Characterization of Salmonella enterica serovar Typhimurium conjugative plasmids transferring resistance to antibiotics and their interaction with the virulence plasmid.
OBJECTIVE
In this study, we analysed field isolates of Salmonella enterica serovar Typhimurium for the presence of conjugative plasmids transferring resistances to antibiotics.


METHODS
Altogether 23 strains were analysed for the presence of conjugative R-plasmids. In the case of successful conjugation, the R-plasmids were characterized by PCR for antibiotic resistance genes, integrons and replicon typing. Variable regions of integrons were sequenced.


RESULTS
Conjugation and transfer of antibiotic resistance was observed in 12 strains. Conjugative plasmids in these strains belonged to the IncI1 and IncHI1 replicons and four of them transferred antibiotic resistance associated with class I integrons. In two cases, resistance to tetracycline and/or ampicillin was not transferred by conjugation to approximately 10% of the transconjugants. Detailed characterization showed that the loss of both resistances was associated with the loss of Tn3 (bla(TEM)) and Tn1721 [tet(A)] from the conjugative plasmids p9046 and p9134. However, when only the tetracycline resistance was lost, the Tn1721 was replaced with a partial sequence of rck, and with complete coding sequences of srgA, srgB, ORF7 and pefI originating from the Salmonella Typhimurium virulence plasmid.


CONCLUSIONS
Two plasmids from our collection were capable of recombination with the virulence plasmid of Salmonella Typhimurium and subsequently spread both antibiotic resistance and virulence genes to the recipient.
Hradecka
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Veterinary Research Institute, Hudcova 70, 621 00 Brno, Czech Republic.
Karasova
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D
Rychlik
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D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D023061:Gene Order; D015321:Gene Rearrangement; D005838:Genotype; D006801:Humans; D032023:Integrons; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D012093:Replicon; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D026801:Synteny; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D037521:Virulence Factors