Effectiveness of SplashGuard Caregiver prototype in reducing the risk of aerosol transmission in intensive care unit rooms of SARS-CoV-2 patients: a prospective and simulation study

BACKGROUND

The contagiousness of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is known to be linked to the emission of bioaerosols. Thus, aerosol-generating procedures (AGPs) could increase the risk of infection among healthcare workers (HCWs).

AIM

To investigate the impact of an aerosol protection box, the SplashGuard Caregiver (SGGC) with suction system, by direct analysis of the presence of viral particles after an AGP, and by using the computational fluid dynamics (CFD) simulation method.

METHODS

This prospective observational study investigated HCWs caring for patients with SARS-CoV-2 admitted to an intensive care unit (ICU). Rooms were categorized as: SGCG present and SGCG absent. Virus detection was performed through direct analysis, and using a CFD model to simulate the movement dynamics of airborne particles produced by a patient's respiratory activities.

FINDINGS

Of the 67 analyses performed, three samples tested positive on quantitative polymerase chain reaction: one of 33 analyses in the SCCG group (3%) and two of 34 analyses in the non-SGCG group (5.9%). CFD simulations showed that: (1) reduction of the gaps of an SGCG could decrease the number of emitted particles remaining airborne within the room by up to 70%; and (2) positioning HCWs facing the opposite direction to the main air flow would reduce their exposure.

CONCLUSIONS

This study documented the presence of SARS-CoV-2 among HCWs in a negative pressure ICU room of an infected patient with or without the use of an SGCG. The simulation will help to improve the design of the SGCG and the positioning of HCWs in the room.

Bacillus subtilis NDmed, a model strain for biofilm genetic studies

The Bacillus subtilis strain NDmed was isolated from an endoscope washer-disinfector in a medical environment. NDmed can form complex macrocolonies with highly wrinkled architectural structures on solid medium. In static liquid culture, it produces thick pellicles at the interface with air as well as remarkable highly protruding ''beanstalk-like'' submerged biofilm structures at the solid surface. Since these mucoid submerged structures are hyper-resistant to biocides, NDmed has the ability to protect pathogens embedded in mixed-species biofilms by sheltering them from the action of these agents. Additionally, this non-domesticated and highly biofilm forming strain has the propensity of being genetically manipulated. Due to all these properties, the NDmed strain becomes a valuable model for the study of B. subtilis biofilms. This review focuses on several studies performed with NDmed that have highlighted the sophisticated genetic dynamics at play during B. subtilis biofilm formation. Further studies in project using modern molecular tools of advanced technologies with this strain, will allow to deepen our knowledge on the emerging properties of multicellular bacterial life.

Polyhexamethylene biguanide promotes adaptive cross-resistance to gentamicin in Escherichia coli biofilms

Antimicrobial resistance is a critical public health issue that requires a thorough understanding of the factors that influence the selection and spread of antibiotic-resistant bacteria. Biocides, which are widely used in cleaning and disinfection procedures in a variety of settings, may contribute to this resistance by inducing similar defense mechanisms in bacteria against both biocides and antibiotics. However, the strategies used by bacteria to adapt and develop cross-resistance remain poorly understood, particularly within biofilms -a widespread bacterial habitat that significantly influences bacterial tolerance and adaptive strategies. Using a combination of adaptive laboratory evolution experiments, genomic and RT-qPCR analyses, and biofilm structural characterization using confocal microscopy, we investigated in this study how Escherichia coli biofilms adapted after 28 days of exposure to three biocidal active substances and the effects on cross-resistance to antibiotics. Interestingly, polyhexamethylene biguanide (PHMB) exposure led to an increase of gentamicin resistance (GenR) phenotypes in biofilms formed by most of the seven E. coli strains tested. Nevertheless, most variants that emerged under biocidal conditions did not retain the GenR phenotype after removal of antimicrobial stress, suggesting a transient adaptation (adaptive resistance). The whole genome sequencing of variants with stable GenR phenotypes revealed recurrent mutations in genes associated with cellular respiration, including cytochrome oxidase (cydA, cyoC) and ATP synthase (atpG). RT-qPCR analysis revealed an induction of gene expression associated with biofilm matrix production (especially curli synthesis), stress responses, active and passive transport and cell respiration during PHMB exposure, providing insight into potential physiological responses associated with adaptive crossresistance. In addition, confocal laser scanning microscopy (CLSM) observations demonstrated a global effect of PHMB on biofilm architectures and compositions formed by most E. coli strains, with the appearance of dense cellular clusters after a 24h-exposure. In conclusion, our results showed that the PHMB exposure stimulated the emergence of an adaptive cross-resistance to gentamicin in biofilms, likely induced through the activation of physiological responses and biofilm structural modulations altering gradients and microenvironmental conditions in the biological edifice.

Biofilms as protective cocoons against biocides: from bacterial adaptation to One Health issues

Bacteria in the food chain mostly live in communities associated with surfaces known as biofilms, which confer specific survival and adaptive abilities. In such communities, the bacteria mostly exhibit higher tolerance to external stress, and their recurrent exposure along the food chain to biocides used during cleaning and disinfection procedures raises concern about the adaptation routes they develop, both at single-cell and communal levels. In recent years, an increasing number of research subjects have focused on understanding the specific features of biofilms that enable bacterial populations to adapt to biocide exposure within a 'protective cocoon'. The first part of this review concentrates on the diversity of adaptive strategies, including structural modulation of these biofilms, physiological response or the acquisition of genetic resistance. The second part discusses the possible side effects of biofilm adaptation to biocides on antimicrobial cross-resistance, virulence and colonization features from a One Health perspective.

