Sequencing of plasmids from a multi-antimicrobial resistant Salmonella enterica serovar Dublin strain

Salmonella enterica serovar Dublin (S. Dublin) is a host-adapted serotype whose primary host is cattle, which can serve as a potential reservoir for human infections. S. Dublin remains one of the leading causes of severe invasive infections and deaths associated with salmonellosis. Because of their propensity to cause severe infection, antimicrobial therapy is often required, thus antimicrobial resistance is an important concern. Plasmids play a key role in facilitating drug resistance in these pathogens. This study reports the results of DNA sequencing and sequence analysis of plasmids from a highly multidrug resistant strain (resistant to 11/15 drugs tested) of S. Dublin that originated from cattle. The strain was found to contain four plasmids of approximately 8, 77, 89, and 174 kb. The 174 kb plasmid is an incompatibility group (Inc) A/C plasmid containing genes associated with resistance to at least 9 different antimicrobials, as well as disinfectants and metals. The 88.5 kb plasmid is an IncFIB plasmid containing genes associated with resistance to at least 3 antimicrobial agents and mercurial compounds. The 77 kb plasmid is a S. Dublin virulence plasmid containing multiple virulence-associated genes and the 7.9 kb plasmid encodes mobilization and replication genes. Overall, sequencing identified multiple plasmids containing antimicrobial resistance and virulence genes. The resistance genes identified correlated to the observed resistance phenotype, further indicating the importance of plasmids in antimicrobial resistance in many Salmonella.