Biofilm Thickness Research Articles

Biofilm analyses and exoproduct release by clinical and environmental isolates of Burkholderia pseudomallei from Brazil

Objective: To characterize biofilm production by clinical (n=21) and environmental (n=11) isolates of Burkholderia pseudomallei and evaluate the production of proteases, hemolysins and siderophores. Methods: Initially, the 32 strains were evaluated for biofilm production in Müller-Hinton broth-1% glucose (MH-1% glucose) and BHI broth-1% glucose, using the crystal violet staining technique. Subsequently, growing (48 h) and mature (72 h) biofilms were evaluated by confocal microscopy. Finally, the production of proteases, hemolysins and siderophores by planktonic aggregates, growing biofilms and mature biofilms was evaluated. Results: All isolates produced biofilms, but clinical isolates had significantly higher biomass in both MH-1% glucose (P<0.001) and BHI-glucose 1% (P=0.005). The structural analyses by confocal microscopy showed thick biofilms, composed of multiple layers of cells, homogeneously arranged, with mature biofilms of clinical isolates presenting higher biomass (P=0.019) and thickness of the entire area (P=0.029), and lower roughness coefficient (P=0.007) than those of environmental isolates. Protease production by growing biofilms was significantly greater than that of planktonic (P<0.001) and mature biofilms (P<0.001). Hemolysin release by planktonic aggregates was higher than that of biofilms (P<0.001). Regarding siderophores, mature biofilms presented higher production than growing biofilms (P<0.001) and planktonic aggregates (P<0.001). Conclusions: Clinical isolates have higher production of biofilms than their environmental counterparts; protease and siderophores seem important for growth and maintenance of Burkholderia pseudomallei biofilms.

Biofilm Reactor with Permeable Materials as Carriers Archives Better and More Stable Performance in Treatment of Slightly Polluted Water during Long-Term Operation

Biofilms in reactors usually grow on impermeable surfaces, and the mass transfer of nutrients in biofilms is mainly driven by diffusion, which is inefficient especially for thick biofilms. In this study, permeable materials (i.e., nylon meshes) were used as biocarriers in a biofilm reactor, and their performance was evaluated and compared with the commercial biocarriers (PE08 and PE10) used for treating slightly polluted water. The results indicate that the mesh-based bioreactor achieved complete nitrification faster than the commercial biocarriers, with a more stable and better effluent quality during long-term operation. At a two-hour hydraulic retention time, the average effluent ammonia (NH4+-N) and nitrite (NO2−-N) concentrations during the stabilized phase were 0.97 ± 0.79 and 0.61 ± 0.32 mg-N, respectively, which are significantly lower than those with commercial carriers. The estimated specific surface area activities for the mesh, PE08, and PE10 carriers were 1620, 769, and 1300 mg-N/(m2·d)), respectively. The biofilms formed on the nylon mesh were porous, while they were compact and nonporous on the PE carriers. Water with substrates might pass through the porous biofilms formed on the meshes, which could enhance mass transfer and result in a better and more stable treatment performance.

Activity of Ammonium-Oxidizing Bacteria—An Essential Parameter for Model-Based N2O Mitigation Control Strategies for Biofilms

The reduction in N2O emissions is an important task in the control of wastewater treatment plants. Since local operating conditions, especially inside biofilms, are usually not known, models are an important tool in the development and implementation of control strategies. For a pilot-scale nitrifying biofilm reactor and an SBR, different operational strategies to reduce autotrophic nitrous oxide (N2O) formation were developed and tested by applying a combination of modeling and measurement. Both approaches highlighted the relevance of addressing the actual AOB activity as a sensitive control variable. The investigated strategies, therefore, focused on decreasing the AOB-related NH4 conversion rate, as autotrophic N2O formation is directly linked to AOB activity. The results showed that the biofilm system was more advantageous compared with suspended sludge systems. A higher AOB content resulted in a decrease in AOB activity, leading to fewer N2O emissions at the same reactor performance. The highest reduction in autotrophic N2O formation (SBR: 25%; Biofilm: 27%) was obtained by maximizing the aerated time per day and minimizing the number of aeration cycles (the suppression of nitrite-oxidizing bacteria still needed to be ensured). A higher biofilm thickness or a higher sludge mass in the SBR, however, did not have a noteworthy positive effect since no additional biomass could be kept in the system in the long term due to limited substrate availability. Besides nitritation, denitrification was also identified as a relevant source of N2O in both systems (biofilm: main source) due to the inhibition of N2O reduction by nitrous acid (elevated nitrite concentrations in combination with pH values < 7).

