Dual roles of the conditional extracellular vesicles derived from Pseudomonas aeruginosa biofilms: Promoting and inhibiting bacterial biofilm growth

Antibiotic-resistant biofilm infections have emerged as public health concerns because of their enhanced tolerance to high-dose antibiotic treatments. The biofilm life cycle involves multiple developmental stages, which are tightly regulated by active cell-cell communication via specific extracellular signal messengers such as extracellular vesicles. This study was aimed at exploring the roles of extracellular vesicles secreted by Pseudomonas aeruginosa at different developmental stages in controlling biofilm growth. Our results show that extracellular vesicles secreted by P. aeruginosa biofilms during their exponential growth phase (G-EVs) enhance biofilm growth. In contrast, extracellular vesicles secreted by P. aeruginosa biofilms during their death/survival phase (D-EVs) can effectively inhibit/eliminate P. aeruginosa PAO1 biofilms up to 4.8-log10 CFU/cm2. The inhibition effectiveness of D-EVs against P. aeruginosa biofilms grown for 96 h improved further in the presence of 10-50 μM Fe3+ ions. Proteomic analysis suggests the inhibition involves an iron-dependent ferroptosis mechanism. This study is the first to report the functional role of bacterial extracellular vesicles in bacterial growth, which depends on the developmental stage of the parent bacteria. The finding of D-EV-activated ferroptosis-based bacterial death may have significant implications for preventing antibiotic resistance in biofilms.

Evaluation of Treatment of Methicillin-Resistant Staphylococcus aureus Biofilms with Intermittent Electrochemically-Generated H2O2 or HOCl

Chronic wound infections can be difficult to treat and may lead to impaired healing and worsened patient outcomes. Novel treatment strategies are needed. This study evaluated effects of intermittently produced H2O2 and HOCl, generated via an electrochemical bandage (e-bandage), against methicillin-resistant Staphylococcus aureus biofilms in an agar membrane biofilm model. By changing the working electrode potential, the e-bandage generated either HOCl (1.5 VAg/AgCl) or H2O2 (-0.6 VAg/AgCl). The degree of biocidal activity of intermittent treatment with HOCl and H2O2 correlated with HOCl treatment time; HOCl treatment durations of 0, 1.5, 3, 4.5, and 6 hours (with the rest of the 6 hour total treatment time devoted to H2O2 generation) resulted in mean biofilm reductions of 1.36±0.2, 2.22±0.16, 3.46±0.38, 4.63±0.74 and 7.66±0.5 log CFU/cm2, respectively vs. non-polarized controls, respectively. However, application of H2O2 immediately after HOCl treatment was detrimental to biofilm removal. For example, 3-hours HOCl treatment followed by 3-hours H2O2 resulted in a 1.90±0.84 log CFU/cm2 lower mean biofilm reduction than 3-hours HOCl treatment followed by 3-hours non-polarization. HOCl generated over 3-hours exhibited biocidal activity for at least 7.5-hours after e-bandage operation ceased; 3-hours of HOCl generation followed by 7.5-hours of non-polarization resulted in a biofilm cell reduction of 7.92±0.12 log CFU/cm2 vs. non polarized controls. Finally, intermittent treatment with HOCl (i.e., interspersed with periods of e-bandage non-polarization) for various intervals showed similar effects (approximately 6 log CFU/cm2 reduction vs. non-polarized control) to continuous treatment with HOCl for 3-hours, followed by 3-hours of non-polarization. These findings suggest that timing and sequencing of HOCl and H2O2 treatments are crucial for maximizing biofilm control.

DUAL ACTION ELECTROCHEMICAL BANDAGE OPERATED by a PROGRAMMABLE MULTIMODAL WEARABLE POTENTIOSTAT

Electrochemical bandages (e-bandages) can be applied to biofilm-infected wounds to generate reactive oxygen species, such as hypochlorous acid (HOCl) or hydrogen peroxide (H 2 O 2 ). The e-bandage-generated HOCl or H 2 O 2 kills biofilms in vitro and in infected wounds on mice. The HOCl-generating e-bandage is more active against biofilms in vitro , although this distinction is less apparent in vivo . The H 2 O 2 -generating e-bandage, more than the HOCl-generating e-bandage, is associated with improved healing of infected wounds. A strategy in which H 2 O 2 and HOCl are generated alternately-for dual action-was explored. The goal was to develop a programmable multimodal wearable potentiostat (PMWP) that could be programmed to generate HOCl or H 2 O 2 , as needed. An ultralow-power microcontroller unit managed operation of the PMWP. The system was operated with a 260-mAh capacity coin battery and weighed 4.6 grams, making it suitable for small animal experiments or human use. The overall cost of a single wearable potentiostat was $6.50 (USD). The device was verified using established electrochemical systems and functioned comparably to a commercial potentiostat. To determine antimicrobial effectiveness, PMWP-controlled e-bandages were tested against clinical isolates of four prevalent chronic wound bacterial pathogens, methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter baumannii , and Enterococcus faecium , and one fungal pathogen of emerging concern, Candida auris . PMWP-controlled e-bandages exhibited broad-spectrum activity against biofilms of all study isolates tested when programmed to deliver HOCl followed by H 2 O 2 . These results show that the PMWP operates effectively and is suitable for animal testing.

HOCl-producing Electrochemical Bandage is Active in Murine Polymicrobial Wound Infection

Wound infections, exacerbated by the prevalence of antibiotic-resistant bacterial pathogens, necessitate innovative antimicrobial approaches. Polymicrobial infections, often involving Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), present formidable challenges due to biofilm formation and antibiotic resistance. Hypochlorous acid (HOCl), a potent antimicrobial agent produced naturally by the immune system, holds promise as an alternative therapy. An electrochemical bandage (e-bandage) that generates HOCl in situ was evaluated for treatment of murine wound biofilm infections containing both MRSA and P. aeruginosa with "difficult-to-treat" resistance. Previously, the HOCl-producing e-bandage was shown to reduce wound biofilms containing P. aeruginosa alone. Compared to non-polarized e-bandage (no HOCl production) and Tegaderm only controls, the polarized e-bandages reduced bacterial loads in wounds infected with MRSA plus P. aeruginosa (MRSA: vs Tegaderm only - 1.4 log10 CFU/g, p = 0.0015, vs. non-polarized - 1.1 log10 CFU/g, p = 0.026. P. aeruginosa: vs Tegaderm only - 1.6 log10 CFU/g, p = 0.0015, vs non-polarized - 1.6 log10 CFU/g, p = 0.0032), and MRSA alone (vs Tegaderm only - 1.3 log10 CFU/g, p = 0.0048, vs. non-polarized - 1.1 log10 CFU/g, p = 0.0048), without compromising wound healing or causing tissue toxicity. Addition of systemic antibiotics did not enhance the antimicrobial efficacy of e-bandages, highlighting their potential as standalone therapies. This study provides additional evidence for the HOCl-producing e-bandage as a novel antimicrobial strategy for managing wound infections, including in the context of antibiotic resistance and polymicrobial infections.

