A study was conducted to determine the reliability and repeatability of ant
ibiotic resistance analysis as a method of identifying the sources of fecal
pollution in surface water and groundwater. Four large sets of isolates of
fecal streptococci (from 2,635 to 5,990 isolates per set) were obtained fr
om 236 samples of human sewage and septage, cattle and poultry feces, and p
ristine waters. The patterns of resistance of the isolates to each of four
concentrations of up to nine antibiotics were analyzed by discriminant anal
ysis. When isolates were classified individually, the average rate of corre
ct classification (ARCC) into four possible types (human, cattle, poultry,
and wild) ranged from 64 to 78%. When the resistance patterns of all isolat
es from each sample were averaged and the resulting sample level resistance
patterns were classified, the ARCCs were much higher (96 to 100%). These d
ata confirm that there are measurable and consistent differences in the ant
ibiotic resistance patterns of fecal streptococci isolated from various sou
rces of fecal pollution and that antibiotic resistance analysis can be used
to classify and identify these sources.