Mono and bilayer coatings of alkanethiol and silane on copper: Prevents corrosion and regulate bacterial adhesion

Self-assembling molecules (SAMs) provide a flexible system for surface modification of materials by forming films of molecular thickness. SAMs protect materials from corrosion and modify surface properties such as adhesion, adsorption and wetting due to their molecular composition and orientation. In this investigation, polished copper specimens were dip coated to form SAMs of alkanethiol and silane to study bacterial adhesion as well as for corrosion prevention. The SAM coated specimens were exposed to the log phase cultures of Pseudomonas aeruginosa (aerobic bacteria) and Desulfovibrio vulgaris (anaerobic bacteria) for 12, 24 and 48 hrs, to monitor cell adhesion and biofilm thickness by microscopy. The results showed that alkanethiols SAM promoted adhesion and biofilm formation. The biofilm thickness ranged from 10 to 38 µm for Pseudomonas and 9 – 25 µm for Desulfovibrio sp. Among the SAM coatings tested, octadecyl-trichlorosilane (ODTCS), alkane-thiol and ODTCS (bilayer SAM) showed no bacterial adhesion, however, solitary alkane-thiol SAM showed significant bacterial adhesion. The high hydrophobicity (contact angle ∼140°), antibacterial and anti-biofilm property of the ODTCS coating could have regulated bacterial adhesion. The constant climate test results showed that silane SAM prevented copper corrosion up to ∼160 days (3480 hrs), while the alkanethiol coating could protect up to 10 days (240 hrs). Confocal laser scanning microscopic images of the silane coated copper specimens showed initiation of the corrosion after 160 days of exposure, while at the end of 200 days significant copper corrosion was observed. Surface modification leads to specific biochemical interactions that regulate bacterial adhesion and prevent biofilm formation and corrosion of copper.

Natural biopatina on historical petroglyphs in the Austrian Alps: To clean or not to clean?

Some of Austria's most important petroglyphs are located in the alpine region of Dachstein, carved in the local limestone. Favored by the humid and shady environment, most of the engravings are covered by extensive biological colonization. In order to assess whether and to what extent the biopatinas present on the stone cause biodeterioration, we investigated their interactions with the rock substrate by microscopy methods (and PAS-staining), in combination with a metagenomic analysis to identify the biofilms' composition. The microscopy methods highlighted a general biodeterioration state of the stone and the great boring ability of the biofilms, especially of those with filamentous cyanobacteria (e.g., Nostocales and Oscillatoriales), and showed that a thick moss biofilm (with high abundance of Bacteroidota taxa) was the most harmful for the stone support, causing severe disruption of the underlying rock. Interestingly, the analysis of stone without visible biofilm revealed a microbiome dominated by ammonia-oxidizing archaea (AOAs), probably indicating the presence of a previous degraded biofilm (source of ammonia), and a current state of deterioration (dissolution of calcium carbonate). Removal of the biopatinas, or their alteration, would expose an already altered surface, potentially giving rise to a new colonization and new cycles of biodeterioration.