A Response Surface Methodology Study for Chlorella vulgaris Mixotrophic Culture Optimization

Glycerol is a carbon source that produces good biomass under mixotrophic conditions. Enhancing the composition of culture media in algae biomass production improves growth rates, biomass yield, nutrient utilization efficiency, and overall cost-effectiveness. Among the key nutrients in the medium, nitrogen plays a pivotal role. Urea can be effectively used as a nitrogen source and is considered a low-cost form of nitrogen compared to other sources. Urea metabolism releases some CO2 in photosynthesis, and magnesium plays a major role in urea uptake. Magnesium is another key nutrient that is key in photosynthesis and other metabolic reactions. To maximize glycerol consumption in the mixotrophic system and to obtain high biomass and lipid productions, the variations in MgSO4·7H2O and urea concentrations were evaluated in the growth medium of the microalgae. A response surface methodology (RSM) using a central composite design (CCD) was designed to maximize glycerol consumption at the initial cellular growth rates (up to four days). The magnesium and urea supply varied from 0.3 to 1.7 g L-1. Response surface methodology was utilized to analyze the results, and the highest glycerol consumption rate, 770.2 mg L-1 d-1, was observed when C. vulgaris was grown at 1.7 g L-1 urea, 1.0 g L-1 MgSO4·7H2O. Using the optimal urea and magnesium concentrations with acetate, glucose, and glycerol as carbon sources, the same lipid content (10% average) was achieved on day 4 of mixotrophic C. vulgaris culture. Overall, the results show that mixotrophic growth of C. vulgaris using urea with an optimum magnesium concentration yields large amounts of fatty acids and that the carbon source greatly influences the profile of the fatty acids.

HOCl-producing electrochemical bandage for treating Pseudomonas aeruginosa-infected murine wounds

The growing threat of antibiotic-resistant bacterial pathogens necessitates the development of alternative antimicrobial approaches. This is particularly true for chronic wound infections, which commonly harbor biofilm-dwelling bacteria. A novel electrochemical bandage (e-bandage) delivering low-levels of hypochlorous acid (HOCl) was evaluated against Pseudomonas aeruginosa murine wound biofilms. 5 mm skin wounds were created on the dorsum of mice and infected with 106 colony-forming units (CFU) of P. aeruginosa. Biofilms were formed over 2 days, after which e-bandages were placed on the wound beds and covered with Tegaderm. Mice were administered Tegaderm-only (control), non-polarized e-bandage (no HOCl production), or polarized e-bandage (using an HOCl-producing potentiostat), with or without systemic amikacin. Purulence and wound areas were measured before and after treatment. After 48 hours, wounds were harvested for bacterial quantification. Forty-eight hours of polarized e-bandage treatment resulted in mean biofilm reductions of 1.4 log10 CFUs/g (P = 0.0107) vs non-polarized controls and 2.2 log10 CFU/g (P = 0.004) vs Tegaderm-only controls. Amikacin improved CFU reduction in Tegaderm-only (P = 0.0045) and non-polarized control groups (P = 0.0312) but not in the polarized group (P = 0.3876). Compared to the Tegaderm-only group, there was less purulence in the polarized group (P = 0.009). Wound closure was neither impeded nor improved by either polarized or non-polarized e-bandage treatment. Concurrent amikacin did not impact wound closure or purulence. In conclusion, an HOCl-producing e-bandage reduced P. aeruginosa in wound biofilms with no impairment in wound healing, representing a promising antibiotic-free approach for addressing wound infection.

HOCl-producing Electrochemical Bandages for Treating Pseudomonas aeruginosa -Infected Murine Wounds

A novel electrochemical bandage (e-bandage) delivering low-level hypochlorous acid (HOCl) was evaluated against Pseudomonas aeruginosa murine wound biofilms. 5 mm skin wounds were created on the dorsum of Swiss-Webster mice and infected with 10 6 colony forming units (CFU) of P. aeruginosa . Biofilms were formed over two days, after which e-bandages were placed on the wound beds and covered with Tegaderm™. Mice were administered Tegaderm-only (control), non-polarized e-bandage (no HOCl production), or polarized e-bandage (using an HOCl-producing potentiostat), with or without concurrently administered systemic amikacin. Purulence and wound areas were measured before and after treatment. After 48 hours, animals were sacrificed, and wounds were harvested for bacterial quantification. Forty-eight hours of polarized e-bandage treatment resulted in mean biofilm reductions of 1.4 log 10 CFUs/g (9.0 vs 7.6 log 10 ; p = 0.0107) vs non-polarized controls, and 2.2 log 10 CFU/g (9.8 vs 7.6 log 10 ; p = 0.004) vs Tegaderm only controls. Systemic amikacin improved CFU reduction in Tegaderm-only (p = 0.0045) and non-polarized control groups (p = 0.0312), but not in the polarized group (p = 0.3876). Compared to the Tegaderm only group, there was more purulence reduction in the polarized group (p = 0.009), but not in the non-polarized group (p = 0.064). Wound closure was not impeded or improved by either polarized or non-polarized e-bandage treatment. Concurrent amikacin did not impact wound closure or purulence. In conclusion, an HOCl-producing e-bandage reduced P. aeruginosa in wound biofilms with no impairment in wound healing, representing a promising antibiotic-free approach for addressing wound infections.

In vitro activity of hypochlorous acid generating electrochemical bandage against monospecies and dual-species bacterial biofilms

AIMS

As antimicrobial resistance is on the rise, treating chronic wound infections is becoming more complex. The presence of biofilms in wound beds contributes to this challenge. Here, the activity of a novel hypochlorous acid (HOCl) producing electrochemical bandage (e-bandage) against monospecies and dual-species bacterial biofilms formed by bacteria commonly found in wound infections was assessed.

METHODS AND RESULTS

The system was controlled by a wearable potentiostat powered by a 3V lithium-ion battery and maintaining a constant voltage of + 1.5V Ag/AgCl, allowing continuous generation of HOCl. A total of 19 monospecies and 10 dual-species bacterial biofilms grown on polycarbonate membranes placed on tryptic soy agar (TSA) plates were used as wound biofilm models, with HOCl producing e-bandages placed over the biofilms. Viable cell counts were quantified after e-bandages were continuously polarized for 2, 4, 6, and 12 hours. Time-dependent reductions in colony forming units (CFUs) were observed for all studied isolates. After 12 hours, average CFU reductions of 7.75 ± 1.37 and 7.74 ± 0.60 log10 CFU/cm2 were observed for monospecies and dual-species biofilms, respectively.

CONCLUSIONS

HOCl producing e-bandages reduce viable cell counts of in vitro monospecies and dual-species bacterial biofilms in a time-dependent manner in vitro. After 12 hours, >99.999% reduction in cell viability was observed for both monospecies and dual-species biofilms.

