect pathogens such as Salmonella and toxigenic E. coli (E. coli 0157:H7) in water at levels much lower than previously accomplished. By combining the new approach with a patented (by 1st author) “sentinel chamber” technology the researchers were able to determine comparative die-off rates of these zoonotic pathogens and fecal indicator bacteria in water and soil. Over a period of 2.5 years the researchers collected monthly samples from a perennial stream flowing into a pond, water within the pond, and pond outflow. Concentrations of Salmonella ranging from 0.1 to 120 microbes per liter and E. coli 0157:H7 concentrations ranging from 0.1 to 960 microbes per liter were measured. The researchers also showed that a known toxigenic strain of E. coli 0157:H7 died off more slowly than environmental isolates of E. coli and fecal enterococci. The results demonstrated that the pathogen showed greater persistence than the indicator bacteria, and further indicated the presence of small concentrations of these pathogens. These approaches should be of interest to regulating agencies and researchers across many disciplines.

Technical Abstract: Watersheds with animal feeding operations, grazing herds of beef cattle or sheep, croplands fertilized with manure, and wildlife can pose public health risks by contaminating surface waters with fecal-borne pathogens such as Salmonella and toxigenic E. coli (E. coli 0157:H7). To assess these risks, health officials currently test for fecal bacteria such as non-pathogenic E. coli or fecal enterococci as indicators because tests for the real pathogens are prohibitively expensive or unavailable. Surface water concentrations of E. coli greater than an established maximum are considered indicative of likely contamination with human pathogenic microorganisms. Unfortunately the association between the pathogens and the indicator bacteria is not strong enough to make definitive statements about the safety, or risk, in any particular case. Practical methods are needed to accurately measure the low, but infective, concentrations and the survival (die-off) rates of the pathogens themselves. Researchers at the USDA-ARS in Watkinsville, GA came up with a way to detect pathogens such as Salmonella and toxigenic E. coli (E. coli 0157:H7) in water at levels much lower than previously accomplished. By combining the new approach with a patented (by 1st author) “sentinel chamber” technology the researchers were able to determine comparative die-off rates of these zoonotic pathogens and fecal indicator bacteria in water and soil. Over a period of 2.5 years the researchers collected monthly samples from a perennial stream flowing into a pond, water within the pond, and pond outflow. Concentrations of Salmonella ranging from 0.1 to 120 microbes per liter and E. coli 0157:H7 concentrations ranging from 0.1 to 960 microbes per liter were measured. The researchers also showed that a known toxigenic strain of E. coli 0157:H7 died off more slowly than environmental isolates of E. coli and fecal enterococci. The results demonstrated that the pathogen showed greater persistence than the indicator bacteria, and further indicated the presence of small concentrations of these pathogens. These approaches should be of interest to regulating agencies and researchers across many disciplines.