Cell surface hydrophobicity and petroleum hydrocarbon degradation by biofilm-forming marine bacterium Pseudomonas furukawaii PPS-19 under different physicochemical stressors

Biofilm-forming marine bacterium Pseudomonas furukawaii PPS-19 showed strong hydrophobicity under different physicochemical stressors, such as pH and salinity. Strong aggregation of P. furukawaii PPS-19 was observed at hydrophobic interfaces of n-dodecane and crude oil, while uptake of pyrene resulted in blue fluorescence of the bacterium. Changes in biofilm microcolonies were observed under different physicochemical stressors with maximum biofilm thickness of 15.15 µm and 15.77 µm at pH 7% and 1% salinity, respectively. Relative expression analysis of alkB2 gene revealed the maximum expression in n-dodecane (10.5 fold) at pH 7 (1 fold) and 1% salinity (8.3 fold). During the degradation process, a significant drop in surface tension resulted in increased emulsification activity. P. furukawaii PPS-19 showed the respective n-dodecane and pyrene degradation of 94.3% and 81.5% at pH 7% and 94.5% and 83% at 1% salinity. A significant positive correlation was obtained between cell surface hydrophobicity (CSH), biofilm formation, and PHs degradation (P < 0.05) under all the physicochemical stressors, with the highest value at pH 7% and 1% salinity. Analysis of metabolites indicated that mono-terminal oxidation and multiple pathways were followed for n-dodecane and pyrene biodegradation, respectively. Thus, P. furukawaii PPS-19 is an efficient hydrocarbonoclastic bacterium that may be exploited for large-scale oil pollution abatement.

Characterization of functional amyloid curli in biofilm formation of an environmental isolate Enterobacter cloacae SBP-8.

The biofilm formation by bacteria is a complex process that is strongly mediated by various genetic and environmental factors. Biofilms contribute to disease infestation, especially in chronic infections. It is, therefore important to understand the factors affecting biofilm formation. This study reports the role of a functional amyloid curli in biofilm formation at various abiotic surfaces, including medical devices, by an environmental isolate of Enterobacter cloacae (SBP-8) which has been known for its pathogenic potential. A knockout mutant of csgA, the gene encoding the major structural unit of curli, was created to study the effect of curli on biofilm formation by E. cloacae SBP-8. Our findings confirm the production of curli at 25°C and 37°C in the wild-type strain. We further investigated the role of curli in the attachment of E. cloacae SBP-8 to glass, enteral feeding tube, and foley latex catheter. Contrary to the previous studies reporting the curli production below 30°C in the majority of biofilm-forming bacterial species, we observed its production in E. cloacae SBP-8 at 37°C. The formation of more intense biofilm in wild-type strain on various surfaces compared to curli-deficient strain (ΔcsgA) at both 25°C and 37°C suggested a prominent role of curli in biofilm formation. Further, electron and confocal microscopy studies demonstrated the formation of diffused monolayers of microbial cells on the abiotic surfaces by ΔcsgA strain as compared to the thick biofilm by respective wild-type strain, indicating the involvement of curli in biofilm formation by E. cloacae SBP-8. Overall, our findings provide insight into biofilm formation mediated by curli in E. cloacae SBP-8. Further, we show that it can be expressed at a physiological temperature on all surfaces, thereby indicating the potential role of curli in pathogenesis.

Risk factor-based clustering of Listeria monocytogenes in food processing environments using principal component analysis

