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<jats:title>ABSTRACT</jats:title> <jats:p>Nontyphoidal <jats:italic>Salmonella</jats:italic> (NTS), particularly <jats:italic>Salmonella enterica</jats:italic> serovar Typhimurium, is among the leading etiologic agents of bacterial enterocolitis globally and a well-characterized cause of invasive disease (iNTS) in sub-Saharan Africa. In contrast, <jats:italic>S</jats:italic>. Typhimurium is poorly defined in Southeast Asia, a known hot spot for zoonotic disease with a recently described burden of iNTS disease. Here, we aimed to add insight into the epidemiology and potential impact of zoonotic transfer and antimicrobial resistance (AMR) in <jats:italic>S</jats:italic>. Typhimurium associated with iNTS and enterocolitis in Vietnam. We performed whole-genome sequencing and phylogenetic reconstruction on 85 human (enterocolitis, carriage, and iNTS) and 113 animal <jats:italic>S</jats:italic>. Typhimurium isolates isolated in Vietnam. We found limited evidence for the zoonotic transmission of <jats:italic>S</jats:italic>. Typhimurium. However, we describe a chain of events where a pandemic monophasic variant of <jats:italic>S</jats:italic>. Typhimurium (serovar I:4,[5],12:i:− sequence type 34 [ST34]) has been introduced into Vietnam, reacquired a phase 2 flagellum, and acquired an IncHI2 multidrug-resistant plasmid. Notably, these novel biphasic ST34 <jats:italic>S</jats:italic>. Typhimurium variants were significantly associated with iNTS in Vietnamese HIV-infected patients. Our study represents the first characterization of novel iNTS organisms isolated outside sub-Saharan Africa and outlines a new pathway for the emergence of alternative <jats:italic>Salmonella</jats:italic> variants into susceptible human populations.</jats:p> <jats:p><jats:bold>IMPORTANCE</jats:bold> <jats:italic>Salmonella</jats:italic> Typhimurium is a major diarrheal pathogen and associated with invasive nontyphoid <jats:italic>Salmonella</jats:italic> (iNTS) disease in vulnerable populations. We present the first characterization of iNTS organisms in Southeast Asia and describe a different evolutionary trajectory from that of organisms causing iNTS in sub-Saharan Africa. In Vietnam, the globally distributed monophasic variant of <jats:italic>Salmonella</jats:italic> Typhimurium, the serovar I:4,[5],12:i:− ST34 clone, has reacquired a phase 2 flagellum and gained a multidrug-resistant plasmid to become associated with iNTS disease in HIV-infected patients. We document distinct communities of <jats:italic>S</jats:italic>. Typhimurium and I:4,[5],12:i:− in animals and humans in Vietnam, despite the greater mixing of these host populations here. These data highlight the importance of whole-genome sequencing surveillance in a One Health context in understanding the evolution and spread of resistant bacterial infections.</jats:p>

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Journal article




American Society for Microbiology

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