Presence and Depletion of Sulfadiazine, Trimethoprim, and Oxytetracycline into Feathers of Treated Broiler Chickens and Impact on Antibiotic-Resistant Bacteria

The valorization of poultry byproducts, like feathers (processed to feather meal), in animal feed could contribute to the presence of veterinary drugs, including antibiotics. An animal study was carried out to study the fate of sulfadiazine, trimethoprim, and oxytetracycline in feathers, plasma, and droppings of broiler chickens. Cage and floor housing, different from current farm practices, were studied. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A longer presence of antibiotics was observed in feathers compared to plasma, with sulfadiazine being present the most. The internal presence (via blood) and the external presence (via droppings) of antibiotics in/on feathers were shown. Analysis of Escherichia coli populations, from droppings and feathers, highlighted that resistant bacteria could be transferred from droppings to feathers in floor-housed animals. The overall results suggest that feathers are a potential reservoir of antimicrobial residues and could contribute to the selection of antibiotic-resistant bacteria in the environment, animals, and humans.

Genomic elements located in the accessory repertoire drive the adaptation to biocides in Listeria monocytogenes strains from different ecological niches

In response to the massive use of biocides for controlling Listeria monocytogenes (hereafter Lm) contaminations along the food chain, strains showing biocide tolerance emerged. Here, accessory genomic elements were associated with biocide tolerance through pangenome-wide associations performed on 197 Lm strains from different lineages, ecological, geographical and temporal origins. Mobile elements, including prophage-related loci, the Tn6188_qacH transposon and pLMST6_emrC plasmid, were widespread across lineage I and II food strains and associated with tolerance to benzalkonium-chloride (BC), a quaternary ammonium compound (QAC) widely used in food processing. The pLMST6_emrC was also associated with tolerance to another QAC, the didecyldimethylammonium-chloride, displaying a pleiotropic effect. While no associations were detected for chemically reactive biocides (alcohols and chlorines), genes encoding for cell-surface proteins were associated with BC or polymeric biguanide tolerance. The latter was restricted to lineage I strains from animal and the environment. In conclusion, different genetic markers, with polygenic nature or not, appear to have driven the Lm adaptation to biocide, especially in food strains but also from animal and the environment. These markers could aid to monitor and predict the spread of biocide tolerant Lm genotypes across different ecological niches, finally reducing the risk of such strains in food industrial settings.

FepR as a Central Genetic Target in the Adaptation to Quaternary Ammonium Compounds and Cross-Resistance to Ciprofloxacin in Listeria monocytogenes

The foodborne pathogen, Listeria monocytogenes, (Lm), frequently undergoes selection pressure associated with the extensive use of disinfectants, such as quaternary ammonium compounds, which are widely used in food processing plants. The repeated exposure to sub-inhibitory biocide concentrations can induce increased tolerance to these compounds, but can also trigger the development of antibiotic resistance, and both increase the risk of food contamination and persistence in food production environments. Although the acquisition of genes can explain biocide tolerance, the genetic mechanisms underlying the adaptive cross-resistance to antibiotics remain unclear. We previously showed that repeated exposure to benzalkonium chloride (BC) and didecyldimethyl ammonium chloride (DDAC) led to reduced susceptibility to ciprofloxacin in Lm strains from diverse sources. Here, we compared the genomes of 16 biocide-adapted and 10 parental strains to identify the molecular mechanisms of fluoroquinolone cross-resistance. A core genome SNP analysis identified various mutations in the transcriptional regulator fepR (lmo2088) for 94% of the adapted strains and mutations in other effectors at a lower frequency. FepR is a local repressor of the MATE fluoroquinolone efflux pump FepA. The impact of the mutations on the structure and function of the protein was assessed by performing in silico prediction and protein homology modeling. Our results show that 75% of the missense mutations observed in fepR are located in the HTH domain of the protein, within the DNA interaction site. These mutations are predicted to reduce the activity of the regulator, leading to the overexpression of the efflux pump responsible for the ciprofloxacin-enhanced resistance.

The coordinated population redistribution between Bacillus subtilis submerged biofilm and liquid-air pellicle

Bacillus subtilis is a widely used bacterial model to decipher biofilm formation, genetic determinants and their regulation. For several years, studies were conducted on colonies or pellicles formed at the interface with air, but more recent works showed that non-domesticated strains were able to form thick and structured biofilms on submerged surfaces. Taking advantage of time-lapse confocal laser scanning microscopy, we monitored bacterial colonization on the surface and observed an unexpected biphasic submerged biofilm development. Cells adhering to the surface firstly form elongated chains before being suddenly fragmented and released as free motile cells in the medium. This switching coincided with an oxygen depletion in the well which preceded the formation of the pellicle at the liquid-air interface. Residual bacteria still associated with the solid surface at the bottom of the well started to express matrix genes under anaerobic metabolism to build the typical biofilm protruding structures.

