Energy deposition from focused terawatt laser pulses in air undergoing multifilamentation

Laser filamentation is responsible for the deposition of a significant part of the laser pulse energy in the propagation medium. We found that using terawatt laser pulses and relatively tight focusing conditions in air, resulting in a bundle of co-propagating multifilaments, more than 60 % of the pulses energy is transferred to the medium, eventually degrading into heat. This results in a strong hydrodynamic reaction of air with the generation of shock waves and associated underdense channels for each short-scale filament. In the focal zone, where filaments are close to each other, these discrete channels eventually merge to form a single cylindrical low-density tube over a $\sim 1 \mu\mathrm{s}$ timescale. We measured the maximum lineic deposited energy to be more than 1 J/m.Comment: 7 pages, 7 figure

Occurrence and genetic diversity of Salmonella in organic and conventional pig productions in France

The objectives of this study were 1) to assess the occurrence of Salmonella in organic pig production, in comparison with conventional pig production, 2) to evaluate the genetic diversity of strains isolated from these two productions and 3) to estimate the cross-contamination on slaughter line between conventional pig and organic pig. In one slaughterhouse, 26 organic herds and 31 conventional herds (2 pigs per herd) were sampled for Salmonella detection. Analyses were realized on colon content and swabs of carcass for each pig. Two isolates by positive samples were serotyped and typed by PFGE using XbaI enzyme. All S. Typhimurim and monophasic variant of serovar Typhimurium were subtyped by MLVA. Prevalence of Salmonella in colon content was higher for organic pigs, 37.9% IC95than for conventional pigs, 32.7% but difference was not significant (p=0.563). Salmonella prevalence was lowest on carcasses and very close between the two productions: 10.7% for organic and 10.3% for conventional. The 104 isolates were distributed in 7 serovars: Derby (46 isolates), Brandenburg (18), Typhimurium (13), monophasic variant of Typhimurium 4,12:i:- (11) and 4,5,12:i:- (10), Infantis (2) and Mbandaka (2). Sixteen PFGE profiles were obtained: 1 per serovar for serovars Mbandaka, Infantis, and Brandenbrug, 3 for Derby, 4 for Typhimurium and 4 for monophasic variant 4,12:i:-. Seven PFGE profiles, representing 84% of the isolates, were common between organic and conventional pigs. A major profile gathered 79% of the S. Derby strains. S. Brandenburg strains were also very clonal, all presented the same PFGE profiles whereas they came from 5 different herds. With 20 isolates from 12 carcasses, it has not been possible to show with certainty Salmonella cross-contamination between organic and conventional pigs during the process. For S. Typhimurium, MLVA gave a better discrimination than PFGE, 8 patterns against 4; particularly for 6 isolates with the same PFGE pattern which was subdivided into 5 MLVA patterns. While on the 21 monophasic isolates, MLVA and PFGE gave similar discrimination (7 patterns with MLVA and 6 with PFGE)

Prevalence and genetic diversity of Salmonella in organic and conventional pig productions in France

The objectives of this study were 1) to assess the occurrence of Salmonella in organic and conventional pig productions, 2) to evaluate the genetic diversity of strains isolated from these two productions, and 3) to estimate the cross-contamination on slaughter line between conventional pigs and organic pigs. 26 organic herds and 31 conventional herds were considered in one slaughterhouse. Two pigs per herds were sampled. For each pig, Salmonella detection was realized on colon content and swabs of carcass. Two isolates per positive samples were serotyped and genotyped by PFGE using XbaI enzyme. Prevalence of Salmonella in colon content was higher for organic pigs, 37,9% IC95%[25.5-51.6] than for conventional pigs, 32.7% IC95%[19.5-44.5] but it was not significantly different. Salmonella prevalence was lowest on carcasses and very close between the two productions; 10.7% IC95%[4.0-21.8] for organic carcasses and 10.3 IC95%[3.9-21.2]) for conventional carcasses. The 104 isolates were distributed in 7 serovars: Derby (46), , Brandenburg (18), Typhimurium (13), 2 types of monophasic variant of serovar Typhimurium 4,12:i:- (11) and 4,5,12:i:- (10), Infantis (2) and Mbandaka (2). Sixteen PFGE profiles were obtained: 1 per serovar for Mbandaka, Infantis, and Brandenbrug, 2 for monophasic variant 4,5,12:i:-, 3 for Derby, 4 for Typhimurium and 4 for monophasic variant 4,12:i:-. Seven PFGE profiles (84% of the strains) were common between organic and conventional pigs. A major profile gathered 79% of the S. Derby strains. S. Brandenburg strains presented only one PFGE profile which was detected in 5 different herds. It has not been possible to show with certainty Salmonella cross-contamination between organic and conventional pigs during the process. Indeed, only one S. Typhimurium PFGE profile was evidenced for organic and conventional carcasses during the same sampling day. This study gives for the first time data on Salmonella in organic pig production in France

