Plasmid-mediated AmpC b-lactamases in Enterobacteriaceae lacking a chromosomal ampC gene and E. coli: prevalence at a Swiss university hospital and distribution of the different molecular types in the northern part of Switzerland

Abstract number: 1733_525

Adler H., Fenner L., Hohler D., Frei R.

Objectives: (1) to determine the prevalence of plasmid-mediated AmpC b-lactamases in isolates of Enterobacteriaceae lacking a chromosomal ampC gene and E. coli at the University Hospital Basel. (2) to determine which types of plasmid-mediated AmpC b-lactamases occur in the northern part of Switzerland.

Methods: Between January 27 and September 27, 2006, a total of 2,100 consecutive clinical isolates of E. coli and Enterobacteriaceae naturally lacking a chromosomal ampC gene were screened for resistance to cefoxitin with the disk diffusion test. Furthermore, clinical isolates suspected to harbour a plasmid-mediated AmpC b-lactamase were collected from laboratories in the northern part of Switzerland. Multiplex AmpC PCR (Perez-Perez and Hanson, 2002, J Clin Microbiol 40: 2153–62) was performed on all cefoxitin-resistant isolates. The ampC genes of the PCR-positive isolates were sequenced.

Results: (1) One hundred of the consecutive clinical isolates were cefoxitin-resistant. Plasmid mediated AmpC b-lactamases were found in three isolates of E. coli. Thus, the prevalence of plasmid-mediated AmpC b-lactamases was 0.14%. (2) Plasmid-mediated AmpC b-lactamases were found in 16 isolates from 5 laboratories in the northerm part of Switzerland. Thirteen of the isolates were E. coli, 2 were Klebsiella pneumoniae and one was Proteus mirabilis. CMY-2 and CMY-2 like AmpC b-lactamases were detected in 11 isolates of E. coli, 2 isolates of K. pneumoniae and one isolate of P. mirabilis. DHA-1 was detected in 2 isolates of E. coli.

Conclusion: (1) The prevalence of 0.14% of plasmid-mediated AmpC b-lactamases in Enterobacteriaceae lacking a chromosomal ampC-gene plus E. coli at the University Hospital Basel is very low. (2) CMY-2 and CMY-2 like AmpC b-lactamases are the predominant plasmid-mediated AmpC b-lactamases (87.5%) in the northern part of Switzerland. DHA-1 was the only other AmpC b-lactamase that was found (12.5%).