In Vivo Activity of Hydrogen‐Peroxide Generating Electrochemical Bandage Against Murine Wound Infections

Biofilms formed by antibiotic-resistant bacteria in wound beds present unique challenges in terms of treating wound infections. In this work, the in vivo activity of a novel electrochemical bandage (e-bandage) composed of carbon fabric and controlled by a wearable potentiostat, designed to continuously deliver low amounts of hydrogen peroxide (H₂O₂) was evaluated against methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Pseudomonas aeruginosa (MDR-PA) and mixed-species (MRSA and MDR-PA) wound infections. Wounds created on Swiss Webster mice were infected with the above-named bacteria and biofilms allowed to establish on wound beds for 3 days. e-Bandages, which electrochemically reduce dissolved oxygen to H₂O₂ when polarized at -0.6 V_Ag/AgCl, were placed atop the infected wound bed and polarized continuously for 48 hours. Polarized e-bandage treatment resulted in significant reductions (p <0.001) of both mono-species and mixed-species wound infections. After e-bandage treatment, electron microscopy showed degradation of bacterial cells, and histopathology showed no obvious alteration to the inflammatory host response. Blood biochemistries showed no abnormalities. Taken all together, results of this work suggest that the described H₂O₂-producing e-bandage can effectively reduce in vivo MRSA, MDR-PA and mixed-species wound biofilms, and should be further developed as a potential antibiotic-free strategy for treatment of wound infections.

Activity of a hypochlorous acid-producing electrochemical bandage as assessed with a porcine explant biofilm model

The activity of a hypochlorous acid-producing electrochemical bandage (e-bandage) in preventing methicillin-resistant Staphylococcus aureus infection (MRSA) infection and removing biofilms formed by MRSA was assessed using a porcine explant biofilm model. e-Bandages inhibited S. aureus infection (p = 0.029) after 12 h (h) of exposure and reduced 3-day biofilm viable cell counts after 6, 12, and 24 h exposures (p = 0.029). Needle-type microelectrodes were used to assess HOCl concentrations in explant tissue as a result of e-bandage treatment; toxicity associated with e-bandage treatment was evaluated. HOCl concentrations in infected and uninfected explant tissue varied between 30 and 80 µM, decreasing with increasing distance from the e-bandage. Eukaryotic cell viability was reduced by an average of 71% and 65% in fresh and day 3-old explants, respectively, when compared to explants exposed to nonpolarized e-bandages. HOCl e-bandages are a promising technology that can be further developed as an antibiotic-free treatment for wound biofilm infections.

Anti-Biofilm Activity of a Tunable Hypochlorous Acid-Generating Electrochemical Bandage Controlled By a Wearable Potentiostat

Chronic wound biofilm infections represent a major clinical challenge which results in a substantial burden to patients and healthcare systems. Treatment with topical antibiotics is oftentimes ineffective as a result of antibiotic-resistant microorganisms and biofilm-specific antibiotic tolerance. Use of biocides such as hypochlorous acid (HOCl) has gained increasing attention due to the lack of known resistance mechanisms. We designed an HOCl-generating electrochemical bandage (e-bandage) that delivers HOCl continuously at low concentrations targeting infected wound beds in a similar manner to adhesive antimicrobial wound dressings. We developed a battery-operated wearable potentiostat that controls the e-bandage electrodes at potentials suitable for HOCl generation. We demonstrated that e-bandage treatment was tunable by changing the applied potential. HOCl generation on electrode surfaces was verified using microelectrodes. The developed e-bandage showed time-dependent responses against in vitro Acinetobacter baumannii and Staphylococcus aureus biofilms, reducing viable cells to non-detectable levels within 6 and 12 hours of treatment, respectively. The developed e-bandage should be further evaluated as an alternative to topical antibiotics to treat wound biofilm infections.

Hypochlorous acid produced at the counter electrode inhibits catalase and increases bactericidal activity of a hydrogen peroxide generating electrochemical bandage

Previously, an electrochemical bandage (e-bandage) that uses a three-electrode system to produce hydrogen peroxide (H2O2) electrochemically on its working electrode was developed as a potential strategy for treating biofilms; it showed activity in reducing biofilms in an agar biofilm model. Xanthan gum-based hydrogel, including NaCl, was used as the electrolyte. While H2O2 generated at the working electrode in the vicinity of a biofilm is a main mechanism of activity, the role of the counter electrode was not explored. The goal of this research was to characterize electrochemical reactions occurring on the counter electrode of the e-bandage. Counter electrode potential varied between 1.2 and 1.5 VAg/AgCl; ∼125 µM hypochlorous acid (HOCl) was generated within 24 h in the e-bandage system. When HOCl was not produced on the counter electrode (achieved by removing NaCl from the hydrogel), reduction of Acinetobacter baumannii BAA-1605 biofilm was 1.08 ± 0.38 log10 CFU/cm2 after 24 h treatment, whereas when HOCl was produced, reduction was 3.87 ± 1.44 log10 CFU/cm2. HOCl inhibited catalase activity, abrogating H2O2 decomposition. In addition to H2O2 generation, the previously described H2O2-generating e-bandage generates HOCl on the counter electrode, enhancing its biocidal activity.

Efficacy and toxicity of hydrogen peroxide producing electrochemical bandages in a porcine explant biofilm model

AIMS

Effects of H₂ O₂ producing electrochemical-bandages (e-bandages) on methicillin-resistant Staphylococcus aureus colonization and biofilm removal were assessed using a porcine explant biofilm model. Transport of H₂ O₂ produced from the e-bandage into explant tissue and associated potential toxicity were evaluated.

METHODS AND RESULTS

Viable prokaryotic cells from infected explants were quantified after 48 h treatment with e-bandages in three ex vivo S. aureus infection models: (1) reducing colonization, (2) removing young biofilms and (3) removing mature biofilms. H₂ O₂ concentration-depth profiles in explants/biofilms were measured using microelectrodes. Reductions in eukaryotic cell viability of polarized and nonpolarized noninfected explants were compared. e-Bandages effectively reduced S. aureus colonization (p = 0.029) and reduced the viable prokaryotic cell concentrations of young biofilms (p = 0.029) with limited effects on mature biofilms (p > 0.1). H₂ O₂ penetrated biofilms and explants and reduced eukaryotic cell viability by 32-44% compared to nonpolarized explants.

CONCLUSIONS

H₂ O₂ producing e-bandages were most active when used to reduce colonization and remove young biofilms rather than to remove mature biofilms.

SIGNIFICANCE AND IMPACT OF STUDY

The described e-bandages reduced S. aureus colonization and young S. aureus biofilms in a porcine explant wound model, supporting their further development as an antibiotic-free alternative for managing biofilm infections.

Investigating microbial dynamics and potential advantages of anaerobic co-digestion of cheese whey and poultry slaughterhouse wastewaters