Listeria monocytogenes has a range of strategies that allow it to persist as biofilms in food processing environments (FPE), making it a pathogen of concern to the food industry. The properties of these biofilms are highly variable among strains, and this significantly affects the risk of food contamination. The present study therefore aims to conduct a proof-of-concept study to cluster strains of L. monocytogenes by risk potential using principal component analysis, a multivariate approach.A set of 22 strains, isolated from food processing environments, were typed by serogrouping and pulsed-field gel electrophoresis, showing a relatively high diversity. They were characterized in terms of several biofilm properties that might pose a potential risk of food contamination. The properties studied were tolerance to benzalkonium chloride (BAC), the structural parameters of biofilms (biomass, surface area, maximum and average thickness, surface to biovolume ratio and roughness coefficient) measured by confocal laser scanning microscopy and (3) transfer of biofilm cells to smoked salmon.The PCA correlation circle revealed that the tolerance of biofilms to BAC was positively correlated with roughness, but negatively with biomass parameters. On the contrary, cell transfers were not related to three-dimensional structural parameters, which suggests the role of other variables yet unexplored. Additionally, hierarchical clustering grouped strains into three different clusters. One of them included the strains with high tolerance to BAC and roughness. Another one consisted of strains with enhanced transfer ability, whereas the third cluster contained those that stood out for the thickness of biofilms. The present study represents a novel and effective way to classify L. monocytogenes strains according to biofilm properties that condition the potential risk of reaching the consumer through food contamination. It would thus allow the selection of strains representative of different worst-case scenarios for future studies in support of QMRA and decision-making analysis.

Long-term operation and biofouling of graphene oxide membrane in practical water treatment: Insights from performance and biofilm characteristics

The widespread research of graphene oxide (GO) membranes has revealed the need to investigate their long-term performance and associated biofouling behavior in practical water treatment conditions. In this study, we have evaluated the long-term operation of GO membranes from the perspective of filtration performance and biofilm characteristics, based on two representative GO membranes (V-GO and P-GO, fabricated by vacuum and pressure filtration, respectively) with different surface properties and a natural surface water, using a gravity driven membrane system. The results showed that the GO membranes were capable of achieving sustainable water purification over 45 days of operation, associated with a complete rejection for biopolymers and desirable removal for fluorescent organic matters. Furthermore, the V-GO membrane with a rougher surface, reduced hydrophilicity and higher sheet-edge exposure than that of the P-GO membrane formed a highly heterogeneous and porous biofilm with high permeability, despite its greater biofilm thickness and extracellular polymeric substances (EPS) contents. In contrast, the P-GO membrane biofilm exhibited a thin but dense structure, and therefore an increased hydraulic resistance (∼1.5 times greater than V-GO membrane). The microbial community analysis revealed that bacteria related to biofilm formation was richer in V-GO biofilm. While bacteria associated with the degradation of organic matters and the aggregation of microorganisms accounted for a greater proportion in P-GO biofilm. These factors were responsible for forming a thick biofilm for V-GO, and a thin but high resistance biofilm for P-GO membrane. Our findings highlight the sustainable water purification performance of the GO membranes, and the P-GO membrane can alleviate biofilm formation but not necessarily reduce biofouling during the long-term filtration, while this was opposite in case of the V-GO membrane.

A gravity-driven membrane bioreactor in treating the real decentralized domestic wastewater: Flux stability and membrane fouling

Domestic wastewater in decentralized sites is capturing increasing attention. However, conventional treatment technology is not sufficiently cost-effective. In this study, real domestic wastewater was treated directly using a gravity-driven membrane bioreactor (GDMBR) at 45 mbar without backwashing or chemical cleaning, and the effects of different membrane pore sizes (0.22 μm, 0.45 μm, and 150 kDa) on flux development and contaminants removal were examined. The results showed that the flux initially decreased and then stabilized throughout long-term filtration and that the stabilized flux level of the GDMBR equipped the membranes with the pore size of 150 kDa and 0.22 μm was higher than that of 0.45 μm membrane and was in the range of 3–4 L m−2h−1. The flux stability was related to spongelike and permeable biofilm generation on the membrane surface in the GDMBR system. The presence of aeration shear on the membrane surface would cause the slough off of biofilm from the membrane surface, especially in the scenarios of GDMBR with the membrane pore size of 150 kDa and 0.22 μm, contributing to lower accumulation of extracellular polymeric substance (EPS) and smaller biofilm thickness compared to that of 0.45 μm membrane. Furthermore, the GDMBR system achieved efficient removals of chemical oxygen demand (COD), and ammonia, with average removal efficiencies of 60–80% and 70%. The high biological activity and microbial community diversity within the biofilm would improve its biodegradation and should be responsible for the efficient removal performance of contaminants. Interestingly, the membrane effluent could effectively retain total nitrogen (TN) and total phosphorus (TP). Therefore, it's feasible to adopt the GDMBR process to treat the actual domestic wastewater in the decentralized locations, and these findings could be expected to develop some simple and environmentally friendly strategies for decentralized wastewater treatment with fewer inputs.

