Long-term survival of Escherichia coli O157:H7 and Salmonella Typhimurium in cowpats on pasture.

Abstract

To investigate the survival of Escherichia coli O157:H7 and Salmonella Typhimurium in cowpats on pasture in a temperate Nordic climate. The study consists of two parts, the first part using artificially created cowpats inoculated with E.coli O157:H7 and S. Typhimurium and the second part using cowpats from empty pastures on which cattle herds positive for E.coli O157:H7 had grazed 6month previously. Artificial cowpats were created, placed in an outdoor field station in June, August and October, and sampled over 1year. Escherichia coli O157:H7 and S. Typhimurium were analysed by standard culture methods. The results showed viable E.coli O157:H7 and S. Typhimurium in the sampled cowpats throughout the 365-day sample period for the June trial, 250days for the August trial and 40-70days for the October trial. In addition, 200 natural cowpats were sampled from eight pastures that had previously held E.coli O157:H7 positive cattle herds. Five positive E.coli O157:H7 isolates were obtained, all with the same multi-locus variable number tandem repeat analysis pattern as had been found on the pasture the previous grazing season. Escherichia coli O157:H7 and S. Typhimurium can survive in cowpats up to a year and persist throughout a winter season. Therefore, there is a possibility that cowpats can act as a reservoir and be a source of re-infection of Salmonella or E.coli O157:H7 in cattle between grazing seasons. The obtained results can provide valuable information for managing the risk posed by zoonotic pathogens originating from farm environments.