Resource recovery and prevention of environmental pollution are key goals for sustainable development. It is widely reported that agro-industrial activities are responsible for the discharge of billions of liters of wastewater to the environment. Anaerobic digestion of these energy rich agro-industrial wastewaters can simultaneously mitigate environmental pollution and recover embedded energy as methane gas. In this study, an assessment of mono- and co-digestion of cheese whey wastewater (CWW) and poultry slaughterhouse wastewater (PSW) was conducted in 2.25-L lab-scale anaerobic digesters. Treatment combinations evaluated included CWW (R1), PSW (R2), 75:25 CWW:PSW (R3), 25:75 CWW:PSW (R4), and 50:50 CWW:PSW (R5). The digestion efficiencies of the mixed wastewaters were compared to the weighted efficiencies of the corresponding combined mono-digested samples. R4, with a mixture of 25% CWW and 75% PSW, achieved the greatest treatment efficiency. This corresponded with an average biodegradability of 84%, which was greater than for R1 and R2 at 68.5 and 71.9%, respectively. Similarly, R4 produced the highest average cumulative methane value compared to R1 and R2 at 1.22× and 1.39× for similar COD loading, respectively. The modified Gompertz model provided the best fit for the obtained methane production data, with lag time decreasing over progressive treatment cycles. PCoA and heatmap analysis of relative microbial abundances indicated a divergence of microbial communities based on feed type over the treatment cycles. Microbial community analysis showed that genus Petrimonas attained the highest relative abundance (RA) at up to 38.9% in the first two cycles, then subsequently decreased to near 0% for all reactors. Syntrophomonas was highly abundant in PSW reactors, reaching up to 36% RA. Acinetobacter was present mostly in CWW reactors with a RA reaching 56.5%. The methanogenic community was dominated by Methanothrix (84.3–99.9% of archaea). The presence of phosphate and Acinetobacter in CWW feed appeared to reduce the treatment efficiency of associated reactors. Despite Acinetobacter being strictly aerobic, previous and current results indicate its survival under anaerobic conditions, with the storage of phosphate likely playing a key role in its ability to scavenge acetate during the digestion process.

Rapid differentiation of antibiotic-susceptible and -resistant bacteria through mediated extracellular electron transfer

Conventional methods for testing antibiotic susceptibility rely on bacterial growth on agar plates (diffusion assays) or in liquid culture (microdilution assays). These time-consuming assays use population growth as a proxy for cellular respiration. Herein we propose to use mediated extracellular electron transfer as a rapid and direct method to classify antibiotic-susceptible and -resistant bacteria. We tested antibiotics with diverse mechanisms of action (ciprofloxacin, imipenem, oxacillin, or tobramycin) with four important nosocomial pathogens (Acinetobacter baumannii, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae) by adding the bacterial culture to a custom-designed electrochemical cell with a glassy-carbon electrode and growth media supplemented with a soluble electron transfer mediator, phenazine methosulfate (PMS). During cell respiration, liberated electrons reduce PMS, which is then oxidized on the electrode surface, and current is recorded. Using this novel approach, we were able to consistently classify strains as antibiotic-resistant or -susceptible in <90 min for methodology development and <150 min for blinded tests.

Exosomes as Powerful Engines in Cancer: Isolation, Characterization and Detection Techniques

Exosomes, powerful extracellular nanovesicles released from almost all types of living cells, are considered the communication engines (messengers) that control and reprogram physiological pathways inside target cells within a community or between different communities. The cell-like structure of these extracellular vesicles provides a protective environment for their proteins and DNA/RNA cargos, which serve as biomarkers for many malicious diseases, including infectious diseases and cancers. Cancer-derived exosomes control cancer metastasis, prognosis, and development. In addition to the unique structure of exosomes, their nanometer size and tendency of interacting with cells makes them a viable novel drug delivery solution. In recent years, numerous research efforts have been made to quantify and characterize disease-derived exosomes for diagnosis, monitoring, and therapeutic purposes. This review aims to (1) relate exosome biomarkers to their origins, (2) focus on current isolation and detection methods, (3) discuss and evaluate the proposed technologies deriving from exosome research for cancer treatment, and (4) form a conclusion about the prospects of the current exosome research.

773. Hypochlorous Acid Generating Electrochemical Catheter Prototype for Prevention of Intraluminal Infections

Background

Central-line associated bloodstream infection (CLABSI) contributes to mortality and cost. While aseptic dressings and antibiotic-impregnated catheters can prevent extraluminal infections, intraluminal infections remain a source of CLABSIs with limited prevention options.

Methods

In this proof-of-concept study, an electrochemical intravascular catheter (e-catheter) prototype capable of electrochemically generating hypochlorous acid intraluminally on the surface of platinum electrodes polarized at a constant potential of 1.5 VAg/AgCl was developed. After 24h of pre-polarization at 1.5 VAg/AgCl, their activity was tested by inoculating four clinical isolates derived from catheter-related infections, Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecium and Escherichia coli.

Figure 1. In vitro catheter and e-catheter models.

Results

E-catheters generated a mean HOCl concentration of 15.86±4.03 μM and had a mean pH of 6.14±0.79. e-catheters prevented infections with all four species, with an average reduction of 8.41±0.61 log10 CFU/mL at 48h compared to controls.

Figure 3. Measurement of pH and HOCl at 48 hours in polarized e-catheters.

Each dot represents a replicate; bars represent means.

Figure 4. Prevention of infection after 48 hours of polarization (24 hours of infections) using e-catheters (polarized and non-polarized) compared to blank catheters.

* indicates statistically significant reduction of cell counts in polarized e-catheter compared to blank catheter (p <0.05).

Conclusion

Polarized e-catheters which generate low amounts of HOCl continuously should be further developed to prevent intraluminal infection.

Disclosures

Haluk Beyenal, Ph.D, patent (Other Financial or Material Support, HB holds a patent: Beyenal H CD, Fransson BA, Sultana ST. . 2018. Electrochemical reduction or prevention of infections. U.S. patent 20180207301A1, international patent WO/2017/011635.) Robin Patel, MD, 1928 Diagnostics (Consultant)BioFire Diagnostics (Grant/Research Support)ContraFect Corporation (Grant/Research Support)Curetis (Consultant)Hylomorph AG (Grant/Research Support)IDSA (Other Financial or Material Support, Editor's Stipend)Infectious Diseases Board Review Course (Other Financial or Material Support, Honoraria)Mammoth Biosciences (Consultant)NBME (Other Financial or Material Support, Honoraria)Netflix (Consultant)Next Gen Diagnostics (Consultant)PathoQuest (Consultant)PhAST (Consultant)Qvella (Consultant)Samsung (Other Financial or Material Support, Patent Royalties)Selux Diagnostics (Consultant)Shionogi & Co., Ltd. (Grant/Research Support)Specific Technologies (Consultant)TenNor Therapeutics Limited (Grant/Research Support)Torus Biosystems (Consultant)Up-to-Date (Other Financial or Material Support, Honoraria) Robin Patel, MD, BioFire (Individual(s) Involved: Self): Grant/Research Support; Contrafect (Individual(s) Involved: Self): Grant/Research Support; IDSA (Individual(s) Involved: Self): Editor's stipend; NBME, Up-to-Date and the Infectious Diseases Board Review Course (Individual(s) Involved: Self): Honoraria; Netflix (Individual(s) Involved: Self): Consultant; TenNor Therapeutics Limited (Individual(s) Involved: Self): Grant/Research Support; to Curetis, Specific Technologies, Next Gen Diagnostics, PathoQuest, Selux Diagnostics, 1928 Diagnostics, PhAST, Torus Biosystems, Mammoth Biosciences and Qvella (Individual(s) Involved: Self): Consultant

Kinetics and scale up of oxygen reducing cathodic biofilms

The goals of this work were to study the kinetics and investigate the factors controlling the scale up of oxygen reducing mixed culture cathodic biofilms. Cathodic biofilms were enriched on different electrode sizes (14.5 cm2, 40.3 cm2, 131 cm2 and 466 cm2). Biofilm enrichment shifted the oxygen reduction onset potential from -0.1 VAg/AgCl to 0.3 VAg/AgCl, indicating the biofilm catalyzed oxygen reduction. The kinetics of oxygen reduction were studied by varying the bulk dissolved oxygen concentration. Oxygen reduction followed a Michaelis-Menten kinetics on all electrode sizes. The maximum current density decreased with increasing electrode surface area (-97.0 ± 10.6 μA/cm2, -76.0 ± 8.2 μA/cm2, -66.3 ± 3.0 μA/cm2 and -43.5 ± 10.5 μA/cm2, respectively). Cyclic voltammograms suggest that scale up was limited by ohmic resistance, likely due to the low ionic conductivity in the wastewater medium. Mathematical modeling using combined Michaelis-Menten and Butler-Volmer model supports that the decrease in current density with increasing electrode surface area is caused by ohmic losses. Analysis of the microbial community structure in different size electrodes and in multiple regions on the same electrode showed low variability, suggesting that the microbial community does not control the scale up of cathodic biofilms.

