Complex Genetic Structures with Repeated Elements, a sul -Type Class 1 Integron, and the bla VEB Extended-Spectrum β-Lactamase Gene

Two clinical isolates ofPseudomonas aeruginosa , TL-1 and TL-2, were isolated from a patient transferred from Bangladesh and hospitalized for osteomyelitis in Paris, France.P. aeruginosa TL-1 expressed the extended-spectrum β-lactamase VEB-1a and was susceptible only to imipenem and colistin, whileP. aeruginosa TL-2 expressed only the naturally occurringbla AmpC gene at a basal level and exhibited a wild-type β-lactam resistance phenotype. In TL-1, the typical 5′-end conserved sequence (5′-CS) region of class 1 integrons usually present upstream of thebla VEB-1a gene was replaced by a truncated 3′-CS and a 135-bp repeated element (Re). Downstream of thebla VEB-1a gene, an insertion sequence, ISPa31 disrupted by ISPa30 , and anorf513 sequence, belonging to a common region (conserved region 1 [CR1]) immediately upstream of theaphA-6 gene, were present. Further downstream, a second truncated 3′-CS region in direct repeat belonged to In51, an integron containing two gene cassettes (aadA6 and the OrfD cassette). Thus, the overall structure corresponded to asul -type class 1 integron termed In121. Genetic analyses revealed that both isolates were clonally related and differed by a ca. 100-kb fragment that contained In121. Both isolates contained another integron, In122, that carried three gene cassettes:aadB ,dfrA1 , and the OrfX cassette. This work identifies for the first time the spread of Re-associatedbla VEB genes located on asul -type integron. It also reports for the first time a CR1 element inP. aeruginosa that is associated with an aminoglycoside resistanceaphA-6 gene that is expressed from a composite promoter.