Similar to the reactivity observed for mAbs, most polyclonal antisera

showed a lower reactivity with LaiMut, except some antisera against members of serogroups Icterohaemorrhagiae, Canicola, and Sarmin, which were increased (Table 1). The reaction of the mAbs and polyclonal antisera suggested a substantial change in the profile of the immunoreactive epitopes present on the LaiMut lipopolysaccharide as compared with the parent LaiWT strain. Proteinase K-treated whole-cell lysates of LaiWT and LaiMut were resolved by discontinuous SDS-PAGE and stained. The profiles of both LaiWT and LaiMut were similar, with the exception of a reproducible reduction in the molecular mass of the upper band in the lipopolysaccharide

profile PFT�� CDK inhibitor of LaiMut by approximately 3 kDa in comparison with the wild-type strain (Fig. 1). The reactivity of the F70C7 mAb with LaiMut and LaiWT was evaluated by Western blot analysis. The mAb F70C7 reacted with LaiWT lipopolysaccharide, showing a smear over a range corresponding to 22–60 kDa, a profile consistent with the previously reported reactivity of other anti-lipopolysaccharide mAbs (Jost et al., 1988) (Fig. 2). By contrast, no reaction with the LaiMut lipopolysaccharide was detected; this result is consistent with the low MAT titre measured for F70C7 against LaiMut (Fig. 2). A series of oligonucleotide primers for sequencing the lipopolysaccharide biosynthesis locus was designed using the L. interrogans serovar Lai genome sequence as a reference (Ren et al., 2003). The sequence for both LaiMut and LaiWT was determined for the coding regions LA1626–LA1667 (chromosome 1: bases 1 621 069–1 667 280). In this region, only a Tolmetin single nucleotide difference was identified between the LaiMut and the LaiWT sequence; with reference to the Lai genome sequence, the difference was a T to A base change at base 1 645 132 (Fig.

3). This change is located within LA1647, a 1263 base ORF encoding a putative undecaprenyl-galactosyltransferase. The single base change resulted in an internal inframe stop at amino acid 135 of 420. This report describes a leptospiral lipopolysaccharide mutant from serovar Lai. The approach of using a mAb directed at a determinant found on the lipopolysaccharide to select for escape mutant differs from previous studies that have used polyclonal sera recognizing multiple epitopes for selection. The serological characterization of the LaiMut strain revealed that its mAb-binding profile had altered substantially from the parent strain, with several mAbs no longer able to bind. Furthermore, there was a substantial decrease in MAT titres to the polyclonal antisera not only against the same serogroup but also with cross-reactive antisera against related serogroups (Table 1).