Microbial Biofilms: Structural Plasticity and Emerging Properties

Microbial biofilms are found everywhere and can be either beneficial or detrimental, as they are involved in crucial ecological processes and in severe chronic infections. The functional properties of biofilms are closely related to their three-dimensional (3D) structure, and the ability of microorganisms to collectively and dynamically shape the community spatial organization in response to stresses in such biological edifices. A large number of works have shown a relationship between the modulation of the spatial organization and ecological interactions in biofilms in response to environmental fluctuations, as well as their emerging properties essential for nutrient cycling and bioremediation processes in natural environments. On the contrary, numerous studies have emphasized the role of structural rearrangements and matrix production in the increased tolerance of bacteria in biofilms toward antimicrobials. In these last few years, the development of innovative approaches, relying on recent technological advances in imaging, computing capacity, and other analytical tools, has led to the production of original data that have improved our understanding of this close relationship. However, it has also highlighted the need to delve deeper into the study of cell behavior in such complex communities during 3D structure development and maturation- from a single-cell to a multicellular scale- to better control or harness positive and negative impacts of biofilms. For this Special Issue, the interplay between biofilm emerging properties and their 3D spatial organization considering different models, from single bacteria to complex environmental communities, and various environments, from natural ecosystems to industrial and medical settings are addressed.

Comparison of the Genetic Features Involved in Bacillus subtilis Biofilm Formation Using Multi-Culturing Approaches

Surface-associated multicellular assemblage is an important bacterial trait to withstand harsh environmental conditions. Bacillus subtilis is one of the most studied Gram-positive bacteria, serving as a model for the study of genetic pathways involved in the different steps of 3D biofilm formation. B. subtilis biofilm studies have mainly focused on pellicle formation at the air-liquid interface or complex macrocolonies formed on nutritive agar. However, only few studies focus on the genetic features of B. subtilis submerged biofilm formation and their link with other multicellular models at the air interface. NDmed, an undomesticated B. subtilis strain isolated from a hospital, has demonstrated the ability to produce highly structured immersed biofilms when compared to strains classically used for studying B. subtilis biofilms. In this contribution, we have conducted a multi-culturing comparison (between macrocolony, swarming, pellicle, and submerged biofilm) of B. subtilis multicellular communities using the NDmed strain and mutated derivatives for genes shown to be required for motility and biofilm formation in pellicle and macrocolony models. For the 15 mutated NDmed strains studied, all showed an altered phenotype for at least one of the different culture laboratory assays. Mutation of genes involved in matrix production (i.e., tasA, epsA-O, cap, ypqP) caused a negative impact on all biofilm phenotypes but favored swarming motility on semi-solid surfaces. Mutation of bslA, a gene coding for an amphiphilic protein, affected the stability of the pellicle at the air-liquid interface with no impact on the submerged biofilm model. Moreover, mutation of lytF, an autolysin gene required for cell separation, had a greater effect on the submerged biofilm model than that formed at aerial level, opposite to the observation for lytABC mutant. In addition, B. subtilis NDmed with sinR mutation formed wrinkled macrocolony, less than that formed by the wild type, but was unable to form neither thick pellicle nor structured submerged biofilm. The results are discussed in terms of the relevancy to determine whether genes involved in colony and pellicle formation also govern submerged biofilm formation, by regarding the specificities in each model.

Exposure to Quaternary Ammonium Compounds Selects Resistance to Ciprofloxacin in Listeria monocytogenes

In this contribution, the antimicrobial susceptibility toward 11 antibiotics and four biocides of a panel of 205 Listeria monocytogenes (Lm) strains isolated from different ecological niches (i.e., food, animals and natural environment) was evaluated. The impact of exposure to biocides on the antibiotic susceptibilities of Lm was also investigated. Lm strains isolated from food exhibited overall a lower susceptibility (higher minimal inhibitory concentrations, MIC) for ammonium quaternary compounds (QACs) and peracetic acid (PAC) than strains isolated from animals and natural environments. Conversely, the ecological origins of Lm strains did not significantly affect their susceptibilities towards antibiotics. Interestingly, repeated exposure to QACs recurrently led to a decrease in susceptibility toward ciprofloxacin (CIP), a fluoroquinolone antibiotic, largely used in human medicine. Moreover, these lower levels of susceptibility to CIP remained stable in most Lm strains even after subcultures without biocide selection pressure, suggesting an adaptation involving modifications at the genetic level. Results underlined the ability of Lm to adapt to biocides, especially QACs, and the potential link between this adaptation and the selection of resistance toward critical antibiotics such as ciprofloxacin. These data support a potential role of the extensive use of QACs from "farm to fork" in the selection of biocide and antibiotic resistance in pathogenic bacteria such as Lm.

Emergence of a Synergistic Diversity as a Response to Competition in Pseudomonas putida Biofilms

Genetic diversification through the emergence of variants is one of the known mechanisms enabling the adaptation of bacterial communities. We focused in this work on the adaptation of the model strain Pseudomonas putida KT2440 in association with another P. putida strain (PCL1480) recently isolated from soil to investigate the potential role of bacterial interactions in the diversification process. On the basis of colony morphology, three variants of P. putida KT2440 were obtained from co-culture after 168 h of growth whereas no variant was identified from the axenic KT2440 biofilm. The variants exhibited distinct phenotypes and produced biofilms with specific architecture in comparison with the ancestor. The variants better competed with the P. putida PCL1480 strain in the dual-strain biofilms after 24 h of co-culture in comparison with the ancestor. Moreover, the synergistic interaction of KT2440 ancestor and the variants led to an improved biofilm production and to higher competitive ability versus the PCL1480 strain, highlighting the key role of diversification in the adaptation of P. putida KT2440 in the mixed community. Whole genome sequencing revealed mutations in polysaccharides biosynthesis protein, membrane transporter, or lipoprotein signal peptidase genes in variants.

