Genetic diversity and population structure of Escherichia coli from neighboring small-scale dairy farms.

The genetic diversity and population structure of Escherichia coli isolates from small-scale dairy farms were used to assess the ability of E. coli to spread within the farm environment and between neighboring farms. A total of 164 E. coli isolates were obtained from bovine feces, bedding, cow teats and milk from 6 small-scale dairy farms. Ward's clustering grouped the isolates into 54 different random amplified polymorphic DNA (RAPD) types at 95% similarity, regardless of either the sample type or the farm of isolation. This suggests that RAPD types are shared between bovine feces, bedding, cow teats, and milk. In addition, transmission of RAPD types between the studied farms was suggested by the Ward grouping pattern of the isolates, Nei's and AMOVA population analyses, and genetic landscape shape analysis. For the first time, the latter analytical tool was used to assess the ability of E. coli to disseminate between small-scale dairy farms within the same producing region. Although a number of dispersal mechanisms could exist between farms, the genetic landscape shape analysis associated the flow of E. coli RAPD types with the movement of forage and milking staff between farms. This study will aid in planning disease prevention strategies and optimizing husbandry practices.