Clin Microbiol Infect 2010; 16: 171–178
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 β-lactamases (PABLs). Antimicrobial susceptibility testing was performed for β-lactam and non-β-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 blaAmpC sequencing, characterization of the blaAmpC 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 blaCMY-2 (n = 35), blaCMY-7 (n = 1) and blaDHA-1 (n = 2), from out- (n = 23) and in-patients (n = 15), moderate-high MICs of β-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 blaCMY-2 and blaCMY-7 were linked to ISEcp1 upstream in 32 cases and in one case, respectively, and blaDHA-1 was linked to qacEΔ1sul1 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; blaCMY-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 blaCMY-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.