Biorefinery for heterogeneous organic waste using microbial electrochemical technology

Environmental biorefineries aim to produce biofuels and platform biomolecules from organic waste. To this end, microbial electrochemical technologies theoretically allow controlled microbial electrosynthesis (MES) of organic molecules to be coupled to oxidation of waste. Here, we provide a first proof of concept and a robust operation strategy for MES in a microbial electrolysis cell (MEC) fed with biowaste hydrolysates. This strategy allowed stable operation at 5 A/m² for more than three months in a labscale reactor. We report a two to four-fold reduction in power consumption compared to microbial electrosynthesis with water oxidation at the anode. The bioelectrochemical characterizations of the cells were used to compute energy and matter balances for biorefinery scenarios in which anaerobic digestion (AD) provides the electricity and CO₂ required for the MEC. Calculations shows that up to 22% of electrons (or COD) from waste may be converted to organic products in the AD-MEC process.

Impact of cleaning and disinfection procedures on microbial ecology and Salmonella antimicrobial resistance in a pig slaughterhouse

To guarantee food safety, a better deciphering of ecology and adaptation strategies of bacterial pathogens such as Salmonella in food environments is crucial. The role of food processing conditions such as cleaning and disinfection procedures on antimicrobial resistance emergence should especially be investigated. In this work, the prevalence and antimicrobial resistance of Salmonella and the microbial ecology of associated surfaces communities were investigated in a pig slaughterhouse before and after cleaning and disinfection procedures. Salmonella were detected in 67% of samples and isolates characterization revealed the presence of 15 PFGE-patterns belonging to five serotypes: S.4,5,12:i:-, Rissen, Typhimurium, Infantis and Derby. Resistance to ampicillin, sulfamethoxazole, tetracycline and/or chloramphenicol was detected depending on serotypes. 16S rRNA-based bacterial diversity analyses showed that Salmonella surface associated communities were highly dominated by the Moraxellaceae family with a clear site-specific composition suggesting a persistent colonization of the pig slaughterhouse. Cleaning and disinfection procedures did not lead to a modification of Salmonella susceptibility to antimicrobials in this short-term study but they tended to significantly reduce bacterial diversity and favored some genera such as Rothia and Psychrobacter. Such data participate to the construction of a comprehensive view of Salmonella ecology and antimicrobial resistance emergence in food environments in relation with cleaning and disinfection procedures.

Spatial Organization Plasticity as an Adaptive Driver of Surface Microbial Communities

Biofilms are dynamic habitats which constantly evolve in response to environmental fluctuations and thereby constitute remarkable survival strategies for microorganisms. The modulation of biofilm functional properties is largely governed by the active remodeling of their three-dimensional structure and involves an arsenal of microbial self-produced components and interconnected mechanisms. The production of matrix components, the spatial reorganization of ecological interactions, the generation of physiological heterogeneity, the regulation of motility, the production of actives enzymes are for instance some of the processes enabling such spatial organization plasticity. In this contribution, we discussed the foundations of architectural plasticity as an adaptive driver of biofilms through the review of the different microbial strategies involved. Moreover, the possibility to harness such characteristics to sculpt biofilm structure as an attractive approach to control their functional properties, whether beneficial or deleterious, is also discussed.

Whole Proteome Analyses on Ruminiclostridium cellulolyticum Show a Modulation of the Cellulolysis Machinery in Response to Cellulosic Materials with Subtle Differences in Chemical and Structural Properties

Lignocellulosic materials from municipal solid waste emerge as attractive resources for anaerobic digestion biorefinery. To increase the knowledge required for establishing efficient bioprocesses, dynamics of batch fermentation by the cellulolytic bacterium Ruminiclostridium cellulolyticum were compared using three cellulosic materials, paper handkerchief, cotton discs and Whatman filter paper. Fermentation of paper handkerchief occurred the fastest and resulted in a specific metabolic profile: it resulted in the lowest acetate-to-lactate and acetate-to-ethanol ratios. By shotgun proteomic analyses of paper handkerchief and Whatman paper incubations, 151 proteins with significantly different levels were detected, including 20 of the 65 cellulosomal components, 8 non-cellulosomal CAZymes and 44 distinct extracytoplasmic proteins. Consistent with the specific metabolic profile observed, many enzymes from the central carbon catabolic pathways had higher levels in paper handkerchief incubations. Among the quantified CAZymes and cellulosomal components, 10 endoglucanases mainly from the GH9 families and 7 other cellulosomal subunits had lower levels in paper handkerchief incubations. An in-depth characterization of the materials used showed that the lower levels of endoglucanases in paper handkerchief incubations could hypothetically result from its lower crystallinity index (50%) and degree of polymerization (970). By contrast, the higher hemicellulose rate in paper handkerchief (13.87%) did not result in the enhanced expression of enzyme with xylanase as primary activity, including enzymes from the “xyl-doc” cluster. It suggests the absence, in this material, of molecular structures that specifically lead to xylanase induction. The integrated approach developed in this work shows that subtle differences among cellulosic materials regarding chemical and structural characteristics have significant effects on expressed bacterial functions, in particular the cellulolysis machinery, resulting in different metabolic patterns and degradation dynamics.

