Biofilm Growth Phases Research Articles

Study on the chemical composition and anti-fungi activities of anthraquinones and its glycosides from Rumex japonicus Houtt.

Fungi, such as Trichophyton rubrum (T. rubrum) and Microsporum canis Bodin Anamorph (M. canis Bodin Anamorph) are the main pathogens of dermatophysis. According to ancient books records, Rumex japonicus Houtt. (RJH) has a miraculous effect on the treatment of dermatophysis. To reveal the anti-fungi (T. rubrum and M. canis Bodin Anamorph) components and its mechanism of the Rumex japonicus Houtt. The vinegar extraction and alcohol precipitation, HPLC and nuclear magnetic resonance spectroscopy (NMR) were employed for analyzing the chemical compositions of RJH; in vitro anti-fungal experiment was investigated including test the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC), spore germination rate, nucleic acid, protein leakage rate, biofilm structure, and the mechanism of anti-fungal and anti-fungal biofilms in RJH. Seven anthraquinones and their glycoside compounds were obtained in this study respectively, such as chrysophanol, physcion, aloe-emodin, emodin, rhein, emodin-8-O-β-D-glucoside and chrysophanol-8-O-β-D-glucoside. In vitro anti-fungal experiment results showed that RJH extracts have good anti-fungal activity for dermatophytic fungi. Among them, the MIC of the rhein, emodin and aloe-emodin against T. rubrum are 1.9µg/ml, 3.9µg/ml and 15.6µg/ml, respectively; the MIC of emodin and aloe-emodin against M. canis Bodin Anamorph are 7.8µg/ml and 62.5µg/ml, respectively. In addition, its active components can inhibit fungal spore germination and the formation of bud tube, change cell membrane permeability, prevent hyphal growth, destroy biofilm structure, and down-regulate the expression of agglutinin-like sequence family 1 of the adhesion phase of biofilm growth. The study shows that RJH play a fungicidal role.

Decoding the role of oxidative stress resistance and alternative carbon substrate assimilation in the mature biofilm growth mode of Candida glabrata

BackgroundBiofilm formation is viewed as a vital mechanism in C. glabrata pathogenesis. Although, it plays a significant role in virulence but transcriptomic architecture and metabolic pathways governing the biofilm growth mode of C. glabrata remain elusive. The present study intended to investigate the genes implicated in biofilm growth phase of C. glabrata through global transcriptomic approach.ResultsFunctional analysis of Differentially expressed genes (DEGs) using gene ontology and pathways analysis revealed that upregulated genes are involved in the glyoxylate cycle, carbon-carbon lyase activity, pre-autophagosomal structure membrane and vacuolar parts whereas, down- regulated genes appear to be associated with glycolysis, ribonucleoside biosynthetic process, ribosomal and translation process in the biofilm growth condition. The RNA-Seq expression of eight selected DEGs (CgICL1, CgMLS1, CgPEP1, and CgNTH1, CgERG9, CgERG11, CgTEF3, and CgCOF1) was performed with quantitative real-time PCR (RT-qPCR). The gene expression profile of selected DEGs with RT-qPCR displayed a similar pattern of expression as observed in RNA-Seq. Phenotype screening of mutant strains generated for genes CgPCK1 and CgPEP1, showed that Cgpck1∆ failed to grow on alternative carbon substrate (Glycerol, Ethanol, Oleic acid) and similarly, Cgpep1∆ unable to grow on YPD medium supplemented with hydrogen peroxide. Our results suggest that in the absence of glucose, C. glabrata assimilate glycerol, oleic acid and generate acetyl coenzyme-A (acetyl-CoA) which is a central and connecting metabolite between catabolic and anabolic pathways (glyoxylate and gluconeogenesis) to produce glucose and fulfil energy requirements.ConclusionsThe study was executed using various approaches (transcriptomics, functional genomics and gene deletion) and it revealed that metabolic plasticity of C. glabrata (NCCPF-100,037) in biofilm stage modulates its virulence and survival ability to counter the stress and may promote its transition from commensal to opportunistic pathogen. The observations deduced from the present study along with future work on characterization of the proteins involved in this intricate process may prove to be beneficial for designing novel antifungal strategies.

