The influence of the accessory genome on bacterial pathogen evolution

Bacterial pathogens exhibit significant variation in their genomic content of virulence factors. This reflects the abundance of strategies pathogens evolved to infect host organisms by suppressing host immunity. Molecular arms-races have been a strong driving force for the evolution of pathogenicity, with pathogens often encoding overlapping or redundant functions, such as type III protein secretion effectors and hosts encoding ever more sophisticated immune systems. The pathogens’ frequent exposure to other microbes, either in their host or in the environment, provides opportunities for the acquisition or interchange of mobile genetic elements. These DNA elements accessorise the core genome and can play major roles in shaping genome structure and altering the complement of virulence factors. Here, we review the different mobile genetic elements focusing on the more recent discoveries and highlighting their role in shaping bacterial pathogen evolution

Characterization of the IncA/C plasmid pCC416 encoding VIM-4 and CMY-4 β-lactamases

Objectives: To characterize the antibiotic resistance regions of pCC416, a VIM-4- and CMY-4-encoding plasmid from clinical enterobacteria, and to elucidate its relation with the CMY-encoding plasmids widely diffused in Salmonella. Methods: The enterobacterial multiresistant plasmid pCC416 was derived from an Escherichia coli transconjugant and characterized. Conventional and long-range PCR assays were performed using primers specific for VIM-4- and CMY-4-encoding segments of pCC416. Amplicons were characterized by sequencing. blaVIM-4, blaMY-4 and IntI1-specific probes were prepared from PCR products and used for the identification of various pCC416 clones. VIM- and CMY-positive Bam HI and Sau 3AI fragments of pCC416 were cloned into pACYC184 and their sequences were determined by gene walking. Results: The pCC416 plasmid contained two distinct resistant loci carrying β-lactamase genes. The blaVIM-4 gene was part of an integron located in a complex, multidrug-resistant region of novel structure, interspersed with mobile elements or remnants thereof and being similar to various regions of other resistance plasmids. Nevertheless, a region in the 3′ end of this structure resembled the respective region found in a CMY-2-encoding plasmid from Salmonella. The blaCMY-4 gene was identified within an 11.3 kb region also related to the CMY-2-encoding plasmids. Conclusions: pCC416 probably evolved from an IncA/C2, CMY-encoding plasmid through acquisition of a VIM-encoding In4-type integron providing an example of accretion of resistance determinants in a single replicon. © The Author 2007

Characterization of the IncA/C plasmid pCC416 encoding VIM-4 and CMY-4 β-lactamases

Objectives: To characterize the antibiotic resistance regions of pCC416, a VIM-4- and CMY-4-encoding plasmid from clinical enterobacteria, and to elucidate its relation with the CMY-encoding plasmids widely diffused in Salmonella. Methods: The enterobacterial multiresistant plasmid pCC416 was derived from an Escherichia coli transconjugant and characterized. Conventional and long-range PCR assays were performed using primers specific for VIM-4- and CMY-4-encoding segments of pCC416. Amplicons were characterized by sequencing. blaVIM-4, blaMY-4 and IntI1-specific probes were prepared from PCR products and used for the identification of various pCC416 clones. VIM- and CMY-positive Bam HI and Sau 3AI fragments of pCC416 were cloned into pACYC184 and their sequences were determined by gene walking. Results: The pCC416 plasmid contained two distinct resistant loci carrying β-lactamase genes. The blaVIM-4 gene was part of an integron located in a complex, multidrug-resistant region of novel structure, interspersed with mobile elements or remnants thereof and being similar to various regions of other resistance plasmids. Nevertheless, a region in the 3′ end of this structure resembled the respective region found in a CMY-2-encoding plasmid from Salmonella. The blaCMY-4 gene was identified within an 11.3 kb region also related to the CMY-2-encoding plasmids. Conclusions: pCC416 probably evolved from an IncA/C2, CMY-encoding plasmid through acquisition of a VIM-encoding In4-type integron providing an example of accretion of resistance determinants in a single replicon. © The Author 2007

Replicon typing of plasmids encoding resistance to newer beta-lactams.

8reservedmixedCARATTOLI A; MIRIAGOU V; BERTINI A; LOLI A; COLINON C; VILLA L; WHICHARD . JM; G. ROSSOLINICarattoli, A; Miriagou, V; Bertini, A; Loli, A; Colinon, C; Villa, L; Whichard., Jm; Rossolini, GIAN MARI

Emergence in Klebsiella pneumoniae and Enterobacter cloacae clinical isolates of the VIM-4 metallo-beta-lactamase encoded by a conjugative plasmid

Resistance to carbapenems is an emerging problem among gram-negative hospital pathogens. A transferable plasmid encoding the VIM-4 metallo-beta-lactamase was detected in isolates of Klebsiella pneumoniae and Enterobacter cloacae obtained from a single patient under carbapenem therapy. Thus, enterobacteria appear to increasingly contribute to the spread of VIM-type enzymes

The bacterial thiopurine methyltransferase tellurite resistance process is highly dependent upon aggregation properties and oxidative stress response

International audienceBacterial thiopurine methyltransferases (bTPMTs) can favour resistance towards toxic tellurite oxyanions through a pathway leading to the emission of a garlic-like smell. Gene expression profiling completed by genetic, physiological and electron microscopy analyses was performed to identify key bacterial activities contributing to this resistance process. Escherichia coli strain MG1655 expressing the bTPMT was used as a cell model in these experiments. This strain produced a garlic-like smell which was found to be due to dimethyl telluride, and cell aggregates in culture media supplemented with tellurite. Properties involved in aggregation were correlated with cell attachment to polystyrene, which increased with tellurite concentrations. Gene expression profiling supported a role of adhesins in the resistance process with 14% of the tellurite-regulated genes involved in cell envelope, flagella and fimbriae biogenesis. Other tellurite-regulated genes were, at 27%, involved in energy, carbohydrate and amino acid metabolism including the synthesis of antioxidant proteins, and at 12% in the synthesis of transcriptional regulators and signal transduction systems. Escherichia coli mutants impaired in tellurite-regulated genes showed ubiquinone and adhesins synthesis, oxidative stress response, and efflux to be essential in the bTPMT resistance process. High tellurite resistance required a synergistic expression of these functions and an efficient tellurium volatilization by the bTPMT