Most probable number methodology for quantifying dilute concentrations and fluxes of Escherichia coli O157:H7 in surface waters.
OBJECTIVE
To better understand the transport and enumeration of dilute densities of Escherichia coli O157:H7 in agricultural watersheds, we developed a culture-based, five tube-multiple dilution most probable number (MPN) method.


RESULTS
The MPN method combined a filtration technique for large volumes of surface water with standard selective media, biochemical and immunological tests, and a TaqMan confirmation step. This method determined E. coli O157:H7 concentrations as low as 0.1 MPN per litre, with a 95% confidence level of 0.01-0.7 MPN per litre. Escherichia coli O157:H7 densities ranged from not detectable to 9 MPN per litre for pond inflow, from not detectable to 0.9 MPN per litre for pond outflow and from not detectable to 8.3 MPN per litre for within pond. The MPN methodology was extended to mass flux determinations. Fluxes of E. coli O157:H7 ranged from <27 to >10(4) MPN per hour.


CONCLUSIONS
This culture-based method can detect small numbers of viable/culturable E. coli O157:H7 in surface waters of watersheds containing animal agriculture and wildlife.


CONCLUSIONS
This MPN method will improve our understanding of the transport and fate of E. coli O157:H7 in agricultural watersheds, and can be the basis of collections of environmental E. coli O157:H7.
Jenkins
M B
MB
USDA-Agriculture Research Service, J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA, USA. michael.jenkins@ars.usda.gov
Endale
D M
DM
Fisher
D S
DS
Gay
P A
PA
D000818:Animals; D001431:Bacteriological Techniques / Q000379:methods; D002417:Cattle; D015169:Colony Count, Microbial / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods*; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D005374:Filtration; D005618:Fresh Water / Q000382:microbiology; D014867:Water / Q000032:analysis*; D014871:Water Microbiology; D014872:Water Movements
D014867:Water