Alessia Bertini

Multilocus sequence typing of IncI1 plasmids carrying extended-spectrum β-lactamases in Escherichia coli and Salmonella of human and animal origin

OBJECTIVES Plasmids belonging to incompatibility group I1 (IncI1) are widespread in Enterobacteriaceae and are characterized by the presence of a cluster of genes encoding the type IV pili, contributing to the virulence of Shiga-toxigenic Escherichia coli. Recently, IncI1 plasmids were identified in E. coli and Salmonella strains of animal origin as responsible for the dissemination of beta-lactamase genes. Plasmid multilocus sequence typing (pMLST) was developed to discern naturally occurring IncI1 plasmids in homogeneous groups according to their allele assortment. METHODS pMLST was developed by selecting multiple target genes on the available complete IncI1 plasmid DNA sequences. Sixteen plasmids, all assigned to the IncI1 group by the PCR-based replicon typing method, were included in this study. They were analysed for beta-lactamase genes and typed by restriction fragment length polymorphism (RFLP) and pMLST. RESULTS Sixteen plasmids identified in E. coli and Salmonella isolated from animals and humans in different countries carried bla(CMY-2), bla(CTX-M-15), bla(CTX-M-1), bla(CTX-M-14), bla(TEM-52), bla(SHV-12) or bla(TEM-1) beta-lactamase genes. These plasmids were classified by RFLP in nine different groups corresponding to the nine sequence types determined by pMLST. CONCLUSIONS The pMLST method was suitable for rapid and easy subtyping of IncI1 plasmids. This study demonstrates that the pMLST method can contribute to the epidemiological description of circulation of specific resistance plasmids among beta-lactamase producers isolated from animals and humans.

Replicon Typing of Plasmids Encoding Resistance to Newer β-Lactams

Polymerase chain reaction–based replicon typing represents a novel method to describe the dissemination and follow the evolution of resistance plasmids. We used this approach to study 26 epidemiologically unrelated Enterobacteriaceae and demonstrate the dominance of incompatibility (Inc) A/C or Inc N-related plasmids carrying some emerging resistance determinants to extended-spectrum cephalosporins and carbapenems.

Extended-Spectrum β-Lactamase CTX-M-1 in Escherichia coli Isolates from Healthy Poultry in France

ABSTRACT Genes encoding extended-spectrum β-lactamase CTX-M-1 were detected in 12 Escherichia coli isolates recovered over a 7-month period from the ceca of healthy poultry in seven districts in France in 2005. Eleven of those strains were not clonally related and had a blaCTX-M-1 gene located on transferable plasmids of different sizes and structures.

Characterization and PCR-Based Replicon Typing of Resistance Plasmids in Acinetobacter baumannii

ABSTRACT Acinetobacter baumannii is an opportunistic pathogen, especially in intensive care units, and multidrug-resistant isolates have increasingly been reported during the last decade. Despite recent progress in knowledge of antibiotic resistance mechanisms in A. baumannii, little is known about the genetic factors driving isolates toward multidrug resistance. In the present study, the A. baumannii plasmids were investigated through the analysis and classification of plasmid replication systems and the identification of A. baumannii-specific mobilization and addiction systems. Twenty-two replicons were identified by in silico analysis, and five other replicons were identified and cloned from previously uncharacterized A. baumannii resistance plasmids carrying the OXA-58 carbapenem-hydrolyzing oxacillinase. Replicons were classified into homology groups on the basis of their nucleotide homology. A novel PCR-based replicon typing scheme (the A. baumannii PCR-based replicon typing [AB-PBRT] method) was devised to categorize the A. baumannii plasmids into homogeneous groups on the basis of the nucleotide homology of their respective replicase genes. The AB-PBRT technique was applied to a collection of multidrug-resistant A. baumannii clinical isolates carrying the blaOXA-58 or blaOXA-23 carbapenemase gene. A putative complete conjugative apparatus was identified on one plasmid whose self-conjugative ability was demonstrated in vitro. We showed that this conjugative plasmid type was widely diffused in our collection, likely representing the most important vehicle promoting the horizontal transmission of A. baumannii resistance plasmids.

Dissemination of an Extended-Spectrum-β-Lactamase blaTEM-52 Gene-Carrying IncI1 Plasmid in Various Salmonella enterica Serovars Isolated from Poultry and Humans in Belgium and France between 2001 and 2005

ABSTRACT We report here the dissemination of a conjugative IncI1 plasmid carrying blaTEM-52 on a Tn3 transposon conferring resistance to extended-spectrum cephalosporins in Salmonella enterica serovar Agona, Derby, Infantis, Paratyphi B dT+, and Typhimurium isolates from poultry and humans in Belgium and France from 2001 to 2005. The most prevalent serovar spreading this resistance was serovar Infantis.

Multicopy blaOXA-58 Gene as a Source of High-Level Resistance to Carbapenems in Acinetobacter baumannii

ABSTRACT The mechanisms at the origin of heterogeneous carbapenem resistance levels observed among Acinetobacter baumannii isolates collected in 2005 in a large University Hospital of Rome, Italy, were investigated. These isolates were related and possessed similar plasmids carrying the carbapenem-hydrolyzing oxacillinase gene blaOXA-58 but showed variable levels of resistance to carbapenems. Analysis of sequences surrounding the blaOXA-58 gene showed genetic variability, with the presence in several isolates of multiple copies of the blaOXA-58 gene; this extra copy number was likely related to an IS26-mediated transposition or recombination process.

Comparative Analysis of IncHI2 Plasmids Carrying blaCTX-M-2 or blaCTX-M-9 from Escherichia coli and Salmonella enterica Strains Isolated from Poultry and Humans

ABSTRACT Salmonella enterica bla CTX-M-2 and blaCTX-M-9 plasmid backbones from isolates from Belgium and France were analyzed. The blaCTX-M-2-plasmids from both human and poultry isolates were related to the IncHI2 pAPEC-O1-R plasmid, previously identified in the United States in avian Escherichia coli strains; the blaCTX-M-9 plasmids were closely related to the IncHI2 R478 plasmid.

First Report of the Carbapenem-Hydrolyzing Oxacillinase OXA-58 in Acinetobacter baumannii Isolates in Italy

Emergence of Acinetobacter baumannii with resistance or reduced susceptibility to carbapenems has been reported worldwide ([4][1]). Acinetobacter may develop resistance to carbapenems through various mechanisms, including decreased permeability, efflux pump overexpression, and production of