Monitoring silica core@shell nanoparticle-bacterial film interactions using the multi-parametric surface plasmon resonance technique.

In a healthcare setting, biofilms are a major source of infection and difficult to eradicate once formed. Nanoparticles (NPs) can be designed to effectively penetrate biofilms to more efficiently either deliver antibiotic drugs throughout the biofilm matrix or elicit inherent antibiofilm activity. Antibacterial cerium oxide (CeO2) NPs were employed as core material and coated with a mesoporous silica shell (MSN) to generate cerium oxide coated mesoporous silica NPs (CeO2@MSN). Detailed studies of NP-biofilm interactions are required to rationally develop NP platforms to prevent biofilm-related infections. This work developed and implemented a unique label-free analysis platform for the real-time monitoring of bacterial biofilm formation and then assessed the interactions of antibacterial NPs. An analysis platform which allows bacterial biofilms to grow and develop in situ in flow within the multi-parametric surface plasmon resonance (MP-SPR) instrument was established. This enabled simultaneous monitoring and detection of biofilm growth phases, structure, and interactions between differentially charged CeO2@MSNs and bacterial biofilms. Positively charged antibacterial NPs (polyethyleneimine functionalized CeO2@MSNs) were found to be the most efficient to penetrate the biofilm. The MP-SPR analysis platform was shown to be a powerful tool for monitoring biofilm development in real-time and to analyze biofilm properties and NP-biofilm interactions.

Amoeba & Biofilms in UK Chlorinated Drinking Water Distributions Systems: Impact on Water Safety

Amoeba-related diseases have been related with the presence of certain amoebas in domestic water, including drinking water. Biofilms in drinking water distribution systems are able to support amoeba growth by providing a food source and protecting them against disinfectants. Additionally, amoeba growth can be favoured by warm temperatures and climate change appears to contribute to its geographic spread. The presence of amoeba and its association with potential pathogenic bacteria was studied in a real-scale chlorinated DWDS. The test facility comprised three independent pipe loops fed with water from the local water supply and for this study a varied flow hydraulic profile was applied based on daily patterns observed in real UK distribution networks. The daily regime was repeated for a biofilm growth phase of 30 days. Amoeba viability was tested by a culture-based method, non-nutrient agar (NNA)-E. coli plates, and then confirm by qPCR using specific primers to detect species of amoeba including Naegleria and Acanthamoeba. Amplicon sequencing of the 16s rRNA gene was used to characterise the biofilm and planktonic bacterial communities. Several amoeba species belonging to the genera Acanthamoeba, Vermamoeba and Naegleria were identified in 30-day old biofilm samples. While the bacterial communities in biofilms were dominated by Variovorax, Pseudomonas and Aquabacterium. This study yielded new insights on the dynamics of amoeba and bacterial communities in DWDS. However, more research is required to accurately establish the impact of these inter-kingdom associations on human health.

First Report on the Phenotypic and Genotypic Susceptibility Profiles to Silver Nitrate in Bacterial Strains Isolated from Infected Leg Ulcers in Romanian Patients