Prolongation of the lifetime of guided discharges triggered in atmospheric air by femtosecond laser filaments up to 130 μs

International audienceThe triggering and guiding of electric discharges produced in atmospheric air by a compact 100 kV Marx generator is realized in laboratory using an intense femtosecond laser pulse undergoing filamentation. We describe here an approach allowing extending the lifetime of the discharges by injecting a current with an additional circuit. Laser guiding discharges with a length of 8.5 cm and duration of 130 μs were obtained

Long-lived laser-induced arc discharges for energy channeling applications

Abstract Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy

Development of An Innovative and Quick Method for the Isolation of Clostridium botulinum Strains Involved in Avian Botulism Outbreaks

International audienceAvian botulism is a serious neuroparalytic disease mainly caused by a type C/D botulinum neurotoxin produced by Clostridium botulinum group III, one of the entwined bacterial species from the Clostridium novyi sensu lato genospecies. Its isolation is very challenging due to the absence of selective media and the instability of the phage carrying the gene encoding for the neurotoxin. The present study describes the development of an original method for isolating C. botulinum group III strains. Briefly, this method consists of streaking the InstaGene matrix extraction pellet on Egg Yolk Agar plates and then collecting the colonies with lipase and lecithinase activities. Using this approach, it was possible to isolate 21 C. novyi sensu lato strains from 22 enrichment broths of avian livers, including 14 toxic strains. This method was successfully used to re-isolate type C, D, C/D, and D/C strains from liver samples spiked with five spores per gram. This method is cheap, user-friendly, and reliable. It can be used to quickly isolate toxic strains involved in avian botulism with a 64% success rate and C. novyi sensu lato with a 95% rate. This opens up new perspectives for C. botulinum genomic research, which will shed light on the epidemiology of avian botulism

Characterization of Campylobacter spp. transferred from naturally contaminated chicken legs to cooked chicken slices via a cutting board

International audienceCampylobacter represents the leading cause of gastroenteritis in Europe. Campylobacteriosis is mainly due to C. jejuni and C. coli. Poultry meat is the main source of contamination, and cross-contaminations in the consumer's kitchen appear to be the important route for exposure. The aim of this study was to examine the transfer of Campylobacter from naturally contaminated raw poultry products to a cooked chicken product via the cutting board and to determine the characteristics of the involved isolates. This study showed that transfer occurred in nearly 30% of the assays and that both the C. jejuni and C. coli species were able to transfer. Transfer seems to be linked to specific isolates: some were able to transfer during separate trials while others were not. No correlation was found between transfer and adhesion to inert surfaces, but more than 90% of the isolates presented moderate or high adhesion ability. All tested isolates had the ability to adhere and invade Caco-2 cells, but presented high variability between isolates. Our results highlighted the occurrence of Campylobacter cross-contamination via the cutting board in the kitchen. Moreover, they provided new interesting data to be considered in risk assessment studies. (C) 2013 Elsevier B.V. All rights reserved

Survie au froid et pathogénicité des souches de Yersinia enterocolitica BT4 isolées chez le porc et génétiquement proches ou non de souches isolées chez l’homme

