Microbiological characterization of plasmid-mediated AmpC ß-lactamases and E. coli hyperproducers: how and why ?

Main Article Content

Annibale Raglio *
Marco Arosio
Paola Stano
Angela Acerbis
Francesca Vailati
Marco Passera
Annalisa Grigis
Antonio Goglio
(*) Corresponding Author:
Annibale Raglio | araglio@ospedaliriuniti.bergamo.it


The aim of this study is the evaluation of phenotypic method for the detection of plasmid-mediated AmpC producing Enterobacteriaceae by agar diffusion.We developed a phenotypic method with double disk test (CLSI) and evaluation of synergism between Cloxacillin and/or Boronic Acid with cefotaxime and ceftazidime and cefepime with amoxicillin/clavulanic acid. As reference method for AmpC detection we used a multiplex PCR according to Perez-Perez. Among 7476 Enterobacteriaceae we detected 45 strains: 37 (82.2%) plasmid-mediated AmpC producers, 6 (13.3%) E. coli hyperproducers and 2 E. coli (4.5%) positive for both.The AmpC phenotypic test was positive for all the isolates, showing a typical ghost zone between cloxacillin and cephalosporins or boronic acid and cephalosporins.The AmpC multiplex PCR confirmed that 28 P. mirabilis and 7 E. coli harboured a gene belonging to the bla-CMY-LAT family. Sequencing defined the presence of CMY-16 in all P. mirabilis, CMY-2 in E. coli, DHA-1 in 3 K. pneumoniae and FOX in 1 K. pneumoniae and allowed us to identify eight strains as E. coli hyperproducer: six E. coli yielded no amplicon and 2 were also producer of CMY-2. In this study the phenotypic method showed a sensitivity and a specificity of 100%.Waiting for the indication of international authorities, we think this phenotypic screening method could be useful in the routine of microbiological laboratories.

Downloads month by month


Download data is not yet available.

Article Details

Most read articles by the same author(s)

1 2 > >>