Airborne dissemination of Escherichia coli in a dairy cattle farm and its environment.

There are multiple ways bacteria can be transported from its origin to another area or substrate. Water, food handlers, insects and other animals are known to serve as a vehicle for bacterial dispersion. However, the importance of the air in open areas as a possible way of bacterial dissemination has not been so well analyzed. In this study, we investigated the airborne dissemination of Escherichia coli from the inside of a dairy cattle farm to the immediate environment. The air samples were taken inside the farm (area 0) and from the immediate outside farm surroundings at distance of 50, 100 and 150m in four directions (north, south, east, and west). At each point, the air was collected at different heights: 40cm, 70cm and 1m. The sampling was carried out in two weather seasons (November and July). E. coli was isolated in both inside and outside air, even in samples taken 150m from the farm. A seasonal effect was observed with more bacterial isolates when temperature was higher. Regarding the distribution of the isolates, wind direction appeared as a determining factor. In order to verify that E. coli strains isolated from animal housing facilities were identical to those isolated from the air of the immediate farm environment, their genomic DNA profiles were analyzed by pulsed-field gel electrophoresis (PFGE) after digestion with the endonuclease XbaI. The comparison of genetic profiles suggested that the strains isolated from inside and outside the farm were related, leading to the conclusion that the air is an important vehicle for E. coli dissemination.