Persistence of verocytotoxin-producing Escherichia coli O157 : H7 in calves kept on pasture and in calves kept indoors during the summer months in a Swedish dairy herd

In 1997. a Swedish dairy farm was implicated in a human case of veroeytotox igenic Escherichia coli (VTEC) infection. The bacterium was found in a faec al sample from the human case and in faecal samples from cattle on the farm . Subtyping with pulsed field gel electrophoresis (PFGE) showed that the is olates were identical. The farm was further studied to assess the occurrenc e and the epidemiology of the agent at the farm level. The objective of this part of the study presented here was to examine the p ersistence of VTEC O157:H7 in calves that were kept on pasture and indoors, respectively, during the summer. Twelve calves in the herd, with one posit ive faecal sample each of VTEC O157:H7 in April 1999. were followed by faec al sampling during the summer months. Six calves were kept indoors and six were kept on pasture. Faecal samples from each calf were collected once a m onth on five occasions from April to September. Bacterial examination was p erformed with immunomagnetic separation (IMS) and cultivation on CT-SMAC. P CR was used to test for the presence of genes encoding for verocytotoxin (V T). intimin (eaeA). enterohemorrhagic E. coli-hemolysin (EHEC-Hly) and the flagellar antigen H7. PFGE was used for genotyping the isolates. The faecal samples from the calves kept on pasture were negative during the whole period, it is possible that the faecal samples had bacterial counts: lower than the detection limits fur our procedure. or that the faecal samp les were free from the bacteria at the time of sampling. This suggests that calves: on pasture may be less exposed to the bacteria or that they clear themselves. In the pen group, there were between one and six culture positive individua ls per sampling occasion. One of the calves that was housed indoors was pos itive in fat cal culture on four consecutive samplings. (C) 2001 Elsevier S cience B.V. All rights reserved.