Genomic characterization of multidrug- resistant Salmonella serovar Kentucky ST198 isolated in poultry flocks in Spain (2011-2017)

Salmonella Kentucky is commonly found in poultry and rarely associated with human disease. However, a multidrug- resistant (MDR) S. Kentucky clone [sequence type (ST)198] has been increasingly reported globally in humans and animals. Our aim here was to assess if the recently reported increase of S. Kentucky in poultry in Spain was associated with the ST198 clone and to characterize this MDR clone and its distribution in Spain. Sixty- six isolates retrieved from turkey, laying hen and broiler in 2011-2017 were subjected to whole- genome sequencing to assess their sequence type, genetic relatedness, and presence of antimicrobial resistance genes (ARGs), plasmid replicons and virulence factors. Thirteen strains were further analysed using long- read sequencing technologies to characterize the genetic background associated with ARGs. All isolates belonged to the ST198 clone and were grouped in three clades associated with the presence of a specific point mutation in the gyrA gene, their geographical origin and isolation year. All strains carried between one and 16 ARGs whose presence correlated with the resistance phenotype to between two and eight antimicrobials. The ARGs were located in the Salmonella genomic island (SGI- 1) and in some cases (blaSHV-12, catA1, cmlA1, dfrA and multiple aminoglycoside- resistance genes) in IncHI2/IncI1 plasmids, some of which were consistently detected in different years/farms in certain regions, suggesting they could persist over time. Our results indicate that the MDR S. Kentucky ST198 is present in all investigated poultry hosts in Spain, and that certain strains also carry additional plasmid- mediated ARGs, thus increasing its potential public health significance.

Automated summary

This study assessed whether the increase of Salmonella Kentucky in poultry in Spain was associated with the multidrug-resistant ST198 clone. The results showed that the ST198 clone was present in all investigated poultry hosts in Spain and certain strains carried additional plasmid-mediated antimicrobial resistance genes, increasing its potential public health significance.