The role of IS26 in evolution of a derivative of the virulence plasmid of Salmonella enterica serovar Enteritidis which confers multiple drug resistance.

Abstract pUO-SeVR1 is a resistance derivative of pSEV, the virulence plasmid specific of Salmonella enterica serovar Enteritidis. It was first detected in a Spanish isolate involved in gastroenteritis, but closely related plasmids are widespread in highly invasive isolates originating from Africa. According to its nucleotide sequence, pUO-SeVR1 consists of 110,982 bp with a GC content of 53.2%. It confers resistance to multiple antimicrobial agents and contains a wealth of mobile genetic elements, including 14 copies of IS 26 which have played a major role in the evolution of the plasmid. An intact copy of IS 4321 and remnants of many other transposable elements (Tn 2 , Tn 21 , Tn 1721 and Tn 5393 ) are also detected. Most of the pSEV sequence is conserved in pUO-SeVR1 but small deletions, major inversions and the insertion of two foreign regions (of 38.7 and 13.6 kb, where the resistance genes are clustered), have occurred. Plasmids of the IncL/M, IncN and IncQ groups could have contributed to the assembly of the resistance regions.