e Over a period of 40 months, plasmid-mediated AmpC ␤-lactamases were detected in Tunis, Tunisia, in 78 isolates (0.59%) of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. In 67 isolates, only one ampC gene was detected, i.e., bla CMY-2-type (n ‫؍‬ 33), bla ACC (n ‫؍‬ 23), bla DHA (n ‫؍‬ 6) or bla EBC (n ‫؍‬ 5). Multiple ampC genes were detected in 11 isolates, with the following distribution: bla MOX-2 , bla FOX-3 , and bla CMY-4/16 (n ‫؍‬ 6), bla FOX-3 and bla MOX-2 (n ‫؍‬ 3), and bla CMY-4 and bla MOX-2 (n ‫؍‬ 2). A great variety of plasmids carrying these genes was found, independently of the species and the bla gene. If the genetic context of bla CMY-2-type is variable, that of bla MOX-2 , reported in part previously, is unique and that of bla FOX-3 is unique and new.A mpC ␤-lactamases are cephalosporinases that are poorly inhibited by clavulanic acid (1). AmpC production is one of the mechanisms of resistance to ␤-lactams in enterobacteria, conferring resistance to all ␤-lactams except fourth-generation cephalosporins and carbapenems (2). The genes encoding these enzymes are chromosome or plasmid borne (3).Most plasmid-borne AmpC (pAmpC) ␤-lactamase genes are derived from chromosomal genes that have been mobilized onto plasmids. Based on sequence similarities with species-specific AmpC enzymes, pAmpC variants are classified into five evolutionary groups: the CIT variants (CMY-2 types) originating in Citrobacter freundii, the Enterobacter sp. EBC variants (ACT-1 type, MIR-1), the Morganella morganii DHA variants, the Hafnia alvei ACC variants, and the Aeromonas sp. FOX and MOX variants (1, 2). Several genetic elements are involved in the mobilization of pAmpC ␤-lactamase genes, e.g., the insertion sequences IS26 (CMY-13), ISEcp1 (CMY-2-type, ACC-1-type), and ISCR1, associated with complex integrons (DHA-1 type) (1, 2).The geographic scattering of the different types of pAmpC shows that the CMY-2 type is the most frequent, particularly in Europe (e.g., in France, Spain, Italy,), in Canada, Argentina, and Tunisia (8-10), and in Korea and China (11,12). These pAmpC ␤-lactamases were detected among Enterobacteriaceae, especially in Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Salmonella enterica, and Proteus mirabilis, and also in naturally AmpC-producing species such as Enterobacter cloacae, Enterobacter aerogenes, and C. freundii (13-15).The pAmpC genes have also been reported in animals. Indeed, in the United States, CMY-2-producing E. coli strains have been found among canine clinical isolates (16). Clinical disease associated with AmpC-producing E. coli in dogs in Australia was first reported in 2006 (17). More recently, a survey of clinical isolates of E. coli from dogs and horses in the Netherlands revealed that 2% of them were AmpC producers (8). Furthermore, a Swedish study has described CMY-2-producing E. coli isolated from broilers (18). Such enzymes have been found in Klebsiella isolates from companion animals in Italy (19). In Tunisia, CMY-2-producing E. coli isolate...