Silver-ion-based antiseptics are widely used in treating chronic leg ulcers and, given the emergence of resistance to such compounds, the investigation of silver susceptibility and resistance profiles of pathogenic strains isolated from this type of wound is a topic of great interest. Therefore, in this study, 125 bacterial strains isolated from 103 patients with venous ulcers were investigated to elucidate their susceptibility to silver-nitrate solutions in planktonic and biofilm growth states, and the associated genetic determinants. The isolated strains, both in the planktonic and biofilm growth phases, showed high sensitivity to the standard concentration of 1/6000 silver-nitrate solution. It was noticed that even at concentrations lower than the clinical one (the first 2–3 binary dilutions in the case of planktonic cultures and the first 6–7 binary dilutions in the case of biofilms), the antiseptic solution proved to maintain its antibacterial activity. The phenotypic results were correlated with the genetic analysis, highlighting the presence of silver-resistance genes (sil operon) in only a few of the tested Staphylococcus sp. (especially in S. aureus) strains, Escherichia coli and Pseudomonas aeruginosa strains. These results demonstrate that despite its large use, this antiseptic remains a viable treatment alternative for the management of chronic leg wounds.

Characterization of the biofilm grown on 304L stainless steel in urban wastewaters: extracellular polymeric substances (EPS) and bacterial consortia

Characterization of the biofilm growing on stainless steel (SS) in untreated (UTUWW) and treated (TUWW) urban wastewaters was performed. In both media, the first phase of biofilm growth was aerobic, when the genera Caldimonas, Caulobacter, Terriglobus and Edaphobacter (iron oxidizing bacteria [IOB]) and the genera Bacillus, Sulfurimonas, Syntrophobacter and Desulfobacter (sulfur oxidizing bacteria [SOB]) were identified. In the second phase, established after immersion for 7 days, the high amount of EPS inhibited the access of oxygen and promoted the growth of anaerobic bacteria, which were the genus Shewanella (iron-reducing bacterium [IRB]) and the genera Desulfovirga, Desulfovibrio, Desulfuromusa, Desulfococcus, and Desulfosarcina (sulfate-reducing bacteria [SRB]). Electrochemical measurements showed that in the first stage, the aerobic bacteria and the high amount of EPS delayed the cathodic reduction of oxygen. However, in the second stage, EPS and the anaerobic bacteria promoted anodic dissolution.

Silver Nanoantibiotics Display Strong Antifungal Activity Against the Emergent Multidrug-Resistant Yeast Candida auris Under Both Planktonic and Biofilm Growing Conditions.

Candida auris is an emergent multidrug-resistant pathogenic yeast with an unprecedented ability for a fungal organism to easily spread between patients in clinical settings, leading to major outbreaks in healthcare facilities. The formation of biofilms by C. auris contributes to infection and its environmental persistence. Most antifungals and sanitizing procedures are not effective against C. auris, but antimicrobial nanomaterials could represent a viable alternative to combat the infections caused by this emerging pathogen. We have previously described an easy and inexpensive method to synthesize silver nanoparticles (AgNPs) in non-specialized laboratories. Here, we have assessed the antimicrobial activity of the resulting AgNPs on C. auris planktonic and biofilm growth phases. AgNPs displayed a strong antimicrobial activity against all the stages of all C. auris strains tested, representative of four different clades. Under planktonic conditions, minimal inhibitory concentration (MIC) values of AgNPs against the different strains were <0.5 μg ml−1; whereas calculated IC50 values for inhibition of biofilms formation were <2 μg ml−1 for all, but one of the C. auris strains tested. AgNPs were also active against preformed biofilms formed by all different C. auris strains, with IC50 values ranging from 1.2 to 6.2 μg ml−1. Overall, our results indicate potent activity of AgNPs against strains of C. auris, both under planktonic and biofilm growing conditions, and indicate that AgNPs may contribute to the control of infections caused by this emerging nosocomial threat.

Laboratory study of interactions between copper and microorganisms in oxic groundwater

The interactions between copper, the canister material in the nuclear waste disposal concept in Finland and Sweden, and micro-organisms in groundwater in their expected near-field environment are the core interest of this paper. Copper specimens were incubated with ammonia-oxidising bacteria for different time periods and then subjected to electrochemical measurements and surface characterisation to provide data on biofilm formation and its effects on copper corrosion. The biofilms on the surface of copper specimens were heterogeneous, due to the morphology of corrosion products that developed during the biofilm growth phase, but they also contributed to the nature and amount of corrosion product layers on the copper surfaces. Nitrogen was systematically detected in the biofilm specimens, due to the presence of ammonia-oxidising bacteria. The electrochemical response of the specimens was so heavily linked with the detected corrosion products, often rich in chlorine from the groundwater, that the influence of ammonia-oxidising bacteria was masked. The results demonstrate that the role that biofilm formation plays in the corrosion of copper in groundwater environment is very difficult to predict even under controlled laboratory conditions.

