Transferable Quinolone Resistance (TQR) in Enterobacteria from Argentina: aac(6’)-Ib-cr and a Novel qnr Allele (qnrB6) Are Located in a Complex Class 1 Integron

PETRONI A; ANDRES P; QUIROGA MP; SOLER-BISTUÉ A; ZORREGUIETA A; CENTRÓN D; GALAS M

USA

Congreso; 47th Interscience Conference on Antimicrobial Agents and Chemotherapy; 2007

American Society for Microbiology

Background: The worldwide emergence of TQR is becoming one of the major threats in bacterial resistance. In Argentina, TQR was not reported yet. Methods: The clinical multiresistant (MR) Klebsiella pneumoniae (Kpn) M7943 was from Buenos Aires (2006). Escherichia coli J53 azide-resistant (AzR) was the recipient strain in conjugative assays. MICs were determined by the agar dilution method (CLSI). Conjugations, PCR and DNA sequencing were performed by standard methods. Long PCR assays were done with Elongase (Invitrogen). Results: An ISCR1-containing class 1 integron, named InK122 (approx. 15 kb), was found in Kpn M7943 and was transferred by conjugation to E. coli J53 AzR, rendering transconjugant M7943-Tc. Relevant susceptibility profiles of Kpn M7943 and E. coli M7943-Tc were, respectively (MIC, µg/ml): nalidixic acid, 128/16; ciprofloxacin, 32/2; levofloxacin, 4/0.5; amikacin, 16/4; tobramycin, 16/16. InK122 showed a 4-cassettes variable region: aac(6’)-Ib-cr, blaOXA-30, catB3 and arr-3. This region was 96% identical to that of In37 (differences were mainly at the 5’ ends of the aac(6’)-Ib-cr genes). InK122 harbored the novel qnrB6 allele, in a 5401-bp region located between ISCR1 and a second copy of the 3’conserved sequence. This region contained a sap-like operon (sapC, B and A), qnrB6 and a portion of the psp operon (pspF), placed antisense to ISCR1. The deduced QnrB6 protein (226 amino acids) had 98% identity with QnrB5. The same qnrB6-containing region was found in 7 independent MR clinical isolates from Buenos Aires (2005), 2 Citrobacter freundii and 5 Enterobacter spp. Conclusion: Both aac(6’)-Ib-cr and qnr-mediated TQR were identified in Argentina.  A national surveillance is essential to estimate the prevalence of these mechanisms.