2012 Annual Report
1a.Objectives (from AD-416):
The objective of this study is to evaluate TMECC and EPA pathogen detection methods in order to accurately determine the presence of populations of E. coli O157:H7, Salmonella, non-pathogenic E. coli, and fecal coliforms in ‘point of sale’ composts collected from commercial operations across the United States. Correlations between the presence of pathogens and several physico-chemical parameters (moisture, water activity, electrical conductivity, soluble carbon, pH, and carbon:nitrogen ratios) will be investigated.
1b.Approach (from AD-416):
ARS will acquire the basic knowledge about the stresses that pathogenic E. coli or Salmonella strains undergo in compost and their prevalence in various types of compost. The carbon:nitrogen ratio will evaluated in commercial formulations. Based on these findings, compost formulations using specific C:N ratios will then be formulated to determine survival and inhibition of E. coli and Salmonella.
Background testing for E. coli and fecal coliforms by both EPA and U.S. Compost Council methods (TMECC) methods were completed on eight finished, point-of-sale composts. Three of eight samples tested positive for fecal coliforms, and two of these three samples were positive for E. coli. Two of the three levels were above the EPA prescribed levels of 1000 CFU/g for fecal coliform counts in biosolids. Five samples have been inoculated with non-pathogenic E. coli, Salmonella, and E. coli O157:H7 and evaluated using both EPA and TMECC methods. For the five compost samples inoculated with high levels of bacteria, both EPA and TMECC methods had similar recovery rates. It was determined that compost samples inoculated at lower levels would provide a better comparison of the recovery rates of the EPA and TMECC methods.