Characterization of a Self-Transferable Plasmid from Salmonella enterica Serotype Typhimurium Clinical Isolates Carrying Two Integron-Borne Gene Cassettes Together with Virulence and Drug Resistance Genes

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Abstract
An unusual self-transferable virulence-resistance plasmid (pUO- St VR2) was found in nine multidrug-resistant (ACSSuT phenotype) Salmonella enterica serotype Typhimurium clinical isolates that were assigned to four different phage types and a single and distinctive Xba I pulsed-field gel electrophoresis profile. pUO- St VR2 is an IncFII plasmid of about 140 kb in length carrying the spvA , spvB , and spvC ( Salmonella plasmid virulence) and rck (resistance to complement killing) genes. It also carries the oxa1/aadA1a (ampicillin resistance and streptomycin-spectinomycin resistance) gene cassette configuration located within a class 1 integron with qacEΔ1/sul1 (ammonium antiseptics resistance and sulfadiazine resistance); the transposon genes merA , tnpA , and tnpR (mercury resistance, transposase, and resolvase of Tn 21 , respectively); and the catA1 (chloramphenicol resistance) and tet (B) (tetracycline resistance) genes. The insertion of resistance genes into a Salmonella virulence plasmid constitutes a new and interesting example of plasmid evolution and presents a serious public health problem.