Conjugative IncFI plasmids carrying CTX-M-15 among Escherichia coli ESBL producing isolates at a University hospital in Germany

Abstract

Background: Multi-drug-resistant, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, constitute an emerging public-health concern. Little data on the molecular epidemiology of ESBL producing Escherichia coli is available in Germany. Here we describe the prevalence and molecular epidemiology of ESBL producing-Escherichia coli isolates at a German University hospital.

Methods: We analysed 63 non-duplicate clinical ESBL isolates obtained over an 8-month period using PCR and sequence-based ESBL allele typing, plasmid replicon typing, phylogenetic group typing. Pulsed-field gel electrophoresis (PFGE) based genotyping and plasmid profiling was performed, as well as confirmatory DNA-based hybridization assays.

Results: Examination of the 63 Escherichia coli isolates revealed an almost equal distribution among the E. coli phylogenetic groups A, B1, B2 and D. High prevalence (36/63) of the CTX-M-15 gene was observed and an analysis of PFGE-based patterns revealed the presence of this CTX-M allele in multiple clones. Resistance to cefotaxime was a transferable trait and a commonly occurring 145.5 kb conjugative IncFI plasmid was detected in 65% of E. coli carrying the CTX-M-15 allele. The rate of transferable antibiotic resistances for GM, SXT, TET, GM-SXT-TET, SXT-TET and GM-TET was 33%, 61%, 61%, 27%, 44% and 11%, respectively. The remaining strains did not have a common IncFI plasmid but harboured transferable IncFI plasmids with sizes that ranged from 97 to 242.5 kb.

Conclusion: Our data demonstrate the presence of IncFI plasmids within the prevailing E. coli population in a hospital setting and suggest that the dissemination of CTX-M-15 allele is associated to lateral transfer of these well-adapted, conjugative IncFI plasmids among various E. coli genotypes.

Figure 1

PFGE dendogram of ESBL-producing E. coli. Heterogeneity of the 63 E. coli ESBL producers are seen on the dendograms. The diagram also shows the isolate number, PFGE types as well as the corresponding phylogenetic group. The dashed line X indicates SAB of 0.8 revealing six clusters 1–6; PFGE types are labelled X1–X13.

Figure 2

Agarose gel showing S1 nuclease PFGE-based sizing of large plasmids for 8 isolates. M (Lambda Marker) indicates the molecular weight marker of concatenated multimers of the bacteriophage lambda genome. Plasmid preparations from isolate number 48, 67, 79, 90, 58, 70, 110 and 112 reveal plasmids with sizes ranging from 45.5 kb to 194 kb which are indicated with arrows.