Biocathodes reducing oxygen at high potential select biofilms dominated by Ectothiorhodospiraceae populations harboring a specific association of genes

Biocathodes polarized at high potential are promising for enhancing Microbial Fuel Cell performances but the microbes and genes involved remain poorly documented. Here, two sets of five oxygen-reducing biocathodes were formed at two potentials (-0.4V and +0.1V vs. saturated calomel electrode) and analyzed combining electrochemical and metagenomic approaches. Slower start-up but higher current densities were observed at high potential and a distinctive peak increasing over time was recorded on cyclic voltamogramms, suggesting the growth of oxygen reducing microbes. 16S pyrotag sequencing showed the enrichment of two operational taxonomic units (OTUs) affiliated to Ectothiorodospiraceae on high potential electrodes with the best performances. Shotgun metagenome sequencing and a newly developed method for the identification of Taxon Specific Gene Annotations (TSGA) revealed Ectothiorhodospiraceae specific genes possibly involved in electron transfer and in autotrophic growth. These results give interesting insights into the genetic features underlying the selection of efficient oxygen reducing microbes on biocathodes.

Fluorescence-based tools for single-cell approaches in food microbiology

The better understanding of the functioning of microbial communities is a challenging and crucial issue in the field of food microbiology, as it constitutes a prerequisite to the optimization of positive and technological microbial population functioning, as well as for the better control of pathogen contamination of food. Heterogeneity appears now as an intrinsic and multi-origin feature of microbial populations and is a major determinant of their beneficial or detrimental functional properties. The understanding of the molecular and cellular mechanisms behind the behavior of bacteria in microbial communities requires therefore observations at the single-cell level in order to overcome "averaging" effects inherent to traditional global approaches. Recent advances in the development of fluorescence-based approaches dedicated to single-cell analysis provide the opportunity to study microbial communities with an unprecedented level of resolution and to obtain detailed insights on the cell structure, metabolism activity, multicellular behavior and bacterial interactions in complex communities. These methods are now increasingly applied in the field of food microbiology in different areas ranging from research laboratories to industry. In this perspective, we reviewed the main fluorescence-based tools used for single-cell approaches and their concrete applications with specific focus on food microbiology.

Comparison of synthetic medium and wastewater used as dilution medium to design scalable microbial anodes: Application to food waste treatment

The objective was to replace synthetic medium by wastewater as a strategy to design low-cost scalable bioanodes. The addition of activated sludge was necessary to form primary bioanodes that were then used as the inoculum to form the secondary bioanodes. Bioanodes formed in synthetic medium with acetate 10mM provided current densities of 21.9±2.1A/m(2), while bioanodes formed in wastewater gave 10.3±0.1A/m(2). The difference was explained in terms of biofilm structure, electrochemical kinetics and redox charge content of the biofilms. In both media, current densities were straightforwardly correlated with the biofilm enrichment in Geobacteraceae but, inside this family, Geobacter sulfurreducens and an uncultured Geobacter sp. were dominant in the synthetic medium, while growth of another Geobacter sp. was favoured in wastewater. Finally, the primary/secondary procedure succeeded in designing bioanodes to treat food wastes by using wastewater as dilution medium, with current densities of 7±1.1A/m(2).

Biofilm-associated persistence of food-borne pathogens

Microbial life abounds on surfaces in both natural and industrial environments, one of which is the food industry. A solid substrate, water and some nutrients are sufficient to allow the construction of a microbial fortress, a so-called biofilm. Survival strategies developed by these surface-associated ecosystems are beginning to be deciphered in the context of rudimentary laboratory biofilms. Gelatinous organic matrices consisting of complex mixtures of self-produced biopolymers ensure the cohesion of these biological structures and contribute to their resistance and persistence. Moreover, far from being just simple three-dimensional assemblies of identical cells, biofilms are composed of heterogeneous sub-populations with distinctive behaviours that contribute to their global ecological success. In the clinical field, biofilm-associated infections (BAI) are known to trigger chronic infections that require dedicated therapies. A similar belief emerging in the food industry, where biofilm tolerance to environmental stresses, including cleaning and disinfection/sanitation, can result in the persistence of bacterial pathogens and the recurrent cross-contamination of food products. The present review focuses on the principal mechanisms involved in the formation of biofilms of food-borne pathogens, where biofilm behaviour is driven by its three-dimensional heterogeneity and by species interactions within these biostructures, and we look at some emergent control strategies.

Contribution of confocal laser scanning microscopy in deciphering biofilm tridimensional structure and reactivity

Confocal laser scanning microscopy (CLSM) became in last years an invaluable technique to study biofilms since it enables researchers to explore noninvasively the dynamic architecture and the reactivity of these biological edifices. The constant development of fluorescent markers and genetic tools along with the improvement of spatial, spectral, and temporal resolution of imaging facilities offers new opportunities to better decipher microbial biofilm properties. In this contribution, we proposed to describe the contribution of CLSM to the study of biofilm architecture and reactivity throughout two different illustrative approaches.

A model-based approach to detect interspecific interactions during biofilm development

A model-based approach was developed to detect interspecific interactions during biofilm development. This approach relied on the comparison of experimental data with a simple null model of biofilm growth dynamics where individual species grew independently of one another, except that they competed for space. Such a model was directly parameterized with a 4D confocal image series of biofilms and then used as a null model to detect interspecific interactions between pairs of bacterial species. This approach was tested in two bispecific competitive trials. In the first trial, the progressive exclusion of Pseudomonas fluorescens by Pseudomonas putida appeared to be due solely to the different intrinsic growth rates of the two strains. In contrast, modelling results suggested the presence of interference competition between Pseudomonas aeruginosa and P. putida in mixed biofilms. The authors' approach enables the detection of ecologically relevant interactions which constitute a prerequisite to building a comprehensive view of the dynamics and functioning of spatially structured bacterial communities.

