Listeria monocytogenes in Milk Products

peer-reviewedMilk and milk products are frequently identified as vectors for transmission of Listeria monocytogenes. Milk can be contaminated at farm level either by indirect external contamination from the farm environment or less frequently by direct contamination of the milk from infection in the animal. Pasteurisation of milk will kill L. monocytogenes, but post-pasteurisation contamination, consumption of unpasteurised milk and manufacture of unpasteurised milk products can lead to milk being the cause of outbreaks of listeriosis. Therefore, there is a concern that L. monocytogenes in milk could lead to a public health risk. To protect against this risk, there is a need for awareness surrounding the issues, hygienic practices to reduce the risk and adequate sampling and analysis to verify that the risk is controlled. This review will highlight the issues surrounding L. monocytogenes in milk and milk products, including possible control measures. It will therefore create awareness about L. monocytogenes, contributing to protection of public health

The sedimentation of colloidal nanoparticles in solution and its study using quantitative digital photography

Sedimentation and diffusion are important aspects of the behavior of colloidalnanoparticles in solution, and merit attention during the synthesis, characterization, and application of nanoparticles. Here, the sedimentation of nanoparticles is studied quantitatively using digital photography and a simple model based on the Mason–Weaver equation. Good agreement between experimental time-lapse photography and numerical solutions of the model is found for a series of gold nanoparticles. The new method is extended to study for the first time the gravitational sedimentation of DNA-linked gold nanoparticle dimers as a model system of a higher complexity structure. Additionally, simple formulas are derived for estimating suitableparameters for the preparative centrifugation of nanoparticle solutions

Linear and non-linear optical spectroscopy of 'well-behaved' colloidal suspensions of nanocrystal assemblies

International audienceThe directed self-assembly of nanocrystals in the liquid phase can yield new materials with interesting optical properties for potential applications in medical diagnostics, phototherapy, photoenergy, and the guiding of light. Development of self-assembly strategies for such materials require clear relations between the generated structures and their optical properties. It is therefore useful to study the spectroscopy of nanocrystal assemblies in their native colloidal suspension.If a suspension of nanoparticles obeys established models of how colloidal suspensions behave in terms of diffusion[1], sedimentation and dependence of aggregation state on liquid phase composition, spectroscopic parameters of the suspended nanoparticles can be determined quantitatively in real-time, giving access to their dynamic behaviour and information during their functional performance. In this presentation we will show the spectroscopic methods that we utilise for the characterisation of colloidal plasmonic nanoparticle suspensions. These consist of steady-state methods (such as resonant light scattering[2]), as well as time-correlated spectroscopies[3] that work at the single-particle level, and even allow for recording of spectra of single particles diffusing in suspension[4,5]. We will present our latest developments concerning the measurement of extinction and scattering cross sections of plasmonic nano-objects, the diffusion and sedimentation behaviour of plasmonic colloids, and the intrinsic photoluminescence of various advanced gold nanoparticle assemblies (such as DNA-linked gold nanoparticles[6]). This plasmon-mediated luminescence is observed under both monophotonic or multiphoton excitation.[1] M. H. V. Werts, V. Raimbault, R. Texier-Picard, R. Poizat, O. Français, L. Griscom, J. R. G. Navarro. Lab Chip 2012, 12, 808.[2] J. R. G. Navarro, M. H. V. Werts, Analyst 2013, 138, 583. [3] M. Loumaigne, R. Praho, D. Nutarelli, M. H. V. Werts, A. Débarre. Phys. Chem. Chem. Phys. 2010, 12, 11004.[4] M. Loumaigne, P. Vasanthakumar, A. Richard, A. Débarre. ACS Nano 2012, 6, 10512.[5] M. Loumaigne, J. R. G. Navarro, S. Parola, M. H. V. Werts, A. Débarre, Nanoscale 2015, 7, 9013.[6] P. K. Harimech, S. R. Gerrard, A. H. El-Sagheer, T. Brown, A. G. Kanaras, J. Am. Chem. Soc. 2015, 137, 9242

Ethidium and propidium monoazide: comparison of potential toxicity on <i>Vibrio</i> sp. viability

International audienceSignificance and Impact of the Study: Ethidium monoazide (EMA) and propidium monoazide (PMA) treatment have commonly been used combined with qPCR to discriminate viable and dead cells. However, these DNA-binding dyes can damage membranes in viable bacteria, generating false-negative results. Most available studies examined either EMA-qPCR or PMA-qPCR, based on the literature to select the dye of interest. However, none of them tested the cytotoxicity of EMA vs PMA on various Vibrio sp. strains. In this study, we showed that PMA was the optimal dye for Vibrio as a tool for pretreatment when using qPCR methods to determine Vibrio viability in environmental or seafood samples