Incidence and Genomic Background of Antibiotic Resistance in Food-Borne and Clinical Isolates of Serovar Derby from Spain.

serovar Derby (. Derby) ranks fifth among nontyphoidal serovars causing human infections in the European Union. . Derby isolates (36) collected between 2006 and 2018 in a Spanish region (Asturias) from human clinical samples (20) as well as from pig carcasses, pork- or pork and beef-derived products, or wild boar (16) were phenotypically characterized with regard to resistance, and 22 (12 derived from humans and 10 from food-related samples) were also subjected to whole genome sequence analysis. The sequenced isolates belonged to ST40, a common . Derby sequence type, and were positive for SPI-23, a pathogenicity island involved in adherence and invasion of the porcine jejune enterocytes. Isolates were either susceptible (30.6%), or resistant to one or more of the 19 antibiotics tested for (69.4%). Resistances to tetracycline [(A), (B) and (C)], streptomycin (), sulfonamides (), nalidixic acid [ (Asp87 to Asn)] and ampicillin (-like) were detected, with frequencies ranging from 8.3% to 66.7%, and were higher in clinical than in food-borne isolates. The gene was present in all sequenced isolates. The most common phenotype was that conferred by the (A), and genes, located within identical or closely related variants of Genomic Island 1 (SGI1), where mercury resistance genes were also present. Diverse IncI1-I(α) plasmids belonging to distinct STs provided antibiotic [, (A) and/or (B)] and heavy metal resistance genes (copper and silver), while small pSC101-like plasmids carried (C). Regardless of their location, most resistance genes were associated with genetic elements involved in DNA mobility, including a class one integron, multiple insertion sequences and several intact or truncated transposons. By phylogenetic analysis, the isolates were distributed into two distinct clades, both including food-borne and clinical isolates. One of these clades included all SGI1-like positive isolates, which were found in both kinds of samples throughout the entire period of study. Although the frequency of . Derby in Asturias was very low (0.5% and 3.1% of the total clinical and food isolates of recovered along the period of study), it still represents a burden to human health linked to transmission across the food chain. The information generated in the present study can support further epidemiological surveillance aimed to control this zoonotic pathogen.