Realistic representation of Bacillus subtilis biofilms architecture using combined microscopy (CLSM, ESEM and FESEM)

In this contribution, we used a set of microscopic techniques including confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM) and field emission scanning electron microscopy (FESEM) to analyze the three-dimensional spatial arrangement of cells and their surrounding matrix in Bacillus subtilis biofilm. The combination of the different techniques enabled a deeper and realistic deciphering of biofilm architecture by providing the opportunity to overcome the limits of each single technique.

Anisotropic nutrient transport in three-dimensional single species bacterial biofilms

The ability for a biofilm to grow and function is critically dependent on the nutrient availability, and this in turn is dependent on the structure of the biofilm. This relationship is therefore an important factor influencing biofilm maturation. Nutrient transport in bacterial biofilms is complex; however, mathematical models that describe the transport of particles within biofilms have made three simplifying assumptions: the effective diffusion coefficient (EDC) is constant, the EDC is that of water, and/or the EDC is isotropic. Using a Monte Carlo simulation, we determined the EDC, both parallel to and perpendicular to the substratum, within 131 real, single species, three-dimensional biofilms that were constructed from confocal laser scanning microscopy images. Our study showed that diffusion within bacterial biofilms was anisotropic and depth dependent. The heterogeneous distribution of bacteria varied between and within species, reducing the rate of diffusion of particles via steric hindrance. In biofilms with low porosity, the EDCs for nutrient transport perpendicular to the substratum were significantly lower than the EDCs for nutrient transport parallel to the substratum. Here, we propose a reaction-diffusion model to describe the nutrient concentration within a bacterial biofilm that accounts for the depth dependence of the EDC.

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.

Comparative biocidal activity of peracetic acid, benzalkonium chloride and ortho-phthalaldehyde on 77 bacterial strains

Despite numerous reports on biocide activities, it is often difficult to have a reliable and relevant overview of bacterial resistance to disinfectants because each work challenges a limited number of strains and tested methods are often different. The aim of this study was to evaluate the bactericidal activity of three different disinfectants commonly used in industrial or medical environments (peracetic acid, benzalkonium chloride and ortho-phthalaldehyde) against 77 bacterial strains from different origins using one standard test method (NF EN 1040). Results highlight the existence of high interspecific variability of resistance to disinfectants and, contrary to widespread belief, Gram-positive strains generally appeared more resistant than Gram-negative strains. Resistance was also variable among strains of the same species such as Bacillus subtilis to peracetic acid, Pseudomonas aeruginosa to benzalkonium chloride and Staphylococcus aureus to ortho-phthalaldehyde.

The spatial architecture of Bacillus subtilis biofilms deciphered using a surface-associated model and in situ imaging

The formation of multicellular communities known as biofilms is the part of bacterial life cycle in which bacteria display cooperative behaviour and differentiated phenotypes leading to specific functions. Bacillus subtilis is a Gram-positive bacterium that has served for a decade as a model to study the molecular pathways that control biofilm formation. Most of the data on B. subtilis biofilms have come from studies on the formation of pellicles at the air-liquid interface, or on the complex macrocolonies that develop on semi-solid nutritive agar. Here, using confocal laser scanning microcopy, we show that B. subtilis strains of different origins are capable of forming biofilms on immersed surfaces with dramatically protruding "beanstalk-like" structures with certain strains. Indeed, these structures can reach a height of more than 300 µm with one undomesticated strain from a medical environment. Using 14 GFP-labeled mutants previously described as affecting pellicle or complex colony formation, we have identified four genes whose inactivation significantly impeded immersed biofilm development, and one mutation triggering hyperbiofilm formation. We also identified mutations causing the three-dimensional architecture of the biofilm to be altered. Taken together, our results reveal that B. subtilis is able to form specific biofilm features on immersed surfaces, and that the development of these multicellular surface-associated communities involves regulation pathways that are common to those governing the formation of pellicle and/or complex colonies, and also some specific mechanisms. Finally, we propose the submerged surface-associated biofilm as another relevant model for the study of B. subtilis multicellular communities.

Thyroid volume measurement in external beam radiotherapy patients using CT imaging: correlation with clinical and anthropometric characteristics

The aim of this study is to define criteria for accurate representation of the thyroid in human models used to represent external beam radiotherapy (EBRT) patients and evaluate the relationship between the volume of this organ and clinical and anthropometric characteristics. From CT images, we segmented the thyroid gland and calculated its volume for a population of 188 EBRT patients of both sexes, with ages ranging from 1 to 89 years. To evaluate uncertainties linked to measured volumes, experimental studies on the Livermore anthropomorphic phantom were performed. For our population of EBRT patients, we observed that in children, thyroid volume increased rapidly with age, from about 3 cm(3) at 2 years to about 16 cm(3) at 20. In adults, the mean thyroid gland volume was 23.5 ± 9 cm(3) for males and 17.5 ± 8 cm(3) for females. According to anthropometric parameters, the best fit for children was obtained by modeling the log of thyroid volume as a linear function of body surface area (BSA) (p < 0.0001) and age (p = 0.04) and for adults, as a linear function of BSA (p < 0.0001) and gender (p = 0.01). This work enabled us to demonstrate that BSA was the best indicator of thyroid volume for both males and females. These results should be taken into account when modeling the volume of the thyroid in human models used to represent EBRT patients for dosimetry in retrospective studies of the relationship between the estimated dose to the thyroid and long-term follow-up data on EBRT patients.

