Cluster analysis of L. interrogans serovar Lai rfb genes. The subset of 89 rfb genes in microarray was used to generate a dendrogram of strains based on the presence or absence of the genes. The strains were grouped by average hierarchical clustering using the CLUSTER program and the output displayed using the TREEVIEV program. Shown at the top is the unrooted tree for the relationship of the serovars. Red and black areas denote the presence and absence of genes respectively.