CARB-9, a new B-lactamase Encoded within the Super-Integron (SI) of Vibrio cholerae (Vch).

MELANO R; PETRONI A; SAKA H; GARUTTI A; MANGE L; PASTERAN F; RAPOPORT M; MIRANDA M; FACCONE D; ROSSI A; HOFFMAN P; GALAS M

Chicago, USA

Congreso; 43rd Interscience Conference of Antimicrobial Agents and Chemotherapy; 2003

Background: Recently, we reported a new â-lactamase gene, blaCARB-7, located in the SI of Vch. In addition to CARB-7 (pI 5.4), another â-lactamase with pI 5.2, was detected (40% of prevalence) in the same sample of Vch non-O1, non-O139, Argentinean isolates. One strain (BA5) of this last group was studied. Methods: MICs were determined by agar dilution method according to NCCLS specifications, adopting the Enterobacteriaciae criteria for â-lactams oher than ampicillin (AMP). Conjugative assays, DNA cloning and sequencing were performed by standard methods. Phylogenetic analysis was implemented with the Clustal X software. Results: BA5 showed the following susceptibility profile (MIC, ìg/ml): AMP, 64; AMP-sulbactam, 4; ticarcilin (TIC), 128; TIC-clavulanate, 1; cephalotin, 0.25, and piperacillin, 8. These MICs were 4 to 8 times lower than those conferred by CARB-7. Nucleotide sequence analysis of 4 Kb-HindIII fragment from BA5 showed an ORF which was phylogenetically related to genes encoding CARB-enzymes. The deduced protein [288 amino acid (aa), named CARB-9, shared 99% identity with CARB-7 (three aa of difference), 89 % with CARB-6 and an overall 84% with other CARB-enzymes. The blaCARB-9 gene could not be transferred to E. coli by conjugation. Five 123-bp and one 122-bp Vch pepeats (VCR) were detected in the sequences flanking blaCARB-9. The sequence downstream to blaCARB-9 shared 99% identity with the TIGR locus VCA0455 located in the Vch chromosome 2. Both upstream and downstream sequences of blaCARB-7. Conclusions: The new blaCARB-9 gene is located inside of VCR region, in a different location respective of blaCARB-7. This work constitutes a new evidence that the Vch SI may act as a system of in vivo gene capture, as well as a reservoir of resistance genes.