A dam mutant of Yersinia pestis is attenuated and induces protection against plague.

We have constructed a dam mutant of Yersinia pestis GB. In BALB/c mice inoculated subcutaneously, the median lethal dose of the mutant was at least 2000-fold higher than the wild type. Mice inoculated with sub-lethal doses of the mutant were protected against a subsequent challenge with virulent Y. pestis. The effect of dam inactivation on gene expression was examined using a DNA microarray, which revealed increased expression of a number of genes associated with the SOS response. These results confirm the key role of Dam in the regulation of virulence, and its potential role as a target for the generation of attenuated strains of pathogenic bacteria.