Use of Total Coliform Test for Watershed Monitoring with Respect to Atypicals

A 2-year study was conducted on the relationships between atypical colonies (AC) from total coliform (TC) tests and other bacterial indicators of water quality in a watershed mainly impacted by agricultural and urban animals. Eight representative sites were monitored for TC, feel coliforms (FC) and coliphage (CP) concentrations. Sampling sites included those impacted by raw sewage, agricultural runoff, urban runoff, and a mixture of urban and agricultural runoff. AC were found to be composed of coliforms (about 27%), noncoliforms (37%), and Aeromonas (36%). There was a clear pattern among the atypical concentrations, fecal pollution sources, and pollution levels. Correlation analyses found the densities of AC to be well associated with the densities of FC and not well associated with total CP (RFC = 0.796 and RCP = 0.575, respectively). A reference index defined as the ratio of AC to CP correlated well with degree of fecal pollution known to impact the sites. Results suggest that AC from TC tests using the membrane filter method and M-Endo medium may be used as supplemental indicators in conjunction with other microbial indicators for watershed monitoring.