Free boundary approach for the attachment in the initial phase of multispecies biofilm growth

In this work, a free boundary problem is presented for the attachment process in the initial phase of multispecies biofilm formation. The free boundary is represented by the biofilm thickness and it is assumed to be initially zero. The growth of attached species is governed by nonlinear hyperbolic PDEs. The free boundary evolution is governed by a first-order differential equation depending on the attachment, detachment, biomass velocity and substrates. The quasi-static diffusion of substrates is modelled by a system of semi-linear elliptic PDEs. The qualitative analysis of solutions leads to prove existence, uniqueness and some properties of solutions. We highlight that the free boundary velocity is greater than the characteristic velocity during the first instants of biofilm formation and the free boundary is a space-like line. It is proved that the attachment function depends linearly on the concentrations of all the attaching species. The first phase of biofilm growth is shown to be completely determined by environmental conditions and characterized by a specific mathematical inequality. The opposite inequality describes the further phase where the bulk liquid stops to directly affect the biofilm life. The mentioned inequalities could be assumed as rigorous definitions of non-mature and mature biofilms, respectively.

Validation of biofilm formation on human skin wound models and demonstration of clinically translatable bacteria-specific volatile signatures

Biofilms are major contributors to delayed wound healing and there is a need for clinically relevant experimental models to assess theranostics. Microorganisms release volatile organic compounds (VOCs) and the ability to identify these in infected cutaneous wounds could lead to efficient non-invasive diagnosis. The aims here were to develop and assess bacterial biofilm formation and identify their VOC profiles in an in vitro model and validate in human ex vivo incisional and excisional cutaneous wound models. Biofilm development was assessed using multiple microscopy techniques with biofilm-forming deficient controls and quantified using metabolic and biomass assays; and VOC production measured by gas chromatography-mass spectrometry. The production of most VOCs was affected by biofilm development and model used. Some VOCs were specific either for planktonic or biofilm growth. The relative abundance of some VOCs was significantly increased or decreased by biofilm growth phase (P < 0.05). Some Staphylococcus aureus and Pseudomonas aeruginosa VOCs correlated with biofilm metabolic activity and biomass (R ≤ −0.5; ≥0.5). We present for the first time bacterial biofilm formation in human ex vivo cutaneous wound models and their specific VOC profiles. These models provide a vehicle for human skin-relevant biofilm studies and VOC detection has potential clinical translatability in efficient non-invasive diagnosis of wound infection.

Differences in survival, virulence and biofilm formation between sialidase-deficient and W83 wild-type Porphyromonas gingivalis strains under stressful environmental conditions

