Feedlot Layout. Schematic representation of the spatial and chronological distribution of Escherichia coli O157 clusters in this feedlot (see Figure 1). Coloured dots represent the Multi-locus variable number of tandem repeat analysis (MLVA) types. Red lines between pens indicate pen bars and dots on lines indicate the MLVA type exhibited by isolates detected on pen bars or in water troughs between pens. Coloured dots outside the feedlot represent the MLVA types displayed by those strains cultured from slurry tank faecal samples.