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JAC Advance Access published online on July 7, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn286
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

Characterization of Salmonella enterica serovar Typhimurium conjugative plasmids transferring resistance to antibiotics and their interaction with the virulence plasmid

H. Hradecka, D. Karasova and I. Rychlik*

Veterinary Research Institute, Hudcova 70, 621 00 Brno, Czech Republic

Received 18 April 2008; returned 12 May 2008; revised 18 June 2008; accepted 18 June 2008

* Corresponding author. Tel: +420-533331201; Fax: +420-541211229; E-mail: rychlik{at}vri.cz

Objectives: 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 ~10% of the transconjugants. Detailed characterization showed that the loss of both resistances was associated with the loss of Tn3 (blaTEM) 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.

Key Words: integrons , Tn3 , Tn1721 , HCM1.225 , rck


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