The effect of PmrA/B two-component system on the phenotype and virulence of Salmonella Typhimurium

To investigate the role of the PmrA/B two-component system in the pathogenicity of Salmonella Typhimurium, this study constructed single-gene deletion mutants of PmrA and PmrB, a double-gene deletion mutant of PmrA/B, and their corresponding complementary strains using the λ-Red homologous recombination system. The biological characteristics of the wild-type strain, mutant strains, and complemented strains were systematically evaluated. The results confirmed the successful construction of all mutants and complement strains by PCR and sequencing. Growth curve analysis indicated that deletion of PmrA/B did not affect bacterial growth. In antibiotic susceptibility tests, the PmrB and PmrA/B deletion mutants exhibited increased sensitivity to doxycycline and tetracycline, while the PmrA/B mutant also showed enhanced sensitivity to imipenem. Biofilm formation was significantly impaired in the PmrA/B double mutant. Under stress conditions, the PmrA/B mutant displayed reduced tolerance to high osmolarity and acidic environment (pH 4.5). Moreover, adhesion and invasion capabilities were significantly decreased in all mutant strains. Mouse infection experiments demonstrated that the PmrA/B mutant led to significantly lower liver and spleen indices and bacterial loads compared to the wild-type strain. In conclusion, the PmrA/B two-component system is critically involved in biofilm formation, stress resistance, and virulence of Salmonella Typhimurium, providing a theoretical basis for further understanding its pathogenic mechanisms.