Mobile Genetic Elements Related to the Diffusion of Plasmid- Mediated AmpC -Lactamases or Carbapenemases from Enterobacteriaceae: Findings from a Multicenter Study in Spain

We examined the genetic context of 74 acquired ampC genes and 17 carbapenemase genes from 85 of 640 Enterobacteriaceae iso-lates collected in 2009. Using S1 pulsed-field gel electrophoresis and Southern hybridization, 37 of 74 blaAmpC genes were located on large plasmids of different sizes belonging to six incompatibility groups. We used sequencing and PCRmapping to investi-gate the regions flanking the acquired ampC genes. The blaCMY-2-like genes were associated with ISEcp1; the surrounding blaDHA genes were similar to Klebsiella pneumoniae plasmid pTN60013 associated with IS26 and the psp and sap operons; and the blaACC-1 genes were associated with IS26 elements inserted into ISEcp1. All of the carbapenemase genes (blaVIM-1, blaIMP-22, and blaIMP-28) were located in class 1 integrons. Therefore, although plasmids are the main cause of the rapid dissemination of ampC genes among Enterobacteriaceae, we need to be aware that other mobile genetic elements, such as insertion sequences, trans-posons, or integrons, can be involved in the mobilization of these genes of chromosomal origin. Additionally, three new inte