Hydrogen-peroxide generating electrochemical bandage is active in vitro against mono- and dual-species biofilms

Biofilms formed by antibiotic-resistant bacteria in wound beds present unique challenges in terms of treating chronic wound infections; biofilms formed by one or more than one bacterial species are often involved. In this work, the in vitro anti-biofilm activity of a novel electrochemical bandage (e-bandage) composed of carbon fabric and controlled by a wearable potentiostat, designed to continuously deliver low amounts of hydrogen peroxide (H2O2) was evaluated against 34 mono-species and 12 dual-species membrane bacterial biofilms formed by Staphylococcus aureus, S. epidermidis, Enterococcus faecium, E. faecalis, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Cutibacterium acnes, and Bacteroides fragilis. Biofilms were grown on polycarbonate membranes placed atop agar plates. An e-bandage, which electrochemically reduces dissolved oxygen to H2O2 when polarized at -0.6 VAg/AgCl, was then placed atop each membrane biofilm and polarized continuously for 12, 24, and 48 h using a wearable potentiostat. Time-dependent decreases in viable CFU counts of all mono- and dual-species biofilms were observed after e-bandage treatment. 48 h of e-bandage treatment resulted in an average reduction of 8.17 ± 0.40 and 7.99 ± 0.32 log10 CFU/cm2 for mono- and dual-species biofilms, respectively. Results suggest that the described H2O2 producing e-bandage can reduce in vitro viable cell counts of biofilms grown either in mono- or dual-species forms, and should be further developed as a potential antibiotic-free treatment strategy for treating chronic wound infections.

Electrochemically Active Biofilms as an Indicator of Soil Health

Soil health is a complex phenomenon that reflects the ability of soil to support both plant growth and other ecosystem functions. To our knowledge, research on extracellular electron transfer processes in soil environments is limited and could provide novel knowledge and new ways of monitoring soil health. Electrochemical activities in the soil can be studied by inserting inert electrodes. Once the electrode is polarized to a favorable potential, nearby microorganisms attach to the electrodes and grow as biofilms. Biofilms are a major part of the soil and play critical roles in microbial activity and community dynamics. Our work aims to investigate the electrochemical behavior of healthy and unhealthy soils using chronoamperometry and cyclic voltammetry. We developed a bioelectrochemical soil reactor for electrochemical measurements using healthy and unhealthy soils taken from the Cook Agronomy Farm Long-Term Agroecological Research site; the soils showed similar physical and chemical characteristics, but there was higher plant growth where the healthy soil was taken. Using carbon cloth electrodes installed in these soil reactors, we explored the electrochemical signals in these two soils. First, we measured redox variations by depth and found that reducing conditions were prevalent in healthy soils. Current measurements showed distinct differences between healthy and unhealthy soils. Scanning electron microscopy images showed the presence of microbes attached to the electrode for healthy soil but not for unhealthy soil. Glucose addition stimulated current in both soil types and caused differences in cyclic voltammograms between the two soil types to converge. Our work demonstrates that we can use current as a proxy for microbial metabolic activity to distinguish healthy and unhealthy soil.

Biofilm addition improves sand strength over a wide range of saturations

Bio-mediated ground improvement is an attractive alternative to traditional admixtures for strength improvement of shallow surfaces because it is environmentally friendly. Since biofilms contain extracellular polymeric substances (EPS), they can be considered as an alternative to current technologies to improve soil strength. EPS containing biofilms are porous materials with charged surfaces, and therefore adsorption and capillary condensation can result in water retention. Currently, most of the literature work only tested soil improvement under the dry condition. Therefore, the influence of water retention by biofilms on the strength of improved soil remains unclear. Our goal is to evaluate the strength of a biofilm-enhanced sand over a wide range of saturations and explain the trends through the suction stress characteristic curve (SSCC), which quantifies interparticle adsorptive, capillary, and cementation forces as a function of saturation. We used homogenized anaerobic granule biofilms from an existing upflow anaerobic sludge blanket reactor and mixed it with sand to test the strength of a poorly-graded sand in a wide range of saturations, S (between 0.02 S and 0.74 S). We found that biofilm treatment of sand increases soil strength through cementation over a wide range of saturations and through adsorptive forces among sand, biofilm surfaces, and water molecules at low saturations (S < ~0.3). Our results suggested that homogenized biofilms mixed with sand can be used to improve the strength of sand over a wide range of saturations.

Hydrogen peroxide-producing electrochemical bandage controlled by a wearable potentiostat for treatment of wound infections

Chronic wound infections caused by biofilm-forming microorganisms represent a major burden to healthcare systems. Treatment of chronic wound infections using conventional antibiotics is often ineffective due to the presence of bacteria with acquired antibiotic resistance and biofilm-associated antibiotic tolerance. We previously developed an electrochemical scaffold that generates hydrogen peroxide (H₂ O₂ ) at low concentrations in the vicinity of biofilms. The goal of this study was to transition our electrochemical scaffold into an H₂ O₂ -generating electrochemical bandage (e-bandage) that can be used in vivo. The developed e-bandage uses a xanthan gum-based hydrogel to maintain electrolytic conductivity between e-bandage electrodes and biofilms. The e-bandage is controlled using a lightweight, battery-powered wearable potentiostat suitable for use in animal experiments. We show that e-bandage treatment reduced colony-forming units of Acinetobacter buamannii biofilms (treatment vs. control) in 12 h (7.32 ± 1.70 vs. 9.73 ± 0.09 log₁₀ [CFU/cm² ]) and 24 h (4.10 ± 12.64 vs. 9.78 ± 0.08 log₁₀ [CFU/cm² ]) treatments, with 48 h treatment reducing viable cells below the limit of detection of quantitative and broth cultures. The developed H₂ O₂ -generating e-bandage was effective against in vitro A. baumannii biofilms and should be further evaluated and developed as a potential alternative to topical antibiotic treatment of wound infections.

The effect of additional salinity on performance of a phosphate buffer saline buffered three-electrode bioelectrochemical system inoculated with wastewater

In bioelectrochemical system (BES), phosphate buffer saline (PBS) is usually used to achieve a suitable pH condition, which also increases electrolyte salinity. A series of factors that change with salinity will affect BES performance. To simplify the scenario, a three-electrode BES is used to investigate how additional salinity affects the performance of a 50 mM PBS-buffered BES. Results demonstrated that current production decreased with increasing salinity and the dominant exoelectrogens were not inhibited with the addition of 200 mM NaCl. The distribution of system resistance was analyzed by electrochemical impedance spectroscopy. Compared to the decreased solution and biofilm resistance, the increased interfacial resistance that accounted for up to 97.8% of total resistance was the dominant reason for the decreased current production with the increasing additional salinity. The effects of additional salinity on acetate degradation and columbic efficiency were also analyzed.

