We report a theoretical investigation of the electrohydrodynamic properties of spherical soft particles composed of permeable concentric layers that differ in thickness, soft material density, chemical composition, and flow penetration degree. Starting from a recent numerical scheme developed for the computation of the direct-current electrophoretic mobility (mu) of diffuse soft bioparticles, the dependence of mu on the electrolyte concentration and solution pH is evaluated taking the known three-layered structure of bacteriophage MS2 as a supporting model system (bulk RNA, RNA-protein bound layer, and coat protein). The electrokinetic results are discussed for various layer thicknesses, hydrodynamic flow penetration degrees, and chemical compositions, and are discussed on the basis of the equilibrium electrostatic potential and hydrodynamic flow field profiles that develop within and around the structured particle. This study allows for identifying the cases where the electrophoretic mobility is a function of the inner structural and chemical specificity of the particle and not only of its outer surface properties. Along these lines, we demonstrate the general inapplicability of the notions of zeta potential (zeta) and surface charge for quantitatively interpreting electrokinetic data collected for such systems. We further shed some light on the physical meaning of the isoelectric point. In particular, numerical and analytical simulations performed on structured soft layers in indifferent electrolytic solution demonstrate that the isoelectric point is a complex ionic strength-dependent signature of the flow permeation properties and of the chemical and structural details of the particle. Finally, the electrophoretic mobilities of the MS2 virus measured at various ionic strength levels and pH values are interpreted on the basis of the theoretical formalism aforementioned. It is shown that the electrokinetic features of MS2 are to a large extent determined not only by the external proteic capsid but also by the chemical composition and hydrodynamic flow permeation of/within the inner RNA-protein bound layer and bulk RNA part of the bacteriophage. The impact of virus aggregation, as revealed by decreasing diffusion coefficients for decreasing pH values, is also discussed.

Summary Temperature is considered as the major factor determining virus inactivation in the environment. Food industries, therefore, widely apply temperature as virus inactivating parameter. This review encompasses an overview of viral inactivation and virus genome degradation data from published literature as well as a statistical analysis and the development of empirical formulae to predict virus inactivation. A total of 658 data (time to obtain a first log10 reduction) were collected from 76 published studies with 563 data on virus infectivity and 95 data on genome degradation. Linear model fitting was applied to analyse the effects of temperature, virus species, detection method (cell culture or molecular methods), matrix (simple or complex) and temperature category (<50 and ≥50°C). As expected, virus inactivation was found to be faster at temperatures ≥50°C than at temperatures <50°C, but there was also a significant temperature–matrix effect. Virus inactivation appeared to occur faster in complex than in simple matrices. In general, bacteriophages PRD1 and PhiX174 appeared to be highly persistent whatever the matrix or the temperature, which makes them useful indicators for virus inactivation studies. The virus genome was shown to be more resistant than infectious virus. Simple empirical formulas were developed that can be used to predict virus inactivation and genome degradation for untested temperatures, time points or even virus strains.

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Several microbes and chemicals have been considered as potential tracers to identify fecal sources in the environment. However, to date, no one approach has been shown to accurately identify the origins of fecal pollution in aquatic environments. In this multilaboratory study, different microbial and chemical indicators were analyzed in order to distinguish human fecal sources from nonhuman fecal sources using wastewaters and slurries from diverse geographical areas within Europe. Twenty-six parameters, which were later combined to form derived variables for statistical analyses, were obtained by performing methods that were achievable in all the participant laboratories: enumeration of fecal coliform bacteria, enterococci, clostridia, somatic coliphages, F-specific RNA phages, bacteriophages infecting Bacteroides fragilis RYC2056 and Bacteroides thetaiotaomicron GA17, and total and sorbitol-fermenting bifidobacteria; genotyping of F-specific RNA phages; biochemical phenotyping of fecal coliform bacteria and enterococci using miniaturized tests; specific detection of Bifidobacterium adolescentis and Bifidobacterium dentium; and measurement of four fecal sterols. A number of potentially useful source indicators were detected (bacteriophages infecting B. thetaiotaomicron, certain genotypes of F-specific bacteriophages, sorbitol-fermenting bifidobacteria, 24-ethylcoprostanol, and epycoprostanol), although no one source identifier alone provided 100% correct classification of the fecal source. Subsequently, 38 variables (both single and derived) were defined from the measured microbial and chemical parameters in order to find the best subset of variables to develop predictive models using the lowest possible number of measured parameters. To this end, several statistical or machine learning methods were evaluated and provided two successful predictive models based on just two variables, giving 100% correct classification: the ratio of the densities of somatic coliphages and phages infecting Bacteroides thetaiotaomicron to the density of somatic coliphages and the ratio of the densities of fecal coliform bacteria and phages infecting Bacteroides thetaiotaomicron to the density of fecal coliform bacteria. Other models with high rates of correct classification were developed, but in these cases, higher numbers of variables were required.Determining the source of fecal contamination in aquatic environments is essential for estimating the health risks associated with pollution, facilitating measures to remediate polluted waterways, and resolving legal responsibility for remediation. Source tracking methods should enable investigators to uncover the sources of fecal pollution in a particular water body (40). Candidate microbes and chemicals have been investigated and reviewed (15,54,55) as potential tools for the identification of human fecal sources. More recently, new approaches using eukaryotic mitochondrial DNA to differentiate fecal sources in feces-contaminated surface waters have been explored (43). However, field ...

