Clinical isolates of Escherichia coli with reduced susceptibility to oxyimino-cephalosporins and not susceptible to clavulanic acid synergy (n = 402), collected from Norwegian diagnostic laboratories in 2003-2007, were examined for the presence of plasmid-mediated AmpC beta-lactamases (PABLs). Antimicrobial susceptibility testing was performed for beta-lactam and non-beta-lactam antibiotics using Etest and Vitek2, respectively. The AmpC phenotype was confirmed using the boronic acid test. PABL-producing isolates were detected using ampC multiplex-PCR and examined by bla(AmpC) sequencing, characterization of the bla(AmpC) genetic environment, phylogenetic grouping, XbaI- pulsed-field gel electrophoresis (PFGE), multi-locus sequence typed (MLST), plasmid profiling and PCR-based replicon typing. For the PABL-positive isolates (n = 38), carrying bla(CMY-2) (n = 35), bla(CMY-7) (n = 1) and bla(DHA-1) (n = 2), from out- (n = 23) and in-patients (n = 15), moderate-high MICs of beta-lactams, except cefepime and carbapenems, were determined. All isolates were resistant to trimethoprim-sulphamethoxazole. Multidrug resistance was detected in 58% of the isolates. The genes bla(CMY-2) and bla(CMY-7) were linked to ISEcp1 upstream in 32 cases and in one case, respectively, and bla(DHA-1) was linked to qacEDelta1sul1 upstream and downstream in one case. Twenty isolates were of phylogenetic groups B2 or D. Thirty-three XbaI-PFGE types, including three clusters, were observed. Twenty-five sequence types (ST) were identified, of which ST complexes (STC) 38 (n = 7), STC 448 (n = 5) and ST131 (n = 4) were dominant. Plasmid profiling revealed 1-4 plasmids (50-250 kb) per isolate and 11 different replicons in 37/38 isolates; bla(CMY-2) was carried on transferable multiple-replicon plasmids, predominantly of Inc groups I1 (n = 12), FII (n = 10) and A/C (n = 7). Chromosomal integration was observed for bla(CMY-2) in ten strains. CMY-2 is the dominant PABL type in Norway and is associated with ISEcp1 and transferable, multiple-replicon IncI1, IncA/C, or IncFII plasmids in nationwide strains of STC 448, STC 38 and ST131.
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