The biofilm architecture of sixty opportunistic pathogens deciphered using a high throughput CLSM method

This study proposes a high throughput method based on Confocal Laser Scanning Microscopy (CLSM) combined with the use of 96-wells microtiter plates compatible with high resolution imaging for the study of biofilm formation and structure. As an illustration, the three-dimensional structures of biofilms formed by 60 opportunistic pathogens were thus observed and quantified. The results revealed the diversity of biofilm architectures. Specific spatial arrangement such as the mushroom-like structures already described for Pseudomonas aeruginosa was observed. Other features, such as hollow voids in microcolonies of Salmonella enterica strain Agona, were identified for the first time. The combined use of microplates and confocal imaging proved to be a good alternative to the other high throughput methods commonly used as it enables the direct, insitu, qualitative and quantitative characterization of biofilm architecture. This high content method should lead to a clearer understanding of the structure-function relationships implicated in biofilms traits.

[Quality control of dosing delivered by in vivo measurements for head and neck radiotherapy]

PURPOSE

Measurement of absorbed dose in target volume is widely considered to be an important tool for quality assurance in external radiotherapy. The aims of this work were to measure the entrance dose for patient treated for head and neck tumors and to compare this measured dose with the dose calculated.

PATIENTS AND METHODS

Twenty patients were evaluated. Initially, the measurements were performed on a polystyrene phantom in order to calibrate diodes in terms of entrance dose and to determinate appropriate correction factors. In vivo entrance dosimetry check was performed for these patients treated for head and neck tumors in (60)Co gamma-rays.

RESULTS

For the entrance dose evaluation over 100 field measurements, the mean deviation between the measured dose and the calculated dose was equal to 0.12% and the standard deviation was 1.84%. The deviation was less than 3% in 95% of measurements. Large deviation (more than 5%) was observed in one case.

CONCLUSION

Simple in vivo dose measurements are an additional safeguard against major set-up errors and calculation or transcription errors that were missed during pretreatment chart check.

Multichannel dosemeter and Al2O3:C optically stimulated luminescence fibre sensors for use in radiation therapy: evaluation with electron beams

This article proposes an innovative multichannel optically stimulated luminescence (OSL) dosemeter for on-line in vivo dose verification in radiation therapy. OSL fibre sensors incorporating small Al(2)O(3):C fibre crystals (TLD(500)) have been tested with an X-ray generator. A reproducible readout procedure should reduce the fading-induced uncertainty ( approximately - 1% per decade). OSL readouts are temperature-dependent [ approximately 0.3% K(-1) when OSL stimulation is performed at the same temperature as irradiation; approximately 0.16% K(-1) after thermalisation (20 degrees C)]. Sensor calibration and depth-dose measurements with electron beams have been performed with a Saturne 43 linear accelerator in reference conditions at CEA-LNHB (ionising radiation reference laboratory in France). Predosed OSL sensors show a good repeatability in multichannel operation and independence versus electron energy in the range (9, 18 MeV). The difference between absorbed doses measured by OSL and an ionisation chamber were within +/-0.9% (for a dose of about 1 Gy) despite a sublinear calibration curve.

Épidermolyse staphylococcique et impétigo bulleux chez des jumeaux nouveau-nés contaminés par le lait maternel

Staphylococcus aureus is often responsible for late septic infections, more rarely of toxinic ones, occurring in neonatal period. We report a case of staphylococcal scalded skin syndrome and bullous impetigo in newborn twins infected by breast milk from their asymptomatic mother. This transmission was confirmed by molecular biology method. This case emphasizes the potential part of the mother in staphylococcal nosocomial infections and the complexity of toxinic mechanisms.

Impact of PSA decrease at the end of radiotherapy for localized prostate cancer on clinical recurrence and specific cause survival

15501

Background: The objective was to identify early predictors of outcome in a large retrospective series of patients treated by external beam radiotherapy only (without androgen deprivation). All the patients had a PSA at the 6th week (PSA6wRT) in the course of RT. Methods: From 1990 to 2004, 409 pts with localized prostate cancer were treated by RT. Median pretreatment PSA (PSApreRT) was 13 ng/mL (0.5–133). Clinical stage was T1 (26%), T2 (60%), and T3 (14%). Gleason score was 4–6 (59%), 7 (31%) and 8–10 (10%). Prognosis was classified as low risk (24%), intermediate (39%) and high risk (37%). The prostate received 65 Gy (2.5 Gy/day) (34%) or 70 Gy (2 or 2.5 Gy/day) (66%). Results: The median follow-up was 57 months (6–190). The median ratio of : PSA6wRT / PSApreRT was 71% (1–374). The 5-year biochemical disease free survival (DFS) rates (RTOG-ASTRO 2006) by PSA6wRT / PSApreRT < 71% or ≥ 71% were: 66% (95% CI: 58–74) and 56% (95% CI: 48–64), respectively (Log rank, p=0.048),. The 5-year clinical (local or metastases) DFS rates by PSA6wRT / PSApreRT < 71% or ≥ 71% were: 96% (95% CI: 93–99) and 85% (95% CI: 79–91), respectively (p=0.03). In multivariate analysis, the prognostic values of PSA6wRT / PSApreRT (as a continuous variable) on biochemical DFS, clinical DFS and cause specific survival are shown in the table . Conclusions: The PSA6wRT / PSApreRT predicts for biochemical DFS, clinical DFS and cause specific survival in localized prostate cancer. This factor could be used to propose adjuvant treatment after radiotherapy, in case of high: PSA6wRT / PSApreRT.