P-021 DELAYED ENTEROCUTANEOUS FISTULA AND ENCAPSULATING MESH INFECTION AFTER COMPOSITE MESH REPAIR OF AN ABDOMINAL MIDLINE INCISIONAL HERNIA - COMPLICATIONS 12 YEARS LATER

Abstract Aim Mesh infection is a well-recognised complication of incisional hernia repair, however, is usually encountered within months after mesh insertion. Only a few cases have been published where an enterocutaneous fistula has presented many years after mesh repair of an incisional hernia. Here we describe a complicated case of enterocutaneous fistula and mesh infection 12 years after the primary surgery. Material &amp; Methods A 44 year-old gentleman presented acutely with a worsening 4 month history of an umbilical discharging sinus with associated fever, intermittent abdominal pain and nausea. There was also an associated hard lump and skin erythema. He previously had a laparotomy, small bowel resection for tuberculosis and ileostomy formation 13 years ago, followed by ileostomy reversal and intraperitoneal incisional hernia repair with composite mesh 1 year later. Results Cross-sectional imaging showed a large volume of gas within the mesh with underlying small bowel and collection within anterior abdominal wall, suggesting an enterocutaneous fistula. The patient initially underwent ultrasound guided aspiration of the collection followed by nutritional optimisation prior to another laparotomy, mesh excision and small bowel resection. The mesh was found to have a thick biofilm initially thought to be encased in mycobacterium but further testing was negative for this. Conclusions Delayed mesh infection over more than a decade after mesh insertion is rare. It is likely that pre-existing risk factors such as previous TB and small bowel resection with adhesions increased the risk of enterocutaneous fistulation.

Relationships between composite roughness and Streptococcus mutans biofilm depth under shear in vitro

ObjectiveTo investigate the effect of substrate, surface roughness, and hydraulic residence time (HRT) on Streptococcus mutans biofilms growing on dental composites under conditions relevant to the oral cavity. MethodsDental composites were prepared with varying amounts of polishing and incubated in a CDC bioreactor with an approximate shear of 0.4 Pa. S. mutans biofilms developed in the bioreactors fed sucrose or glucose and at 10-h or 40-h HRT for one week. Biofilms were characterized by confocal laser microscopy (CLM). Composite surface roughness was characterized by optical profilometry, and pre- and post-incubation composite surface fine structure and elemental composition were determined using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). ResultsPolishing had a significant impact on surface roughness, varying by a factor of 15 between the polished samples and the unpolished control. S. mutans biofilms grew statistically significantly thicker on the unpolished composites. Biofilm thickness was greater at shorter 10-h HRT compared to 40-h HRT. In most cases, biofilm thickness was not statistically significantly greater in sucrose-fed bioreactors than in glucose-fed bioreactors. SEM-EDS analysis did not identify any significant change in elemental composition after aging. ConclusionsAccurate characterization of oral cavity biofilms must consider shear forces and the use of techniques that minimize alteration of the biofilm structure. Under shear, surface smoothness is the most important factor determining S. mutans biofilm thickness followed by HRT, while sucrose presence did not result in significantly greater biofilm thickness. Clinical SignificanceThe obvious patterns of S. mutans growth along sub-micron scale grooving created by the polishing process suggested that initial biofilm attachment occurred in the shear-protected grooves. These results suggest that fine polishing may help prevent the initial formation of S. mutans biofilms compared to unpolished/coarse polished composites.

