Abstract: Objectives: To gain insights into ampC transmission between bacterial strains. Methods: We examined the genetic context of 117 acquired ampC genes from 27119 Enterobacteriaceae collected between 1999 and 2007. Plasmid analysis was carried out by PCR-based replicon or relaxase typing, S1-PFGE and Southern hybridization. I-CeuI/PFGE was used for isolates not characterized by plasmid analysis. PCR reactions were used to map the genetic organization of the ampC genes. Results: Among the isolates studied, 81.2% of ampC genes were located on plasmids of known Inc/MOB groups, 7.7% were chromosomally located and 11.1% were not determined. A/C, I1 and K were the most commonly found replicons in plasmids carrying blaCMY-2, while L/M replicons were associated with blaDHA-1. blaACC-1 was linked to I1 and MOBF11 plasmids; blaCMY-27 was associated with IncF and MOBP12 plasmids; the plasmid carrying blaCMY-25 could not be typed, and blaCMY-40 was chromosomally located. All 87 isolates carrying blaCMY-2, blaCMY-4, blaCMY-25, blaCMY-27, blaCMY-40 or blaACC-1 displayed the transposon-like structures ISEcp1/?ISEcp1-blaCMY-blc-sugE or ?ISEcp1-blaACC-1-gdha. The most prevalent structure in blaDHA-1 (93.3% of cases) was identical to that described in the Klebsiella pneumoniae pTN60013 plasmid. Remarkably, in three isolates containing chromosomal blaCMY-2, this gene was mobilized by conjugation. Conclusions: Although plasmids are the main cause of the rapid dissemination of ampC genes among bacteria, we need to be aware that other mobile genetic elements such as integrative and conjugative elements (ICEs) can be involved in the mobilization of these genes.

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