BackgroundPorphyromonas gingivalis is a major causative pathogen of chronic periodontitis. Within the inflammatory microenvironment, there exists extreme pH values, elevated temperatures and oxidative stress. Pathogens adapt to these stressful environmental conditions by regulating the transcription of virulence genes, modifying themselves with macromolecules and by aggregating and entering into a biofilm growth phase. Our previous study showed that the P. gingivalis sialidase can help cells obtain sialic acid from the environment, which is used to modify macromolecules on the surface of P. gingivalis cells. In this study, we compared the survival, virulence factors and biofilm formation of a sialidase-deficient strain (ΔPG0352) and the wild-type P. gingivalis W83 strain under various pH values, temperatures and oxidative stress conditions to identify the roles of sialidase in the adaptation of P. gingivalis to stressful conditions.ResultsCompared to the growth of the P. gingivalis W83 strain, the growth of the △PG0352 was more inhibited by oxidative stress (0.25 and 0.5 mM H2O2) and exhibited greater cell structure damage when treated with H2O2 as assessed by transmission electron microscopy. Both Lys-gingipain (Kgp) and Arg-gingipain (Rgp) activities were lower in the ΔPG0352 than those in the P. gingivalis W83 strain under all the assayed culture conditions. The lipopolysaccharide (LPS) activity of the W83 strain was higher than that of the ΔPG0352 under acidic conditions (pH 5.0), but no differences between the strains were observed under other conditions. Compared to the biofilms formed by P. gingivalis W83, those formed by the ΔPG0352 were decreased and discontinuous under acidic, alkaline and oxidative stress conditions.ConclusionCompared to the P. gingivalis W83 strain, the survival, virulence and biofilm formation of the ΔPG0352 were decreased under stressful environmental conditions.

Electrochemical Real-Time Analysis of Bacterial Biofilm Adhesion and Development by Means of Thin-Film Biosensors

Bacterial biofilms led to numerous problems in a wide variety of sectors as the medical environment, the food and water industry, or the naval sector. Completely developed biofilms are nearly impossible to eliminate due to the high antibiotic resistance these complex systems present. The lack of evidential indicators of their presence at the first stages of development makes antimicrobial treatments late and inadequate. Therefore, it is necessary to find new methods for the early detection of biofilm development in order to improve the efficiency of treatments by exposing bacterial cells before encapsulation in the extracellular matrix. For this purpose, this paper presents a real-time analysis of bacterial adhesion and biofilm growth by means of electrochemical measurements. Cyclic voltammetry and differential pulse voltammetry were performed with thin-film interdigitated microelectrode-based sensors. More sensitive and selective measurements were obtained with the second technique. Bacterial adhesion was detected 1 h after the initial inoculum, and three different redox centers were identified on bacterial surfaces. Finally, bacterial biofilm growth phases (lag, exponential, and stationary) were identified through the electrochemical measurements.

Phosphorus removal coupled to bioenergy production by three cyanobacterial isolates in a biofilm dynamic growth system

ABSTRACT In the present study a closed incubator, designed for biofilm growth on artificial substrata, was used to grow three isolates of biofilm-forming heterocytous cyanobacteria using an artificial wastewater secondary effluent as the culture medium. We evaluated biofilm efficiency in removing phosphorus, by simulating biofilm-based tertiary wastewater treatment and coupled this process with biodiesel production from the developed biomass. The three strains were able to grow in the synthetic medium and remove phosphorus in percentages, between 6 and 43%, which varied between strains and also among each strain according to the biofilm growth phase. Calothrix sp. biofilm turned out to be a good candidate for tertiary treatment, showing phosphorus reducing capacity (during the exponential biofilm growth) at the regulatory level for the treated effluent water being discharged into natural water systems.Besides phosphorus removal, the three cyanobacterial biofilms produced high quality lipids, whose profile showed promising chemical stability and combustion behavior. Further integration of the proposed processes could include the integration of oil extracted from these cyanobacterial biofilms with microalgal oil known for high monounsaturated fatty acids content, in order to enhance biodiesel cold flow characteristics.