Large-scale switchable potentiostatically controlled/microbial fuel cell bioelectrochemical wastewater treatment system

The treatment of municipal wastewater is an energy-intensive process, with the delivery of oxygen as an electron acceptor accounting for a significant share of the total energy consumption. Microbial communities growing on polarized electrodes can facilitate wastewater treatment processes by exchanging electrons with the electrodes. As a new approach, we combined the use of polarized electrodes with microbial fuel cells (MFCs) to develop a switchable dual-mode bioelectrochemical wastewater treatment system. In this system, we first enriched microbial communities on polarized anodes and cathodes. After enrichment, the system was switched to either a self-powered MFC (SP-MFC) mode or a potentiostatically controlled (PC) mode. The system was evaluated at the laboratory scale (260 L, 4 anode and cathode pairs) and the pilot scale (1200 L, 16 anode and cathode pairs). PC and SP-MFC systems showed improved COD removal relative to control (41.6 ± 3.5 and 38.4 ± 3.1 vs 28.8 ± 2.1 mg L^-1 d^-1, respectively). The laboratory-scale system was operated without biological or electrical interruption for one year. Finally, specific enrichment of active microbial communities was observed on PC anodes in comparison to mixed-operation and non-polarized control anodes. The combined PC and SP-MFC systems allowed us to develop a sustainable and failure-free bioelectrochemical wastewater treatment system.

Growth of 'Candidatus Liberibacter asiaticus' in a host-free microbial culture is associated with microbial community composition

'Candidatus Liberibacter asiaticus' ('Ca. L. asiaticus'), the suspected causative agent of citrus greening disease, is one of many phloem-restricted plant pathogens that have not been isolated and grown in an axenic culture. In this study, infected Asian citrus psyllids were used to prepare a host-free source of 'Ca. L. asiaticus'. Host-free mixed microbial cultures of 'Ca. L. asiaticus' were grown in the presence of various antibiotic treatments to alter the composition of the microbial communities. Our hypothesis was that the presence of selected antibiotics would enhance or reduce the presence of 'Ca. L. asiaticus' in a host-free culture composed of a mixed bacterial population through changes in the microbial community structure. We determined how 'Ca. L. asiaticus' growth changed with the various treatments. Treatment with vancomycin (50 μg/mL), streptomycin (0.02 μg/mL), or polymyxin B (4 μg/mL) was associated with an increased abundance of 'Ca. L. asiaticus' of 7.35 ± 0.27, 5.56 ± 0.15, or 4.54 ± 0.83 fold, respectively, compared to untreated mixed microbial cultures, while treatment with 100 μg/mL vancomycin; 0.5, 1, or 2 μg/mL streptomycin; or 0.5 μg/mL of polymyxin B was associated with reduced growth. In addition, the growth of 'Ca. L. asiaticus' was associated with the microbial community composition of the mixed microbial cultures. A positive relationship between the presence of the Pseudomonadaceae family and 'Ca. L. asiaticus' growth was observed, while the presence of 'Ca. L. asiaticus' was below the detection limit in cultures that displayed high abundances of Bacillus cereus. Our findings offer strategies for developing effective axenic culture conditions and suggest that enrichment of the Bacillaceae family could serve as a paratransgenic approach to controlling citrus greening disease.

Biomass-derived nanocarbon materials for biological applications: challenges and prospects

Biomass-derived nanocarbons (BNCs) have attracted significant research interests due to their promising economic and environmental benefits. Following their extensive uses in physical and chemical research domains, BNCs are now growing in biological applications. However, their practical biological applications are still in their infancy, requiring critical evaluations and strategic directions, which are provided in this review. The carbonization of biomass sources and major types of BNCs are introduced, encompassing carbon nanodots, nanofibres, nanotubes, and graphenes. Next, essential biological uses of BNCs, antibacterial/antibiofilm materials (nanofibres and nanodots) and bioimaging agents (predominantly nanodots), are summarized. Furthermore, the future potential of BNCs, for designing wound dressing/healing materials, water and air disinfection platforms, and microbial electrochemical systems, is discussed. We reach the conclusion that a crucial challenge is the structural control of BNCs. Furthermore, a key knowledge gap for realizing practical biological applications is the lack of systematic comparisons of BNCs with nanocarbons of synthetic origin in the current literature. Although we did not attempt to perform an exhaustive literature survey, the evaluation of the existing results indicates that BNCs are promising as easily accessible materials for various biomedically and environmentally relevant applications.

Electrochemical precipitation of neptunium with a micro electrochemical quartz crystal microbalance

Microliter volumes are used in electrochemical detection and preconcentration of radionuclides to reduce the dose received by researchers and equipment. Unfortunately, there is a lack of analysis of radionuclides with coupled electrochemical techniques and microliter volume reactors. The goals of this work are 1) to develop a miniaturized micro-electrochemical quartz crystal microbalance (µeQCM) reactor for use in small volume (50-200 µL) electrogravimetric experiments and 2) to use this reactor to characterize the preconcentration of neptunium on carbon electrodes via electroprecipitation. We successfully deposited neptunium in the new µeQCM reactor and verified its operation. We found that preconcentration of neptunium on carbon coated electrodes was possible by chronoamperometry at -1.6 VAg/AgCl. The mass shift of the resulting precipitate was indicative of the amount of neptunium on the electrode, although the correlation between the mass increase and activity of the preconcentrated material was not linear. Neptunium precipitate reduced electron transfer to the solution as evidenced by the increase in charge transfer resistance compared to bare electrodes.

Hypochlorous acid-generating electrochemical scaffold eliminates Candida albicans biofilms

AIMS

Wound infections involving Candida albicans can be challenging to treat because of the fungus' ability to penetrate wound tissue and form biofilms. The goal of this study was to assess the activity of a hypochlorous acid (HOCl)-generating electrochemical scaffold (e-scaffold) against C. albicans biofilms in vitro and on porcine dermal explants (ex vivo).

METHODS AND RESULTS

C. albicans biofilms were grown either on acrylic-bottom six-well plates (in vitro) or on skin tissue excised from porcine ears (ex vivo), and the polarized e-scaffold was used to generate a continuous supply of low concentration HOCl near biofilm surfaces. C. albicans biofilms grown in vitro were reduced to undetectable amounts within 24 h of e-scaffold exposure, unlike control biofilms (5·28 ± 0·034 log₁₀  (CFU cm^{- 2} ); P < 0·0001). C. albicans biofilms grown on porcine dermal explants were also reduced to undetectable amounts in 24 h, unlike control explant biofilms (4·29 ± 0·057 log₁₀ (CFU cm^{- 2} ); P < 0·0001). There was a decrease in the number of viable mammalian cells (35·6 ± 6·4%) in uninfected porcine dermal explants exposed to continuous HOCl-generating e-scaffolds for 24 h compared to explants exposed to nonpolarized e-scaffolds (not generating HOCl) (P < 0·05).

