Growth and survival of non-O157:H7 Shiga-toxin-producing Escherichia coli in cow manure

The main objective of this study was to evaluate the behaviour of non-O157:H7 Shiga-toxin-producing Escherichia coli (STEC) strains in cow manure. A mixture of eight green-fluorescent-protein-labelled STEC strains was inoculated around 10⁶-10⁷ CFU g⁻¹ into four manure heaps. Two heaps were regularly turned and the two others remained unturned. STEC counts and physical parameters (temperature, pH, moisture content and oxido-reduction potential) were monitored for 1000 manure samples. The highest mean pH values were obtained near the surface at the base of all manure heaps. At the surface, the moisture content decreased from 76·5% to 42% in turned heaps. Temperatures reached 65°C near the main body of all manure heaps, and only 35°C near the superficial parts located at the base of them. These two sites (the centre and the base) were associated with D values for the STEC counts of 0·48 and 2·39 days, respectively. We were able to detect STEC strains during 42 days in turned manure heaps and during at least 90 days in unturned ones. These results emphasize the long-term survival of non-O157:H7 STEC in cow manure. Good management practices (e.g. turning) should be respected in order to minimize the risk of environmental contamination by STEC.