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Bacteriophages infecting Bacteroides are potentially a good tool for fecal source tracking, but different Bacteroides host strains are needed for different geographic areas. A feasible method for isolating Bacteroides host strains for phages present in human fecal material is described. Useful strains were identified for application in Spain and the United Kingdom. One strain, GA-17, identified as Bacteroides thetaiotaomicron, was tested in several locations in Europe with excellent performance in Southern Europe.Microbial source tracking methods are designed to enable researchers to uncover the sources of fecal pollution in a water body (19). Bacteriophages infecting Bacteroides are potential tools for microbial source tracking (4,13,22,24,26,29). However, it is well documented that Bacteroides host strains vary in their ability to discriminate between phages of different sources but also that phage detection by a given host strain varies geographically. Thus, Bacteroides fragilis strain HSP40 detects good numbers of phages in different areas of the Mediterranean region (4,9,10,28,29,30) and in South Africa (12), but it fails to detect significant numbers of phages in Northern Europe (22) and the United States (15). In contrast, other strains, such as RYC 2056, detect similar numbers of phages in different geographical areas but do not discriminate between the sources of fecal pollution (5,7,18,22). Strains tested in the United States to date appear to behave like RYC 2056 (15).Limitations of existing source tracking methods (19,24,25,26,27), combined with the good source tracking performance of strain HSP40 in certain geographical areas (4,9,12,28,30), along with increasing information about the specificity between the animal host and the bacteria of the Bacteroides group (11, 32) and the narrow host ranges reported for phages infecting Bacteroides (6,8,16,22,30), prompted our search for new Bacteroides host strains.We describe here a rapid method for isolating and further testing Bacteroides host strains potentially useful for source tracking.Isolation of new hosts for phages infecting Bacteroides. Four trials for isolation of Bacteroides strains from raw municipal sewage from Spain (two trials), Colombia (one trial), and the United Kingdom (one trial) were carried out by two independent operators.Decimal dilutions of sewage samples were plated onto Bacteroides bile esculine agar (17) and incubated at 36°C (Ϯ2°C) for 44 (Ϯ4) h in anaerobic jars. Anaerobiosis was achieved with commercial anaerobic generators (Merck KGaA, Darmstadt, Germany). Black colonies with a black or dark halo (17) were picked and plated for pure culture on Bacteroides bile esculine agar plates incubated under aerobic and anaerobic conditions (anaerobic jars). Gram staining of isolates growing only under anaerobic conditions was carried out. Gram-negative obligate anaerobic rods isolated at this stage (level 1 isolates) (Table 1) were further processed. They were grown in BPRM broth at 36°C (Ϯ2°C) for 18 (Ϯ2) h in anaerobic conditions. Ba...

We compare for the first time the electrokinetic and aggregation properties of MS2 phage (pH 2.5 to 7, 1 to 100 mM NaNO 3 electrolyte concentration) with those of the corresponding virus-like particles (VLPs), which lack entirely the inner viral RNA component. In line with our previous work (J. Langlet, F. Gaboriaud, C. Gantzer, and J. F. L. Duval, Biophys. J. 94:3293-3312, 2008), it is found that modifying the content of RNA within the virus leads to very distinct electrohydrodynamic and aggregation profiles for MS2 and MS2 VLPs. Under the given pH and concentration conditions, MS2 VLPs exhibit electrophoretic mobility larger in magnitude than that of MS2, and both have similar isoelectric point (IEP) values (ϳ4). The electrokinetic results reflect a greater permeability of MS2 VLPs to electroosmotic flow, developed within/around these soft particles during their migration under the action of the applied electrical field. Results also support the presence of some remaining negatively charged component within the VLPs. In addition, MS2 phage systematically forms aggregates at pH values below the IEP, regardless of the magnitude of the solution ionic strength, whereas MS2 VLPs aggregate under the strict condition where the pH is relatively equal to the IEP at sufficiently low salt concentrations (<10 mM). It is argued that the stability of VLPs against aggregation and the differences between electrokinetics of MS2 and corresponding VLPs conform to recently developed formalisms for the stability and electrohydrodynamics of soft multilayered particles. The differences between the surface properties of these two kinds of particles reported here suggest that VLPs may not be appropriate for predicting the behavior of pathogenic viruses in aqueous media.Understanding the behavior of virus particles of enteric pathogens (e.g., norovirus, hepatitis A virus) in terms of aggregation or adhesion is mandatory for addressing appropriately the processes involved in, e.g., viral dissemination or water treatment (9, 11). In that respect, much effort is now devoted to the analysis of the so-called surface properties of viruses, which are impacted by solution pH, ionic strength, or the presence of organic matter (20). The importance of viral surface properties within the framework of water treatment is well illustrated by the relationship between the efficiency of membrane filtration for removing viruses and the charge and degree of hydrophobicity of these biocolloids (11).According to standard formulations of Derjaguin-LandauVerwey-Overbeek (DLVO) representation and electrokinetic theories for hard (impermeable) particles, a parameter commonly used as an indicator for the sign and magnitude of charge carried by a virus in a solution of given pH is the difference between the pH and the so-called isoelectric point (IEP) of the virus, defined as the pH value at which virus electrophoretic mobility is zero (14). Within the regime of partial dissociation of charges located at the surface, the higher (or lower) the solution pH is than ...

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