CONCLUSIONS

Our HOCl-generating e-scaffold is a potential antifungal-free strategy to treat C. albicans biofilms in chronic wounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

Wound infections caused by C. albicans are difficult to treat due to presence of biofilms in wound beds. Our HOCl producing e-scaffold provides a promising novel approach to treat wound infections caused by C. albicans.

Controlled replication of 'Candidatus Liberibacter asiaticus' DNA in citrus leaf discs

'Candidatus Liberibacter asiaticus' is a fastidious bacterium and a putative agent of citrus greening disease (a.k.a., huanglongbing, HLB), a significant agricultural disease that affects citrus fruit quality and tree health. In citrus, 'Ca. L. asiaticus' is phloem limited. Lack of culture tools to study 'Ca. L. asiaticus' complicates analysis of this important organism. To improve understanding of 'Ca. L. asiaticus'-host interactions including parameters that affect 'Ca. L. asiaticus' replication, methods suitable for screening pathogen responses to physicochemical and nutritional variables are needed. We describe a leaf disc-based culture assay that allows highly selective measurement of changes in 'Ca. L. asiaticus' DNA within plant tissue incubated under specific physicochemical and nutritional conditions. qPCR analysis targeting the hypothetical gene CD16-00155 (strain A4) allowed selective quantification of 'Ca. L. asiaticus' DNA content within infected tissue. 'Ca. L. asiaticus' DNA replication was observed in response to glucose exclusively under microaerobic conditions, and the antibiotic amikacin further enhanced 'Ca. L. asiaticus' DNA replication. Metabolite profiling revealed a moderate impact of 'Ca. L. asiaticus' on the ability of leaf tissue to metabolize and respond to glucose.

Three-dimensional biofilm image reconstruction for assessing structural parameters

Parameters representing three-dimensional (3D) biofilm structure are quantified from confocal laser-scanning microscope (CLSM) images. These 3D parameters describe the distribution of biomass pixels within the space occupied by a biofilm; however, they lack a direct connection to biofilm activity. As a result, researchers choose a handful of parameters without there being a consensus on a standard set of parameters. We hypothesized that a select 3D parameter set could be used to reconstruct a biofilm image and that the reconstructed and original biofilm images would have similar activities. To test this hypothesis, an algorithm was developed to reconstruct a biofilm image with parameters identical to those of the original CLSM image. We introduced an objective method to assess the reconstruction algorithm by comparing the activities of the original and reconstructed biofilm images. We found that biofilm images with identical structural parameters showed nearly identical activities and substrate concentration profiles. This implies that the set containing all common structural parameters can successfully describe biofilm structure. This finding is significant, as it opens the door to the next step, of finding a smaller standard set of biofilm structural parameters that can be used to compare biofilm structure.

Preconcentration mechanism of trivalent lanthanum on eQCM electrodes in the presence of α-hydroxy isobutyric acid

Electroprecipitation can be used to preconcentrate lanthanum on carbon electrode surfaces. The use of complexing ligands is expected to improve the electroprecipitation of lanthanum by protecting La ions in solution from the alkaline region near the electrode surface. However, the electroprecipitation mechanism of La in the presence of a complexing ligand is not known. The goal of this work is to 1) determine the effect of the complexing ligand, α-hydroxy isobutyric acid (HIBA), on the electroprecipitation of La onto the gold electrodes, and 2) identify the changes in the mechanism of accumulation when preconcentrating in the presence of HIBA. We used an electrochemical quartz crystal microbalance (eQCM) and needle type pH microelectrodes to determine pH near the electrode surface in combination with cyclic voltammetry to understand the electroprecipitation mechanism. We used the bi-dentate ligand HIBA as a ligand and found that lanthanum electroprecipitation is hindered in the presence of HIBA. The presence of HIBA also delayed the onset of film formation during a cyclic voltammetric experiment by ~100 mV compared to experiments performed without HIBA. The shift in onset potential is attributed to the buffering action of HIBA (pK_a = 3.7) since the shift is not present in subsequent scans. The precipitated film was characterized by scanning electron microscopy, X-ray photoelectron spectrometry, and Auger nanoprobe spectrometry. While we found that La(OH)₃ was the predominant chemical state of the film on electrodes in the absence of HIBA, La₂O₃ was found for films created in the presence of HIBA. Our finding demonstrates that La(OH)₃ can be electrodeposited at room temperature.

Electron donor availability controls scale up of anodic biofilms

The scale up of bioelectrochemical systems (BESs) is a challenging problem that limits the advancement and practical implementation of the technology. The goal of this work is to acquire an understanding of the limitations on scaling up anodic biofilms in BESs. We hypothesized that scaling up is dependent on the availability of electron donors. We tested this hypothesis by enriching anodic biofilms on electrodes of multiple sizes (15 cm² to 466 cm²) and quantified the anodic current densities while varying the electron donor concentrations. The anodic biofilms were enriched on electrodes under two conditions: (1) in raw wastewater and (2) in wastewater supplemented with 20 mM acetate. Following anodic biofilm enrichment, the current density for each electrode was quantified in artificial wastewater medium with variable COD loadings using acetate as an electron donor. Current generated using anodic biofilms scaled up at a high COD loading (1500 mg/L), while current density decreased with increasing electrode size at lower COD loadings. Further, microbial community analysis revealed that the microbial community was independent of the electrode size but dependent on the medium composition during the enrichment phase. These results provide a practical framework for the design of large-scale BESs based on laboratory-scale measurements.

The infection of its insect vector by bacterial plant pathogen "Candidatus Liberibacter solanacearum" is associated with altered vector physiology

Many bacterial and viral plant pathogens are transmitted by insect vectors, and pathogen-mediated alterations of plant physiology often influence insect vector behavior and fitness. It remains largely unknown for most plant pathogens whether, and how, they might directly alter the physiology of their insect vectors in ways that promote pathogen transmission. Here we examined whether the presence of "Candidatus Liberibacter solanacearum" ("Ca. L. solanacearum"), an obligate bacterial pathogen of plants and of its psyllid vector alters the physiochemical environment within its insect vector, the potato psyllid (Bactericera cockerelli). Microelectrodes were used to measure the local pH and oxygen tension within the abdomen of "Ca. L. solanacearum"-free psyllids and those infected with "Ca. L. solanacearum". The hemolymph of infected psyllids had higher pH at 9.09 ± 0.12, compared to "Ca. L. solanacearum"-free psyllids (8.32 ± 0.11) and a lower oxygen tension of 33.99% vs. 67.83%, respectively. The physicochemical conditions inside "Ca. L. solanacearum"-free and -infected psyllids body differed significantly with the infected psyllids having a higher hemolymph pH and lower oxygen tension than "Ca. L. solanacearum"-free psyllids. Notably, the bacterial titer increased under conditions of higher pH and lower oxygen tension values. This suggests that the vector's physiology is altered by the presence of the pathogen, potentially, resulting in a more conducive environment for "Ca. L. solanacearum" survival and subsequent transmission.

