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

AIM: To investigate the survival of Escherichia coli O157:H7 and Salmonella Typhimurium in cowpats on pasture in a temperate Nordic climate. METHODS AND RESULTS: 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 6 month previously. Artificial cowpats were created, placed in an outdoor field station in June, August and October, and sampled over 1 year. 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, 250 days for the August trial and 40-70 days 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. CONCLUSIONS: 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. SIGNIFICANCE AND IMPACT OF THE STUDY: The obtained results can provide valuable information for managing the risk posed by zoonotic pathogens originating from farm environments.

Treatment with Ca(OH)2 for inactivation of Salmonella Typhimurium and Enterococcus faecalis in soil contaminated with infected horse manure.

AIM: To investigate the inactivation of Salmonella enterica serovar Typhimurium and the faecal indicator Enterococcus faecalis in horse manure:soil mixtures by application of hydrated lime (Ca(OH)(2)). METHODS AND RESULTS: In laboratory incubations, the inhibitory effect of different concentrations of Ca(OH)(2), as well as different application techniques, was tested. Other variables were horse manure:soil ratio, incubation temperature (6 and 14°C) and soil type (sand/clay). Bacterial enumeration by the plate count method in samples taken at increasing intervals revealed that Ca(OH)(2) effectively reduced Salmonella Typhimurium numbers. However, to achieve a sufficient reduction, the Ca(OH)(2) had to be applied at a sufficient rate, and the amount required varied because of manure:soil ratio and incubation temperature. The results showed that a pH above 11 was needed and that a high pH had to be maintained for up to 7 days. An appropriate application technique for the Ca(OH)(2) was also important, so that a high pH was obtained throughout the whole material to be treated. In addition, a high manure:soil ratio in combination with a higher incubation temperature was found to rapidly neutralize the pH and to increase the risk of Salmonella re-growth. CONCLUSIONS: Application of Ca(OH)(2) can be an efficient method for treating a Salmonella-contaminated horse paddock. A high pH is a key factor in Salmonella inactivation, and thus, monitoring the pH during the treatment period is necessary. To avoid re-growth excess manure should be removed for separate treatment elsewhere. SIGNIFICANCE AND IMPACT OF THE STUDY: Persistence of Salmonella in horse paddocks poses a risk of disease transmission to healthy animals and people who come into contact with these animals. An efficient method to de-contaminate a Salmonella-contaminated soil would be a valuable tool for animal welfare and for public health.