Low expression of AcrB in the deoxycholate-sensitive strains of Salmonella enterica subspecies enterica serovar Pullorum

ABSTRACT We investigated the mechanism responsible for bile susceptibility in three deoxycholate‐sensitive (DCs) strains of Salmonella enterica subspecies enterica serovar Pullorum isolated in 1958 in Japan. Of the genes encoding the AcrAB–TolC efflux system, the expression of acrB mRNA was 10‐fold lower in the DCs strains than in a deoxycholate‐resistant (DCr) strain, whereas those of the acrA and tolC genes were two‐fold lower. These results suggested that low expression of acrB was strongly correlated with bile susceptibility in the DCs strains. In addition, the increase in tolC expression levels was not detected in the DCr mutants derived from the DCs strains, suggesting that difference in the expression levels of tolC is not associated with bile susceptibility.