Impact of anthropogenic sounds (pile driving, drilling and vessels) on the development of model species involved in marine biofouling

The uncontrolled colonization of benthic organisms on submerged surfaces, also called biofouling, causes severe damage in the shipping and aquaculture industries. Biofouling starts with a benthic biofilm composed of a complex assemblage of microbes, bacteria and benthic diatoms, called microfouling, on which macrofouling invertebrate species settle and grow. Invertebrate larvae may use natural soundscapes to orientate inshore and choose their optimal habitat. Recent studies have demonstrated that ship sounds enhance the larval settlement and growth of several invertebrate species, such as mussels, associated with biofouling. Among invertebrates, effects of sound generated by offshore human activities are still poorly studied. This study aims to assess the effect of pile driving, drilling and vessel sounds on model species associated with micro and macrofouling. First, the biofilm development of Navicula pelliculosa and Amphora coffeaeformis was assessed, then, the larval development of the blue mussel (Mytilus edulis) was evaluated from the D-veliger to the postlarval stage. Mussel larvae and microalgae were exposed 12 h each day in tanks (Larvosonic) adapted to sound experiments under controlled conditions. All anthropogenic sounds induced a thinner N. pelliculosa biofilm coupled with a lower microalgae concentration. The drilling sound had a stronger effect on the biofilm thickness. The drilling sound significantly reduced the pediveliger settlement and the postlarvae clearance rate by 70.4% and tended to diminish settler sizes compared to control sound. Contrary to our expectation, pile driving tended to enhance larval recruitment by 22% (P=0.077) and the boat sound did not stimulate larval settlements or recruitment. Drilling sound generated a stressful acoustic environment for pediveliger settlements and postlarvae seem to maintain their shell valves closed to preserve energy. We identify potential causes and mechanisms involved in these impacts of anthropophony on larval ecology and microfouling dynamics.

Membranolytic Activity Profile of Nonyl 3,4-Dihydroxybenzoate: A New Anti-Biofilm Compound for the Treatment of Dermatophytosis.

The ability of dermatophytes to live in communities and resist antifungal drugs may explain treatment recurrence, especially in onychomycosis. Therefore, new molecules with reduced toxicity that target dermatophyte biofilms should be investigated. This study evaluated nonyl 3,4-dihydroxybenzoate (nonyl) susceptibility and mechanism of action on planktonic cells and biofilms of T. rubrum and T. mentagrophytes. Metabolic activities, ergosterol, and reactive oxygen species (ROS) were quantified, and the expression of genes encoding ergosterol was determined by real-time PCR. The effects on the biofilm structure were visualized using confocal electron microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). T. rubrum and T. mentagrophytes biofilms were susceptible to nonyl and resistant to fluconazole, griseofulvin (all strains), and terbinafine (two strains). The SEM results revealed that nonyl groups seriously damaged the biofilms, whereas synthetic drugs caused little or no damage and, in some cases, stimulated the development of resistance structures. Confocal microscopy showed a drastic reduction in biofilm thickness, and transmission electron microscopy results indicated that the compound promoted the derangement and formation of pores in the plasma membrane. Biochemical and molecular assays indicated that fungal membrane ergosterol is a nonyl target. These findings show that nonyl 3,4-dihydroxybenzoate is a promising antifungal compound.

Kurstakin Triggers Multicellular Behaviors in Bacillus cereus AR156 and Enhances Disease Control Efficacy Against Rice Sheath Blight.

