Impaired acid stress resistance in Salmonella Typhi Ty2.

Salmonella Typhi exhibits significantly impaired acid stress resistance compared to Salmonella Typhimurium, with growth suppressed at pH 4.5 due to gene loss.

• Why it matters: Understanding acid stress resistance is crucial because it enables Salmonella to survive gastrointestinal transit and macrophage environments, influencing infection and disease progression. The limited knowledge about S. Typhi's mechanisms hampers insights into typhoid fever pathogenesis.
• What they did: Researchers compared growth and gene expression of S. Typhimurium and S. Typhi at various pH levels, identifying differentially expressed acid-induced genes and assessing their roles through targeted gene deletions and heterologous gene expression.
• The result: Findings reveal that S. Typhi's loss of key membrane proteins, regulators, and stress response genes—due to pseudogenization—reduces its acid tolerance, highlighting evolutionary divergence impacting its pathogenic capacity.