Biofilm microbial community structure in an urban lake utilizing reclaimed water

Analyses of biofilm community structure may potentially be employed for aquatic ecosystem health assessment, however, to date, biofilm diversity within urban lakes using reclaimed water has not been examined. Accordingly, the microbial community diversity and structure of biofilms from the surface of multiple matrices with varying roughness (0.1, 1.0 and 10.0 μm) were characterized using a suite of molecular techniques including scanning electron microscopy, genetic fingerprinting and phospholipid-derived fatty acid analyses. Samples were largely comprised of inorganic particles, algae and numerous bacterial species; 12 phospholipid-derived fatty acid (PLFA) types were identified, significantly less than typically associated with sewage. Both growth matrix surface roughness and biofilm growth phase were shown to concur with significantly different microbial quantity and community structures. Gram-negative bacteria bacillus i15:03OH and 18:0 were the dominant bacterial genera, collectively comprising ≈75 % of identified PLFA species content. Calculated species diversity (H) and species dominance (D) exhibited identical correlational patterns with measured water quality parameters; significant positive correlations were exhibited with respect to Mg2, while significant negative correlations were found for NO3, TP, BOD, COD, SP, PO4, SO4 and pH. Results indicate that analyses of biofilm formation and structure could be effectively used to undertake integrated assessments of the ecological health of lake systems using reclaimed water. Further work is required to elucidate the optimum conditions for sample collection and analytical interpretation.

Involvement of quorum sensing genes in biofilm development and degradation of polycyclic aromatic hydrocarbons by a marine bacterium Pseudomonas aeruginosa N6P6.

Biofilm-forming and acyl homoserine lactone (AHL) synthase-positive Pseudomonas aeruginosa N6P6 was isolated from seawater after selective enrichment with two polycyclic aromatic hydrocarbons (PAHs), viz. phenanthrene and pyrene. AHL synthesis was detected qualitatively using bioreporter strains. This marine bacterium putatively synthesized N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone, which were identified by TLC, GC-MS, and HPLC. Two quorum sensing (QS) genes coding for AHL synthase, i.e., lasI and rhlI, were identified in the bacterium. lasI and rhlI gene expression was studied during biofilm mode of growth at different phases using quantitative real-time PCR (qRT-PCR). The expression of lasI increased with increase in biofilm growth. In contrast, the expression of rhlI decreased during log phase of biofilm growth. The changes in lasI/rhlI expression level had significant effects (P<0.05) on biofilm architecture and subsequent PAH degradation rate. Degradation of phenanthrene and pyrene by P. aeruginosa N6P6 was affected by biofilm growth and lasI expression. The respective phenanthrene degradation for 15, 24, 48, and 72 h old biofilm after 7 days was 21.5, 54.2, 85.6, and 85.7%. However, the corresponding pyrene degradation was 15, 18.28, 47.56, and 46.48%, respectively, after 7 days. A significant positive correlation (P<0.05) was observed between lasI expression and PAHs degradation. However, in the presence of tannic acid, a QS inhibitor (QSI), PAHs degradation, biofilm formation, and pyocyanin production reduced significantly which confirmed the pivotal role of QS in biodegradation of PAHs. The findings suggest that AHLs play a pivotal role during biofilm development and subsequent bioremediation of PAHs.

A multi-disciplinarily designed mesocosm to address the complex flow-sediment-ecology tripartite relationship on the microscale

AbstractBackgroundThe stabilization of fine sediments via biofilms (‘biostabilization’) has various economic and ecological implications but is presently unaddressed within lotic waters. To investigate natural biofilm growth and functionality in freshwater sediments under controlled boundary conditions, a unique mesocosm was constructed that combines established know-how from engineering and natural sciences and consists of six straight flumes. To test the comparability of biofilm growth within one flume and between the flumes, extracellular polymeric substances (EPSs), microbial biomass and microbial community composition were closely monitored over time and space as well as in relation to biofilm adhesiveness (proxy for biostabilization).ResultsMost importantly, biofilm development and biostabilization capacity revealed no significant differences within flume regions or between the flumes and the biofilms significantly stabilized the substratum as compared to abiotic controls. However, interesting temporal successions in biofilm growth phases became visible in shifting abundance and diversity of bacteria and microalgae resulting in varying EPS secretion and biostabilization.ConclusionsThese findings demonstrated the importance of biostabilization for fine sediment dynamics in freshwaters. Secondly, this unique setup allows comparable biofilm growth under controlled environmental conditions, an important requisite for future research on the ecological significance and impact of biostabilization for ecosystem functioning at varying environmental scenarios.