Kurstakin is the latest discovered family of lipopeptides secreted by Bacillus spp. In this study, the effects of kurstakin on the direct antagonism, multicellularity, and disease control ability of Bacillus cereus AR156 were explored. An insertion mutation in the nonribosomal peptide synthase responsible for kurstakin synthesis led to a significant reduction of antagonistic ability of AR156 against the plant-pathogenic fungi Rhizoctonia solani, Ascochyta citrullina, Fusarium graminearum, and F. oxysporum f. sp. cubense. The loss of kurstakin synthesis ability significantly impaired the swarming motility of AR156 and reduced biofilm formation and amyloid protein accumulation. Although the loss of kurstakin synthesis ability did not reduce the competitiveness of AR156 under laboratory conditions, the colonization and environmental adaptability of the mutant was significantly weaker than that of wild-type AR156 on rice leaves. The cell surface of wild-type AR156 colonizing the leaf surface was covered by a thick biofilm matrix under a scanning electron microscope, but not the mutant. The colonization ability on rice roots and control efficacy against rice sheath blight disease of the mutant were also impaired. Thus, kurstakin participates in the control of plant diseases by B. cereus AR156 through directly inhibiting the growth of pathogenic fungi and improving long-term environmental adaptability and colonization of AR156 on the host surface by triggering multicellularity. This study explored the multiple functions of kurstakin in plant disease control by B. cereus.

Modeling Co-Infection by Streptococcus suis and Haemophilus parasuis Reveals Influences on Biofilm Formation and Host Response.

Streptococcus suis (S. suis) and Haemophilus parasuis (H. parasuis) are two primary pathogens currently affecting the porcine industry. They often cause encephalitis and arthritis. They also frequently co-infect in clinical settings. In the current study, we identified significant correlations between S. suis and H. parasuis. The results from CI versus RIR suggested that S. suis and H. parasuis were competitive in general. Compared to mono-species biofilm, the biomass, bio-volume, and thickness of mixed-species biofilms were significantly higher, which was confirmed using crystal violet staining, confocal laser scanning microscopy, and scanning electron microscopy. Compared to mono-species biofilm, the viable bacteria in the mixed-species biofilms were significantly lower, which was confirmed using the enumeration of colony-forming units (CFU cm-2). The susceptibility of antibiotics in the co-culture decreased in the planktonic state. In contrast, biofilm state bacteria are significantly more difficult to eradicate with antibiotics than in a planktonic state. Whether in planktonic or biofilm state, the expression of virulence genes of S. suis and H. parasuis in mixed culture was very different from that in single culture. Subsequently, by establishing a mixed infection model in mice, we found that the colonization of the two pathogens in organs increased after mixed infection, and altered the host's inflammatory response. In summary, our results indicate that S. suis and H. parasuis compete when co-cultured in vitro. Surprisingly, S. suis and H. parasuis synergistically increased colonization capacity after co-infection in vivo. This study elucidated the interaction between S. suis and H. parasuis during single infections and co-infections. Future studies on bacterial disease control and antibiotic treatment should consider the interaction of mixed species.

Carbon dots internalization enhances electroactive biofilm formation and microbial acetate synthesis

This study investigated how carbon dots (CDs) and N-doped CDs modification of acetogenic bacteria enhanced the extracellular electron transfer (EET) and the formation of electroactive biofilm, which subsequently improved acetate production from CO2 in microbial electrosynthesis (MES). Characteristic fluorescence emission peaks of CDs and N-doped CDs were detected inside and outside of bacterial cells, respectively, suggesting that the CDs were successfully internalized by the cells. The (N-doped) CDs modified acetogens increased current output by 89–95%, and acetate production rate by 57–71%. The highest acetate production rate and electron recovery efficiency reached 2.1 mM d−1 and 91.3%, respectively. Acetoanaerobium and Sporomusa, which are considered to have different EET strategies, dominated the biocathodes modified with CDs and N-doped CDs, respectively. The CDs modification increased biofilm thickness by 86% and reached 41.0 ± 1.3 μm, which could be related to the increased secretion of flavins that enhanced the signal transduction interspecies. With the N-doped CDs modified, the biofilm was occupied with active pyrrolic N/graphitic N (52%), and the expression of functional genes encoding cytochrome (cydB, cybH, CcdA) were enhanced significantly. This study offers insights into the EET mechanisms by acetogens and a viable approach to increase acetate production from CO2.

