This study examined the ecology of Rhodococcus coprophilus, a nocardioform actinomycete previously isolated from freshwater environments. The researchers demonstrated that R. coprophilus reaches very high numbers in cattle dung and can survive passage through the ruminant digestive system without actively growing there. The organism colonizes pasture grass and hay used as fodder, where it survives desiccation and environmental stress. When cattle excrete R. coprophilus-laden feces, the organism is washed from pastures into streams and rivers, accumulating in sediments and lake muds. The authors identified R. coprophilus in high numbers in streams receiving drainage from dairy farms, contrasting with low numbers in unpolluted streams where other actinomycetes predominate. The study also isolated bacteriophages attacking R. coprophilus from aged cow manure, indicating active growth in dung. The researchers concluded that R. coprophilus cycles through grazing animals and agricultural environments, potentially serving as an indicator organism for detecting dairy farm effluent contamination in water systems.

Key findings

• R. coprophilus grows actively in aged cattle dung and survives desiccation and winter conditions, serving as a reservoir of infection
• The organism survives passage through the ruminant digestive system without establishing active rumen populations, indicating external dietary origin
• High numbers of R. coprophilus in streams correlate with dairy farm drainage discharge, suggesting utility as a pollution indicator
• Pasture grass and hay contaminated with R. coprophilus provide the primary route of exposure for grazing herbivores
• The organism cycles from soil and grass through animal feces to freshwater sediments, establishing a predictable ecological pathway