Diversity of bla genes and low incidence of CTX-M in plasmid-mediated AmpC-producing Escherichia coli clinical isolates.

The aim of this study was to characterize plasmid-mediated AmpC (pAmpC)-producing Escherichia coli clinical isolates. A total of 101 strains with AmpC-susceptibility pattern were prospectively included. All isolates were tested by multiplex PCR to detect different bla genes. Phylogenetic groups were determined by a multiplex PCR assay. Antimicrobial susceptibility was tested by a microdilution commercial method. Presence of blapAmpC was detected in 79 (78.2%) of the strains; in these pAmpC-producing isolates, blaTEM was detected in 41 (51.9%) strains, blaSHV in 5 (6.3%) strains, blaOXA in 3 (3.8%) strains, and blaCTX-M in 3 (3.8%) strains. blaVIM and blaKPC were detected in one strain. Sixteen strains belonged to phylogroup A, 27 to B1, 20 to B2, and 16 to D. As conclusion, the majority of the strains of E. coli with AmpC-susceptibility pattern are pAmpC positive, although the association of extended-spectrum beta-lactamases (ESBL) and pAmpC is unusual.