Enterobacter cloacae Outbreak and Emergence of Quinolone Resistance Gene in Dutch Hospital

An outbreak of Enterobacter cloacae infections with variable susceptibility to fluoroquinolones occurred in the University Medical Center Utrecht in the Netherlands in 2002. Our investigation showed that a qnrA1 gene was present in 78 (94%) of 83 outbreak isolates and that a qnrA1-encoding plasmid transferred to other strains of the same species and other species. The earliest isolate carrying this same plasmid was isolated in 1999. qnrA1 was located in a complex integron consisting of the intI1, aadB, qacEΔ1, sul1, orf513, qnrA1, ampR, qacEΔ1, and sul1 genes that were not described previously. On the same plasmid, 2 other class 1 integrons were present. One was a new integron associated with the bla(CTX-M-9) extended-spectrum β-lactamase.