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

ABSTRACTAn unusual self-transferable virulence-resistance plasmid (pUO-StVR2) was found in nine multidrug-resistant (ACSSuT phenotype) Salmonella entericaserotype Typhimurium clinical isolates that were assigned to four different phage types and a single and distinctive XbaI pulsed-field gel electrophoresis profile. pUO-StVR2 is an IncFII plasmid of about 140 kb in length carrying the spvA, spvB, and spvC(Salmonellaplasmid 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 Tn21, respectively); and the catA1(chloramphenicol resistance) and tet(B) (tetracycline resistance) genes. The insertion of resistance genes into a Salmonellavirulence plasmid constitutes a new and interesting example of plasmid evolution and presents a serious public health problem.