Survival and spread of Shiga toxin-producing Escherichia coli in alpine pasture grasslands
Résumé
Aims: To determine the fate of Shiga toxin-producing Escherichia coli (STEC) strains defecated onto alpine grassland soils. Methods and Results: During the summers of 2005 and 2006, the field survival of STEC was monitored in cowpats and underlying soils in four different alpine pasture units. A most probable number (MPN)-PCR stx assay was used to enumerate STEC populations. STEC levels ranged between 3Æ9 and 5Æ4 log10 CFU g)1 in fresh cowpats and slowly decreased until their complete decay (inactivation rates k < 0Æ04 day)1). PFGE typing of STEC strains isolated from faecal and soil samples assessed the persistence of various clonal types for at least 2 months in cowpats and their vertical dispersal down through the soil at a depth up to at least 20 cm. STEC cells counts in soil were always below 2 log10 CFU g)1, regardless of the pasture unit investigated. The soil became rapidly free of detectable STEC once the cowpat had decomposed. The eight STEC strains isolated during this study belonged to six distinct serotypes and tested positive for the gene(s) stx2, including the stx2g and stx2 NV206 variants. Conclusions: STEC were able to persist in cowpats and disseminate down through the soil but were unable to establish. Significance and impact of the Study: This study provides useful information concerning the ecology of STEC in alpine pasture grasslands and may have implications for land and cattle management.