Erratum
During the relabelling of Figure 1 an error was introduced. The correct figure appears below.
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary-alt:20160716044652-68908-mediumThumb-S0950268807009880_fig1g.jpg?pub-status=live)
Fig. 1. Chemical structure of the tetrasaccharide repeat units in the O-antigens of S. flexneri serotypes 1a and 1c. d-GlcNAc, N-acetylglucosamine; Rha, rhamnose.
The Press apologizes to the authors and readers for this error.