[Table: see text]

No significant financial relationships to disclose.

Recommandations pour un protocole d’assurance de qualité de la radiothérapie conformationnelle avec modulation d’intensité des cancers de la tête et du cou

Head and neck tumors represent very interesting targets for IMRT techniques because of the complex shape of the structures and the organs at risk close by. The use of this kind of techniques requires a quality assurance protocol. The physicists of the GORTEC group shared their experience to define some recommendations in order to draw up a QA protocol. The dosimetric verification of the treatment plans (in terms of absolute and relative dose), the control of the reproducibility of the patient positioning and the use of a record and verify system to control the different parameters form the main parts of these recommendations. Each chapter comprises a description of the different methods, recommendations concerning the equipment, the adopted tolerances, the frequency of controls. At the end of each chapter, a table summarizes the main actions to carry out. These recommendations will allow to harmonize our practices whatever the softwares and the accelerator that are being used. They will simplify the task of the teams that wish to implement IMRT for head and neck tumors.

[Influence of thermoplastic masks on the absorbed skin dose for head and neck tumor radiotherapy]

The influence of thermoplastic masks used in clinical routine for patient immobilization in head and neck radiotherapy treatment on the absorbed skin dose has been investigated at Gustave-Roussy Institute. The measurements were performed in 60Co gamma-rays, 4 and 6MV X-rays and in 8 and 10MeV electron beams. Initially, the measurements were performed with thermoluminescent dosimeters (LiF) and a NACP chamber on a polystyrene phantom in order to study the influence of physical parameters (distance, field size, energy...) on first millimeters depth variation dose. The study was completed with in vivo measurements on 14 patients using various dosimeters (thermoluminescent detectors, diodes) in order to assess the increase of dose on first millimeters depth and to verify the delivered dose during treatment sessions (quality control). In treatment conditions, masks lead to an important increase of dose on the first millimeter in 60Co gamma-rays beams (dose value normalized to maximum of dose increase from 57.1% to 77.7% for 0.5 mm-water depth and from 78.5% to 88% for 1 mm-water depth); its contribution is less important in 4 and 6 MV X-rays beams (dose value normalized to maximum of dose increase from 49.5% to 63.2% for 0.5 mm-water depth and from 59% to 70.1% for 1 mm-water depth). Concerning 8 and 10 MeV electron beams, the normalized dose value increase respectively from 78.4% to 81.7% and from 82.2% to 86.1% for 0.5 mm-water depth. In vivo dosimetry enabled the quality control of delivered dose during treatment. Measured dose is in agreement within +/- 5% with the prescribed dose for 92.3% of cases. In routine, in vivo dosimetry allowed to quantify the increase of skin dose induced by thermoplastic masks for various energies of photon and electron beams as well as quality control.

Influence of high-energy photon beam irradiation on pacemaker operation

In this paper, we determine the influence of high-energy photon beam irradiation used for external radiotherapy on pacemakers, at different doses and dose rates. Ninety-six pacemakers of various origins and ages underwent in vitro high-energy photon irradiation under technical conditions close to external radiotherapy, using a linear accelerator delivering photons of high energy (18 MV). Various dose levels (up to 200 Gy for certain particularly resistant pacemakers) were delivered to pacemakers located in a water-equivalent phantom with several dose rates (from 0.05 to 8 Gy min(-1)). Observed failures were sorted into eight classes of progressive harmfulness, some of them possibly lethal. One irradiated pacemaker exhibited an important defect at a dose rate of 0.2 Gy min(-1), for a cumulative dose of 0.15 Gy. Two pacemakers showed an important defect at a cumulative dose of 1 Gy, while nine pacemakers failed at a cumulative dose lower than or equal to 2 Gy and 13 failed at a cumulative dose lower than or equal to 5 Gy. The most important failure probability (70% of irradiated pacemakers) is observed for 8 Gy min(-1), whereas no pacemakers failed at a dose rate lower than or equal to 0.2 Gy min(-1). In conclusion, warnings given by manufacturers about the maximum tolerable cumulative radiation doses for safe operation of irradiated pacemakers (5 Gy), even reduced to 2 Gy, are not reliable. The spread of cumulative doses inducing failures is very large since our observations show an important failure at 0.15 Gy, while ten pacemakers withstood more than 140 Gy of cumulative dose. The safe operation of pacemakers under irradiation depends mainly on type and model. It depends also on dose rate. From our observations, for the safe operation of pacemakers, a recommendation of a maximum dose rate of 0.2 Gy min(-1) rejecting direct irradiation of the pacemaker at a standard dose rate for tumour treatment (2 Gy min(-1)) is made.

[Definition of volumes in external radiotherapy: ICRU reports 50 and 62]

Prescribing and achieving radiotherapy require accurate definitions of the target volumes and of the dose to be delivered in them. The need for the availability of a coherent vocabulary, recognized from local to international levels, has justified the publication, by the ICRU, of two reports related to external radiotherapy, the Report 50 (1993) and the Report 62 (1999). This paper presents the main propositions of the ICRU for the definition of the volumes, as well as comments and recommendations for their use.