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Decay of Fecal Indicator Bacteria and Microbial Source Tracking Markers in Cattle Feces
Oladeinde, A., R. Brown, B. Snyder, K. Bradshaw, T. Bohrmann, C. Wong, AND M. Molina. Decay of Fecal Indicator Bacteria and Microbial Source Tracking Markers in Cattle Feces. Presented at 98th Annual Southeastern American Society for Microbiology Meeting, Athens, GA, October 25 - 27, 2012.
The survival of fecal indicator bacteria (FIB) and microbial source tracking (MST) markers in water microcosms and manure amended soils has been well documented; however, little is known about the survival of MST markers in bovine feces deposited on pastures. We conducted a study to determine the decay rates of FIB and real- time quantitative PCR (qPCR) genetic markers specific for fecal bacteria in 18 freshly deposited cattle fecal samples from three farms in North Georgia. Fecal samples were randomly assigned to shaded and unshaded treatments. A log linear model was employed to characterize the decay exhibited by E.coli, Enterococci and a cow-specific genetic marker (cowM3). Shading significantly decreased the decay rate of E.coli (P<0.0006) which exhibited a T90 of 29 days for the shaded treatment, while the unshaded treatment had a T90 of 16 days. No significant difference due to shading was observed in the decay rates of culturable Enterococci (cE) and the cow–specific marker, which exhibited T90s of 34 and 35 days, respectively under both treatments. E.coli showed re-growth during the first six days after deposition before the decline phase. Moisture content correlated with FIB and cow- specific marker concentrations in both treatments with adjusted R2 values ranging from 0.2 – 0.7 (P< 0.0001). The results of this study indicate that the cow-specific marker can last for up to a month after deposition in the environment; and while its decay dynamic differs from E. coli, it seems a reliable MST marker to use in association with Enterococci for monitoring fecal pollution from pasture lands.