Sequential gene loss promotes expansion of monophasic Salmonella Typhimurium ST34.

Sequential gene loss in monophasic Salmonella Typhimurium ST34 underpins its clonal expansion as a prevalent zoonotic lineage.

• Why it matters: Understanding how pathogenic bacterial variants expand is crucial for predicting and controlling infectious disease outbreaks. The mechanisms behind the emergence of specific bacterial lineages remain poorly understood, limiting effective intervention strategies.
• What they did: The study analyzed 44,597 Salmonella Typhimurium genomes and conducted functional and in vivo competition experiments, revealing that a frameshift mutation in dinB causes transcriptional changes that affect flagellin gene expression and gut infection requirements.
• The result: Findings support a stepwise pathoadaptation model where gene loss events in a specific order facilitated mSTM ST34's global spread, offering mechanistic insights for forecasting future pandemics.