Oral immunization with a dam mutant of Yersinia pseudotuberculosis protects against plague

Abstract

Inactivation of the gene encoding DNA adenine methylase (dam) has been shown to attenuate some pathogens such asSalmonella entericaserovar Typhimurium and is a lethal mutation in others such asYersinia pseudotuberculosisstrain YPIII. In this study thedammethylase gene inYersinia pseudotuberculosisstrain IP32953 was inactivated. Unlike the wild-type, DNA isolated from the mutant could be digested withMboI, which is consistent with an altered pattern of DNA methylation. The mutant was sensitive to bile salts but not to 2-aminopurine. The effect ofdaminactivation on gene expression was examined using a DNA microarray. In BALB/c mice inoculated orally or intravenously with thedammutant, the median lethal dose (MLD) was at least 106-fold higher than the MLD of the wild-type. BALB/c mice inoculated with the mutant were protected against a subcutaneous challenge with 100 MLDs ofYersinia pestisstrain GB and an intravenous challenge with 300 MLDs ofY. pseudotuberculosisIP32953.