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Antimicrobial resistant Salmonella enterica serovar Concord (S. Concord) is known to cause severe gastrointestinal and bloodstream infections in patients from Ethiopia and Ethiopian adoptees, and occasional records exist of S. Concord linked to other countries. The evolution and geographical distribution of S. Concord remained unclear. Here, we provide a genomic overview of the population structure and antimicrobial resistance (AMR) of S. Concord by analysing genomes from 284 historical and contemporary isolates obtained between 1944 and 2022 across the globe. We demonstrate that S. Concord is a polyphyletic serovar distributed among three Salmonella super-lineages. Super-lineage A is composed of eight S. Concord lineages, of which four are associated with multiple countries and low levels of AMR. Other lineages are restricted to Ethiopia and horizontally acquired resistance to most antimicrobials used for treating invasive Salmonella infections in low- and middle-income countries. By reconstructing complete genomes for 10 representative strains, we demonstrate the presence of AMR markers integrated in structurally diverse IncHI2 and IncA/C2 plasmids, and/or the chromosome. Molecular surveillance of pathogens such as S. Concord supports the understanding of AMR and the multi-sector response to the global AMR threat. This study provides a comprehensive baseline data set essential for future molecular surveillance., (© 2023. The Author(s).)

Fluoroquinolone (FQ)-resistant Salmonella spp. were listed by the WHO in 2017 as priority pathogens for which new antibiotics were urgently needed. The overall global burden of Salmonella infections is high, but differs per region. Whereas typhoid fever is most prevalent in South and South-East Asia, non-typhoidal salmonellosis is prevalent across the globe and associated with a mild gastroenteritis. By contrast, invasive non-typhoidal Salmonella cause bloodstream infections associated with high mortality, particularly in sub-Saharan Africa. Most Salmonella strains from clinical sources are resistant to first-line antibiotics, with FQs now being the antibiotic of choice for treatment of invasive Salmonella infections. However, FQ resistance is increasingly being reported in Salmonella, and multiple molecular mechanisms are already described. Whole-genome sequencing (WGS) is becoming more frequently used to analyse bacterial genomes for antibiotic-resistance markers, and to understand the phylogeny of bacteria in relation to their antibiotic-resistance profiles. This mini-review provides an overview of FQ resistance in Salmonella, guided by WGS studies that demonstrate that WGS is a valuable tool for global surveillance.