Identification of appropriate reference genes for qPCR studies in Staphylococcus pseudintermedius and preliminary assessment of icaA gene expression in biofilm-embedded bacteria.

BackgroundQuantitative PCR is rapidly becoming the standard method for analyzing gene expression in a wide variety of biological samples however it can suffer from significant error if stably expressed reference genes are not identified on which to base the analysis. Suitable reference genes for qPCR experiments on Staphylococcus pseudintermedius have yet to be identified.ResultsThree reference genes in S. pseudintermedius were identified and validated from a set of eight potential genes (proC, gyrB, rplD, rho, rpoA, ftsZ, recA, sodA). Two strains of S. pseudintermedius were used, and primer specificity and efficiency were confirmed and measured. Ranking of the genes with respect to expression stability revealed gyrB, rho and recA as the best reference genes. This combination was used to quantify expression of a single biofilm associated gene, icaA, in logarithmic, stationary and biofilm growth phases, revealing that expression was significantly upregulated in the biofilm growth phase in both strains.ConclusionThree reference genes, gyrB, rho and recA, were identified and validated for use as reference genes for quantitative PCR experiments in S. pseudintermedius. Also, the biofilm associated gene icaA was shown to be significantly upregulated in biofilm samples, consistent with its role in biofilm production.

Modelling epilithic biofilms combining hydrodynamics, invertebrate grazing and algal traits

Summary This model of stream epilithic biofilm biomass dynamics is based on the system of equations from Uehlinger et al. () and the term for autogenic detachment of biofilm from Boulêtreau et al. (). Its new features are (i) a mathematical term based on estimated feeding activity of biofilm‐dwelling invertebrates, (ii) local hydrodynamics considered as the principal factor governing algal traits and biofilm structure and (iii) a variable degree of parameterisation that was adjusted to biofilm biomass conditions. Biofilm biomass was monitored over a one‐year period in the Garonne river in France (September 2008–2009). An allometric approach was used to estimate the feeding activity of biofilm‐dwelling invertebrates based on their energetic requirements. Diatom functional diversity was also monitored to find how it varied with overall biofilm growth patterns. The one‐year monitoring period was divided into six biofilm biomass cycles, with each cycle consisting of a phase of biofilm growth as the main process, followed by detachment. This model reproduced the observed data as a complex of biofilm growth/detachment cycles using different sets of empirical parameters which allowed (i) the dominant processes involved in each biofilm cycle to be evaluated and (ii) the six cycles of biofilm growth/detachment to be reproduced. This accounted for the observed patterns more effectively than a parameterisation using a single set of empirical parameters. High flow had a severe effect on biofilm dynamics through chronic and catastrophic detachment. Presumably as a result, assemblages of diatoms shifted towards species that were firmly attached and protected by mucilage. During low flow (and when temperature was high), biofilm dynamics was mainly affected by autogenic detachment and grazer activity. The grazing pressure of the dominant biofilm‐dwelling invertebrates (Nematoda and larvae of Chironomidae and Trichoptera) was fairly low (a maximum of 6% of biofilm biomass ingested daily); nevertheless, their presence in the biofilm seemed to favour biofilm autogenic detachment.

Sequential resuspension of biofilm components (viruses, prokaryotes and protists) as measured by erodimetry experiments in the Brouage mudflat (French Atlantic coast)

