Session: Poster Session: Pseudomonas aeruginosa
Sunday, October 26, 2008: 12:00 AM
Room: Hall C
Background: The GES-type ESBLs constitute an important mechanism that mediates ceftazidime (CAZ) resistance and has recently emerged in Pae from Argentina. Up to now, blaGES genes were only found as cassettes of sulI-containing class 1 integrons (sulI-In) in several parts of the world. Methods: 65 out of 17,645 Pseudomonas spp. isolates from WHONET-Argentina clinical laboratories (2001 to 2005) showed an ESBL-phenotype (unusual CAZ/imipenem synergism) and were confirmed as GES producers by PCR. A representative subset of these isolates (20 Pae, 1 P. putida) from 11 hospitals was studied. MICs were determined by agar dilution (CLSI). Integron cartography was done by PCR using primers against the 5'- and 3’-conserved sequence (3’CS, sulI-In) or the tniC gene of the Tn402 transposition module, combined with blaGES primers. DNA sequencing was done by standard methods. Results: CAZ MICs were 32-256 µg/ml for all but one isolate (8 µg/ml). Integron cartography resulted in 15 Pae and 1 P. putida with sulI-In that harbor blaGES-1 as (n): a unique cassette (1); the first of 2, 3 or 4 cassettes (11, 1 and 2, respectively), or the second of 2 cassettes (1). Interestingly, in the remaining 5 isolates blaGES-1 was found in class 1 integrons that lack the 3’CS but have the tniC of Tn402, with the following cassette arrays (n): blaGES-1 / aac(6’)-Ib (3, from different regions of Argentina); aac(6’)-Ib / aacA7 / blaGES-1 (1), and aacA7 / blaGES-1 / aac(6’)-Ib / cassette 4 (unknown function) / blaOXA-2 (1). The cassette 4 was 94% identical to that of a sulI-In harbored in plasmid pSp33 from a wastewater uncultured bacterium. Conclusions: This is the first report on an ESBL gene linked to tniC of Tn402. The transposition potential of this genetic platform, found in 5/21 of GES producing Pseudomonas isolates, may have great impact on the epidemiology of such important resistant mechanism.