Vibrio cholerae multiple resistance is encoded by a transposonlike structure including a class 1 integron that harbors aac(6´)I-b and blaCTX-M-2.

A SOLER BISTUÉ, F MARTIN, D FACCONE, A PETRONI, M GALAS, A ZORREGUIETA, M E TOLMASKY

Washington

Congreso; 45th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC); 2005

American Society for Microbiology

Background: There have been seven cholera outbreaks since 1992 in Argentina. An analysis of 1947 isolates showed that 26 of them were resistant to extended spectrum cephalosporins and amikacin. We analyzed one of them and showed that the resistance determinants were present in a conjugative plasmid (pAS1). Methods: DNA sequencing was performed using as templates amplicons obtained by PCR of relevant regions of the V. cholerae plasmid pAS1. AAC(6?)-Ib was overexpressed by cloning using the pT7-5 vector and detected by Western blotting using anti-AAC(6?)-Ib serum. Results: Sequencing of a pAS1 14.7-kb fragment led to identification of a structure resembling a transposition element related to Tn1696 with a copy of IS4321 inserted inside the IR at the 5? end.  The tnpA, tnpR and res loci are identical to those in Tn1696. A class 1 integron closely related to InS21 and In116 is located 3? of the res site which includes: a) a copy of an aac(6?)-Ib variant potentially coding for a protein including a 20-amino acid repeat at the N-terminus and that has been shown to be larger than that coded for by Tn1331 by immunoblot, b) a copy of blaOXA-2 that, unlike in InS21, potentially codes for a functional OXA-2, and 3) a copy of blaCTX-M-2. Conclusion: The V. cholerae pAS1 plasmid, which is conjugative and can replicate in E. coli, includes a potential mobile element including the clinically relevant aac(6?)-Ib and blaCTX-M2 genes. Although aminogylcosides are not used in the treatment of V. cholerae, this bacterium can act as a reservoir of resistance genes and participate in the dissemination of resistance to amikacin and extended-spectrum b-lactamases at the molecular as well as at the cellular level.