Resuspension thresholds in terms of friction velocity were experimentally quantified for the prokaryotes, protists and for the first time, viruses of intertidal mudflat biofilms. Differences in resuspension thresholds could be related to the type, behaviour and size of microorganisms and their association with particles. Free microorganisms (viruses, bacteria and some nanoflagellates) were resuspended by weak flow at friction velocities lower than 2cms−1. Chlorophyll a, some nanoflagellates and attached bacteria were resuspended together with the bed's muddy sediment, which required friction velocities larger than 3cms−1. Diatoms smaller than 60μm were resuspended at velocities between 3 and 5cms−1, while those larger than 60μm were resuspended at higher friction velocities (5.5 to 6.5cms−1).The thresholds of resuspension also depended on the micro-scale position of microorganisms in the sediment (horizontal and vertical distributions). In the field, the vertical distribution of chlorophyll a (a proxy of microphytobenthos) was skewed, with a maximum in the first 2mm of sediment. Along the neap–spring tidal cycle, chlorophyll a revealed an increase in MPB biomass in the first 2mm of the sediment, in relation to light increases with exposure durations. The horizontal distribution of chlorophyll a could be inferred from erosion experiments. During the initial phase of biofilm growth, the distribution of chlorophyll a seemed horizontally homogeneous, and was uniformly eroded at the beginning of the increase in chlorophyll a. From these results, we can make a hypothesis: in the subsequent phase of biofilm growth until the maximum of emersion duration, the eroded quantity of chlorophyll a was larger than expected based from chlorophyll a vertical distribution, suggesting that biofilm horizontal distribution became patchy and enriched chlorophyll a was preferentially eroded. When emersion duration and biofilm growth decreased, the trend was reversed, and eroded quantity of chlorophyll a was lower than expected from chlorophyll a vertical distribution, suggesting that areas with low chlorophyll a were preferentially eroded. Such erosion patterns when biofilm growth decreased probably resulted from the bulldozing activity of a surficial sediment bioturbator, the gastropod Peringia ulvae. Our study did not directly prove this horizontal distribution but it should be further discussed. This distribution needs to be studied to acquire real evidence of patchy distributions.

Efficacy of Care Solutions Against Contact Lens-Associated Fusarium Biofilms

The aim of this study is to assess the effect of lens wear on the formation of soft contact lens-associated Fusarium biofilms and to determine the efficacy of marketed contact lens care products against such biofilms. Using an established in vitro soft contact lens-Fusarium biofilm model, two clinical Fusarium isolates (F. solani B6914 and F. oxysporum B8996) were incubated with three different types (lotrafilcon A, etafilcon A, and balafilcon A) of worn contact lenses under conditions that facilitate biofilm formation. Unworn lenses were used as internal controls for biofilm formation. Biofilm was quantified using a tetrazolium XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) assay. In addition, susceptibilities of the fungal biofilm growth phases to the five most common multipurpose contact lens care solutions available at the time of study (three polymeric biguanide-preserved and two polyquaternium-preserved) and two hydrogen peroxide care solutions were assessed. Both Fusarium strains formed dense biofilms on each of the contact lens types tested. Worn lenses showed no differences in the ability of biofilm to form compared with unworn lenses except worn etafilcon A lenses which formed more biofilm with F. oxyspourm B8996 compared with unworn controls. Lens material did not influence biofilm formation. The biofilms of F. solani on all three lens types were consistently susceptible to both hydrogen peroxide care systems (growth reduction of 84 to 97%, p ≤ 0.001) and two of the five multipurpose solutions (MPSs) (growth reduction of 62 to 85% for a biguanide-preserved MPS, p ≤ 0.05; growth reduction of 92 to 96% for a polyquaternium-myristamidopropyl dimethylamine preserved MPS, p < 0.001). The biofilms of F. oxysporum on all three lens types were consistently susceptible to both hydrogen peroxide care systems (growth reduction of 79 to 99%, p ≤ 0.001) and one of the five MPSs (growth reduction of 93 to 96% for a polyquaternium-myristamidopropyl dimethylamine preserved MPS, p ≤ 0.001). F. solani and F. oxysporum form biofilms on lotrafilcon A, etafilcon A, and balafilcon A worn contact lenses, which are resistant to the antifungal activity of several soft contact lens care products. Only the hydrogen peroxide care systems and one polyquaternium-myristamidopropyl dimethylamine-preserved solution consistently demonstrated effective antifungal activity against both Fusarium strains on all three lens types.