Combined Application of Antisense Oligomers to Control Transcription Factors of Candida albicans Biofilm Formation.

Antisense oligomers (ASOs) have been little exploited to control determinants ofCandida albicansvirulence. Biofilm formation is an important virulence factor of C. albicans, that is regulated by a complex network of transcription factors (such as EFG1, BRG1 and ROB1). Thus, the main goal of this work was to project ASOs, based on the 2'-OMethyl chemical modification, to targetBRG1andROB1mRNA and to validate its application either alone or in combination with the EFG1 mRNA target, to reduceC. albicans biofilm formation. The ability of ASOs to control gene expression was evaluate by qRT-PCR. The effect on biofilm formation was determined by the total biomass quantification, and simultaneously the carbohydrates and proteins reduction on extracellular matrix. It was verified that all the oligomers were able to reduce the levels of gene expression and the ability of C. albicans to form biofilms. Furthermore, the combined application of the cocktail of ASOs enhances the inhibition of C. albicans biofilm formation, minimizing biofilm thickness by reducing the quantity of matrix content (protein and carbohydrate). So, our work confirms that ASOs are useful tools for research and therapeutic development on the control of Candida species biofilm formation.

Antibacterial, antibiofilm, and anti-quorum sensing activities of pyocyanin against methicillin-resistant Staphylococcus aureus: in vitro and in vivo study

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) infections are considered a major public health problem, as the treatment options are restricted. Biofilm formation and the quorum sensing (QS) system play a pivotal role in S. aureus pathogenicity. Hence, this study was performed to explore the antibacterial effect of pyocyanin (PCN) on MRSA as well as its effect on MRSA biofilm and QS.ResultsData revealed that PCN exhibited strong antibacterial activity against all test MRSA isolates (n = 30) with a MIC value equal to 8 µg/ml. About 88% of MRSA biofilms were eradicated by PCN treatment using the crystal violet assay. The disruption of MRSA biofilm was confirmed using confocal laser scanning microscopy, which showed a reduction in bacterial viability (approximately equal to 82%) and biofilm thickness (approximately equal to 60%). Additionally, the disruption of the formation of microcolonies and the disturbance of the connection between bacterial cells in the MRSA biofilm after PCN treatment were examined by scanning electron microscopy. The 1/2 and 1/4 MICs of PCN exerted promising anti-QS activity without affecting bacterial viability; Agr QS-dependent virulence factors (hemolysin, protease, and motility), and the expression of agrA gene, decreased after PCN treatment. The in silico analysis confirmed the binding of PCN to the AgrA protein active site, which blocked its action. The in vivo study using the rat wound infection model confirmed the ability of PCN to modulate the biofilm and QS of MRSA isolates.ConclusionThe extracted PCN seems to be a good candidate for treating MRSA infection through biofilm eradication and Agr QS inhibition.

Lignocellulose reconstituted shape-controllable self-supporting carbonaceous capacitance-anodes with high electron transfer rates for high-performance microbial electrochemical system

Natural biomass is a promising candidate for manufacturing an efficient anode in the microbial electrochemical system (MES) for its abundance and low cost. However, the structure and performance of the electrode highly depend on the biomass species. A simple and sustainable method for creating a self-supporting electrode is proposed by freeze-drying and carbonizing a blend of cellulose, lignin, and hemicellulose. This strategy leads to a cork-like structure and improved mechanical strength of the lignocellulose carbon. A power density of 4780 ± 260 mW m−2 (CLX-800) was achieved, which was the highest record for unmodified lignocellulose-based anodes in the microbial fuel cells. The morphological as lamellar multilayer and rich in hydrophilic functional groups could facilitate the formation of thick electroactive biofilms and enrich Geobacter with the highest abundance of 92.3%. The CLX material is expected to be the ideal electrode for high performance and functionally controllability.