Epidemiology and antimicrobial resistance of Salmonella enterica serotype Infantis in the United States: infections and emergence of a multidrug-resistant strain during 1979–2022

Background Salmonella infections are a major cause of human illness in the United States. Salmonella enterica serotype Infantis has re-emerged as a leading serotype with the emergence of a multidrug-resistant S. Infantis strain, designated as REPJFX01 by the Centers for Disease Control and Prevention (CDC). REPJFX01, which typically contains a megaplasmid of emerging Salmonella Infantis (pESI) harbouring multiple resistance genes and a chromosomal gyrA87 mutation conferring decreased susceptibility to ciprofloxacin, has caused human infections linked to chicken consumption.