International audienceThe aim of this study was to test the cold survival and pathogenicity of Yersinia enterocolitica BT4 strains isolated from pigs and genetically close or not to strains isolated from human cases, to assess their ability to pass through the food chain alive and infect humans. BT4 strains (n=50) of porcine origin (Anses and IFIP’s collections) and BT4 strains of human cases (n=50, CNR's collection) isolated in 2010 in France were sequenced. cgMLST, based on 1727 genes, was used to compare strains. Porcine strains and human strains in clusters were considered to be genetically closely related. Four porcine strains were selected: two closely related to human strains (P+H+), and two not (allelic difference > 9) (P+H-). The survival of these strains at 4°C was tested in BHI culture medium (5 Log10CFU/ml) and on ham (4.5 Log10CFU/cm2 ) for 10-11 days. Their pathogenicity was assessed using in vitro assays on human intestinal Caco-2 cells (105 cells/ml of Caco-2 cells for 107 bacteria/ml). During the survival test at 4°C, an increase of 4 Log10CFU/ml in BHI and of 1.5-2.0 Log10 CFU/cm2 on ham was observed for all strains. The P+H+ and P+H- strains did not differ significantly for the tests in BHI or on ham (P-value > 0.05). Adhesion and invasion on Caco-2 cells ranged from 65-90 % and 0.55-3.60 %, respectively. The P+H+ and P+H- strains did not differ significantly in pathogenicity. This study showed that the ability to survive and grow in cold conditions is not restricted to strains capable of infecting humans and that these strains had the same capacity to infect humans

Influence of operating conditions on the persistence of E. coli, enterococci, Clostridium perfringens and Clostridioides difficile in semi-continuous mesophilic anaerobic reactors

International audienceThis study examined the combined effect of hydraulic retention time (HRT), organic loading rate (OLR) and heat pretreatment of manure (70 degrees C, 1 h) on the fate of E. coli, enterococci, C. perfringens, C. difficile, and on chemical parameters (volatile fatty acids and ammonia) that may inactivate pathogens. Semi-continuous mesophilic anaerobic reactors were fed with pig manure and horse feed. The operating conditions were 2, 3, 4 COD.L-1.d(-1) (OLR), 24, 35, 46 days (HRT) and use or not of a thermal pretreatment. The levels of the chemical parameters did not reach concentrations capable of inactivating the four bacteria. Anaerobic digestion led to a Log io removal > 3 (E. coli), 0.9-2.1 (enterococci), 0.1-0.6 (C. perfringens) and 0-1 (C. difficile). Increasing HRT only reduced the concentration of E. coli in the digestate. Increasing OLR reduced the Log(10) removal of enterococci and C. difficile. The heat pretreatment led to non-detection of E. coli in the digestate, reduced the concentration of C. perfringens by 0.8-1.3 Log(10) and increased the concentration of C. difficile by 0.04-0.7 Log(10). Enterococci, not detected in the heated manure, were present in the digestate. The distribution of genes encoding virulence factors of C. difficile (tcdA and tcdB) and C. perfringens (cpa, cpb2 and cpb) was not impacted by anaerobic digestion or by the heat pretreatment. Enterococci, C. perfringens, C. difficile were present in the digestate at relatively stable concentrations regardless of the operating conditions, indicating that even with heat pretreatment, the biosafety of digestate cannot be guaranteed in mesophilic conditions

Development and validation of a new reliable method for the diagnosis of avian botulism

International audienceLiver is a reliable matrix for laboratory confirmation of avian botulism using real-time PCR. Here, we developed, optimized, and validated the analytical steps preceding PCR to maximize the detection of Clostridium botulinum group III in avian liver. These pre-PCR steps included enrichment incubation of the whole liver (maximum 25 g) at 37°C for at least 24 h in an anaerobic chamber and DNA extraction using an enzymatic digestion step followed by a DNA purification step. Conditions of sample storage before analysis appear to have a strong effect on the detection of group III C. botulinum strains and our results recommend storage at temperatures below -18°C. Short-term storage at 5°C is possible for up to 24 h, but a decrease in sensitivity was observed at 48 h of storage at this temperature. Analysis of whole livers (maximum 25 g) is required and pooling samples before enrichment culturing must be avoided. Pooling is however possible before or after DNA extraction under certain conditions. Whole livers should be 10-fold diluted in enrichment medium and homogenized using a Pulsifier® blender (Microgen, Surrey, UK) instead of a conventional paddle blender. Spiked liver samples showed a limit of detection of 5 spores/g liver for types C and D and 250 spores/g for type E. Using the method developed here, the analysis of 268 samples from 73 suspected outbreaks showed 100% specificity and 95.35% sensitivity compared with other PCR-based methods considered as reference. The mosaic type C/D was the most common neurotoxin type found in examined samples, which included both wild and domestic birds