| Summary: | Poultry products are still an important cause of <i>Salmonella</i> infections worldwide, with an increasingly reported expansion of less-frequent serotypes or atypical strains that are frequently multidrug-resistant. Nevertheless, the ability of <i>Salmonella</i> to survive antimicrobials promoted in the context of antibiotic reducing/replacing and farming rethinking (e.g., organic acids and copper in feed/biocides) has been scarcely explored. We investigated <i>Salmonella</i> occurrence (conventional and molecular assays) among chicken meat at the processing stage (<i>n</i> = 53 batches/29 farms) and characterized their tolerance to diverse stress factors (antibiotics, copper, acid pH, and peracetic acid). Whole-genome sequencing was used to assess adaptive features and to perform comparative analysis. We found a low <i>Salmonella</i> occurrence (4%) and identified <i>S</i>. Enteritidis/ST11 plus atypical non-H<sub>2</sub>S-producing <i>S</i>. 1,4,[5],12:i:-/ST3478. The ST3478 presented the ability to grow under diverse stresses (antibiotics, copper, and acid-pH). Comparative genomics among ST3478 isolates showed similar antibiotic/metal resistance gene repertoires and identical nonsense <i>phsA</i> thiosulfate reductase mutations (related to H<sub>2</sub>S-negative phenotype), besides their close phylogenetic relationship by cgMLST and SNPs. This study alerts for the ongoing national and international spread of an emerging monophasic <i>Salmonella</i> Typhimurium clonal lineage with an enlarged ability to survive to antimicrobials/biocides commonly used in poultry production, being unnoticed by conventional <i>Salmonella</i> detection approaches due to an atypical non-H<sub>2</sub>S-producing phenotype.
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