Identification of Novel Linear Megaplasmids Carrying a ß-Lactamase Gene in Neurotoxigenic Clostridium butyricum Type E Strains

Since the first isolation of type E botulinum toxin-producing Clostridium butyricum from two infant botulism cases in Italy in 1984, this peculiar microorganism has been implicated in different forms of botulism worldwide. By applying particular pulsed-field gel electrophoresis run conditions, we were able to show for the first time that ten neurotoxigenic C. butyricum type E strains originated from Italy and China have linear megaplasmids in their genomes. At least four different megaplasmid sizes were identified among the ten neurotoxigenic C. butyricum type E strains. Each isolate displayed a single sized megaplasmid that was shown to possess a linear structure by ATP-dependent exonuclease digestion. Some of the neurotoxigenic C. butyricum type E strains possessed additional smaller circular plasmids. In order to investigate the genetic content of the newly identified megaplasmids, selected gene probes were designed and used in Southern hybridization experiments. Our results revealed that the type E botulinum neurotoxin gene was chromosome-located in all neurotoxigenic C. butyricum type E strains. Similar results were obtained with the 16S rRNA, the tetracycline tet(P) and the lincomycin resistance protein lmrB gene probes. A specific mobA gene probe only hybridized to the smaller plasmids of the Italian C. butyricum type E strains. Of note, a ß-lactamase gene probe hybridized to the megaplasmids of eight neurotoxigenic C. butyricum type E strains, of which seven from clinical sources and the remaining one from a food implicated in foodborne botulism, whereas this ß-lactam antibiotic resistance gene was absent form the megaplasmids of the two soil strains examined. The widespread occurrence among C. butyricum type E strains associated to human disease of linear megaplasmids harboring an antibiotic resistance gene strongly suggests that the megaplasmids could have played an important role in the emergence of C. butyricum type E as a human pathogen

Analysis of the Unsteady Flow Around a Hydrofoil at Various Incidences

The oscillating hydrofoils used in underwater propulsion devices often experience large variations of the flow incidence, which favors cavitation at large angle of attack, and therefore a severe degradation of the performance, additional flow instability, and even cavitation erosion. These various phenomena make numerical simulations of the flow around oscillating hydrofoils quite challenging, especially in cases where the laminar-turbulent transition usually occurs when the blade has a high angle of attack. In the present study, the unsteady flow around a stationary Clark-Y hydrofoil is simulated at five fix incidence angles using the Star CCM+ software. The results show that the lift coefficient increases continuously with the incidence angle up to 15°, even after a separation vortex is generated near the trailing edge. Then, as a slight stall occurs at 20°, the lift coefficients obtained with the k-ω SST and SST Re teta transition models become significantly different, mostly because of the different prediction of laminar to turbulence transition at the hydrofoil leading edge. Under deep stall condition at 25°, the flow is much more complex and the hydrofoil performance decreases dramatically. The lift force predicted by the SST transition model is more periodic than with the SST k-ω model. Although the general vortex evolution predicted by the two turbulence models is similar, the local pressure experiences larger amplitude variations with the k-ω SST model, as can be also observed from the evolution of the lift coefficient