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

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Abstract
Two clinical isolates of Pseudomonas 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, while P. aeruginosa TL-2 expressed only the naturally occurring bla 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 the bla VEB-1a gene was replaced by a truncated 3′-CS and a 135-bp repeated element (Re). Downstream of the bla VEB-1a gene, an insertion sequence, IS Pa31 disrupted by IS Pa30 , and an orf513 sequence, belonging to a common region (conserved region 1 [CR1]) immediately upstream of the aphA-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 a sul -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-associated bla VEB genes located on a sul -type integron. It also reports for the first time a CR1 element in P. aeruginosa that is associated with an aminoglycoside resistance aphA-6 gene that is expressed from a composite promoter.

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