title: Water potential changes in faecal matter and Escherichia coli survival.
abstract: OBJECTIVE
  This study investigated the influence of a range of evaporation rates (2.0, 5.3 and 7.4 mm day(-1)) on degradation of E. coli (ATCC Strain 25922) inoculated in canine faeces.
  
  
  RESULTS
  Experiments were carried out in an environmental chamber and a first order exponential decay function (Chick's Law) was used to estimate degradation rates. We estimated die-off coefficients using linear regression. Die-off rates were -0.07, -0.22 and -0.23 h(-1), respectively, for evaporation rates of 2.0, 5.3 and 7.4 mm day(-1) (P = 0.000+, for each model). Nearly complete die-off was found within 15-60 h (7.4-2.0 mm day(-1) evaporation rates), which corresponds with a water potential of approximately -22.4 MPa.
  
  
  CONCLUSIONS
  This study indicates that canine faeces need not be desiccated to achieve complete loss of indicator organisms. Water potential, which is a combination of osmotic and matric potential, is a key stress that increases as evaporation removes water from the faecal matrix and increases concentration of the remaining faecal solution. Evaporation may remove populations of indicator organisms in faeces relatively quickly, even though faeces are not completely dehydrated.
  
  
  CONCLUSIONS
  This research may be used as the foundation for studies more closely resembling real-world evaporation conditions including diurnal fluctuations, rewetting and freezing.
authors.affiliation: College of Agriculture, Biotechnology and Natural Resources, University of Nevada, Reno, NV 89557, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Garfield
authors.forename: M J
authors.initials: MJ
authors.lastname: Walker
mesh_terms: D000818:Animals; D001673:Biodegradation, Environmental; D015169:Colony Count, Microbial; D003890:Desiccation; D004285:Dogs; D004463:Ecology / Q000379:methods; D004783:Environmental Microbiology; D004926:Escherichia coli / Q000502:physiology*; D005243:Feces / Q000382:microbiology*; D050296:Microbial Viability; D013995:Time