Diversity of Plasmids Encoding Virulence and Resistance Functions in <i>Salmonella enterica</i> subsp. <i>enterica</i> Serovar Typhimurium Monophasic Variant 4,[5],12:i:- Strains Circulating in Europe

<div><p>Plasmids encoding resistance and virulence properties in multidrug resistant (MDR) <i>Salmonella enterica</i> (<i>S</i>.) serovar Typhimurium monophasic variant 4,[5],12:i:- isolates recovered from pigs and humans (2006-2008) in Europe were characterised. The isolates were selected based on the detection by PCR-amplification of <i>S</i>. Typhimurium virulence plasmid pSLT genes and were analysed by multi-locus sequence typing (MLST). The resistance genes present in the isolates and the association of these genes with integrons, transposons and insertion sequences were characterised by PCR-sequencing, and their plasmid location was determined by alkaline lysis and by S1-nuclease pulsed-field gel electrophoresis (PFGE) Southern-blot hybridisation. Plasmids were further analysed by replicon typing, plasmid MLST and conjugation experiments. The 10 <i>S</i>. 4,[5],12,i:- selected isolates belonged to ST19. Each isolate carried a large plasmid in which MDR with pSLT-associated virulence genes were located. After analysis, eight different plasmids of three incompatibility groups (IncA/C, IncR and IncF) were detected. Two IncA/C plasmids represented novel variants within the plasmid family of the <i>S</i>. 4,[5],12:i:- Spanish clone, and carried an empty class 1 integron with a conventional <i>qacE</i>Δ<i>1</i>-<i>sul1</i> 3′ conserved segment or an In-<i>sul3</i> type III with <i>estX-psp-aadA2-cmlA1-aadA1-qacH</i> variable region linked to <i>tnpA440-sul3</i>, part of Tn<i>2</i>, Tn<i>21</i> and Tn<i>1721</i> transposons, and IS<i>CR2</i>. Four newly described IncR plasmids contained the resistance genes within In-<i>sul3</i> type I (<i>dfrA12-orfF-aadA2-cmlA1-aadA1-qacH</i>/<i>tnpA440</i>-<i>sul3</i>) and part of Tn<i>10</i> [<i>tet</i>(B)]. Two pSLT-derivatives with FIIs-ST1+FIB-ST17 replicons carried <i>cmlA1</i>-[<i>aadA1-aadA2</i>]-<i>sul3-dfrA12</i> and <i>bla</i>_TEM-1 genes linked to an In-<i>sul3</i> type I integron and to Tn<i>2</i>, respectively. In conclusion, three emerging European clones of <i>S</i>. 4,[5],12:i:- harboured MDR plasmids encoding additional virulence functions that could contribute significantly to their evolutionary success.</p>