Responses of Acinetobacter baumannii Bound and Loose Extracellular Polymeric Substances to Hyperosmotic Agents Combined with or without Tobramycin: An Atomic Force Microscopy Study

In this work, contributions of extracellular polymeric substances (EPS) to the nanoscale mechanisms through which the multidrug-resistant Acinetobacter baumannii responds to antimicrobial and hyperosmotic treatments were investigated by atomic force microscopy. Specifically, the adhesion strengths to a control surface of silicon nitride (Si₃N₄) and the lengths of bacterial surface biopolymers of bound and loose EPS extracted from A. baumannii biofilms were quantified after individual or synergistic treatments with hyperosmotic agents (NaCl and maltodextrin) and an antibiotic (tobramycin). In the absence of any treatment, the loose EPS were significantly longer in length and higher in adhesion to Si₃N₄ than the bound EPS. When used individually, the hyperosmotic agents and tobramycin collapsed the A. baumannii bound and loose EPS. The combined treatment of maltodextrin with tobramycin collapsed only the loose EPS and did not alter the adhesion of both bound and loose EPS to Si₃N₄. In addition, the combined treatment was not as effective in collapsing the EPS molecules as when tobramycin was applied alone. Finally, the effects of treatments were dose-dependent. Altogether, our findings suggest that a sequential treatment could be effective in treating A. baumannii biofilms, in which a hyperosmotic agent is used first to collapse the EPS and limit the diffusion of nutrients into the biofilm, followed by the use of an antibiotic to kill the bacterial cells that escape from the biofilm because of starvation.

Hydrogen-Peroxide-Generating Electrochemical Scaffold Eradicates Methicillin-Resistant Staphylococcus aureus Biofilms

Increasing rates of chronic wound infections caused by antibiotic-resistant bacteria are a crisis in healthcare settings. Biofilms formed by bacterial communities in these wounds create a complex environment, enabling bacteria to persist, even with antibiotic treatment. Wound infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are major causes of morbidity in clinical practice. There is a need for new therapeutic interventions not based on antibiotics. Hydrogen peroxide (H2O2) is a known antibacterial/antibiofilm agent, continuous delivery of which has been challenging. A conductive electrochemical scaffold (e-scaffold) is developed, which is composed of carbon fabric that electrochemically reduces dissolved oxygen into H2O2 when polarized at -0.6 VAg/AgCl, as a novel antibiofilm wound dressing material. In this study, the in vitro antibiofilm activity of the e-scaffold against MRSA is investigated. The developed e-scaffold efficiently eradicates MRSA biofilms, based on bacterial quantitation and ATP measurements. Moreover, imaging hinted at the possibility of cell-membrane damage as a mechanism of action. These results suggest that an H2O2-generating e-scaffold may be a novel platform for eliminating MRSA biofilms without using antibiotics and may be useful to treat chronic MRSA wound infections.

Hypochlorous-Acid-Generating Electrochemical Scaffold for Treatment of Wound Biofilms

Biofilm formation causes prolonged wound infections due to the dense biofilm structure, differential gene regulation to combat stress, and production of extracellular polymeric substances. Acinetobacter baumannii, Staphylococcus aureus, and Pseudomonas aeruginosa are three difficult-to-treat biofilm-forming bacteria frequently found in wound infections. This work describes a novel wound dressing in the form of an electrochemical scaffold (e-scaffold) that generates controlled, low concentrations of hypochlorous acid (HOCl) suitable for killing biofilm communities without substantially damaging host tissue. Production of HOCl near the e-scaffold surface was verified by measuring its concentration using needle-type microelectrodes. E-scaffolds producing 17, 10 and 7 mM HOCl completely eradicated S. aureus, A. baumannii, and P. aeruginosa biofilms after 3 hours, 2 hours, and 1 hour, respectively. Cytotoxicity and histopathological assessment showed no discernible harm to host tissues when e-scaffolds were applied to explant biofilms. The described strategy may provide a novel antibiotic-free strategy for treating persistent biofilm-associated infections, such as wound infections.

Design and Finite Element Model of a Microfluidic Platform with Removable Electrodes for Electrochemical Analysis

A microfluidic platform for hydrodynamic electrochemical analysis was developed, consisting of a poly(methyl methacrylate) chip and three removable electrodes, each housed in 1/16" OD polyether ether ketone tube which can be removed independently for polishing or replacement. The working electrode was a 100-μm diameter Pt microdisk, located flush with the upper face of a 150 μm × 20 μm × 3 cm microchannel, smaller than previously reported for these types of removable electrodes. A commercial leak-less reference electrode was utilized, and a coiled platinum wire was the counter electrode. The platform was evaluated electrochemically by oxidizing a potassium ferrocyanide solution at the working electrode, and a typical limiting current behavior was observed after running linear sweep voltammetry and chronoamperometry, with flow rates 1-6 μL/min. While microdisk channel electrodes have been simulated before using a finite difference method in an ideal 3D geometry, here we predict the limiting current using finite elements in COMSOL Multiphysics 5.3a, which allowed us to easily explore variations in the microchannel geometry that have not previously been considered in the literature. Experimental and simulated currents showed the same trend but differed by 41% in simulations of the ideal geometry, which improved when channel and electrode imperfections were included.

Engineering rheology of electrolytes using agar for improving the performance of bioelectrochemical systems

The present study is focused on enhancing the rheological properties of the electrolyte and eliminating sedimentation of microorganisms/flocs without affecting the electron transfer kinetics for improved bioelectricity generation. Agar derived from polysaccharide agarose (0.05-0.2%, w/v) was chosen as a rheology modifying agent. Electroanalytical investigations showed that electrolytes modified with 0.15% agar display a nine-fold increase in current density (1.2 mA/cm²) by a thermophilic strain (Geobacillus sp. 44C, 60 °C) when compared with the control. Sodium phosphate buffer (0.1 M, pH 7) electrolyte with riboflavin (0.1 mM) was used as the control. Electrolytes modified with 0.15% agar significantly improved chemical oxygen demand removal rates. This developed electrolyte will aid in improving bioelectricity generation in Bioelectrochemical Systems (BES). The developed strategy avoids the use of peristaltic pumps and magnetic stirrers, thereby improving the energy efficiency of the process.

Structural and metabolic responses of Staphylococcus aureus biofilms to hyperosmotic and antibiotic stress

Biofilms alter their metabolism in response to environmental stress. This study explores the effect of a hyperosmotic agent-antibiotic treatment on the metabolism of Staphylococcus aureus biofilms through the use of nuclear magnetic resonance (NMR) techniques. To determine the metabolic activity of S. aureus, we quantified the concentrations of metabolites in spent medium using high-resolution NMR spectroscopy. Biofilm porosity, thickness, biovolume, and relative diffusion coefficient depth profiles were obtained using NMR microimaging. Dissolved oxygen concentration was measured to determine the availability of oxygen within the biofilm. Under vancomycin-only treatment, the biofilm communities switched to fermentation under anaerobic condition, as evidenced by high concentrations of formate (7.4 ± 2.7 mM), acetate (13.1 ± 0.9 mM), and lactate (3.0 ± 0.8 mM), and there was no detectable dissolved oxygen in the biofilm. In addition, we observed the highest consumption of pyruvate (0.19 mM remaining from an initial 40 mM concentration), the sole carbon source, under the vancomycin-only treatment. On the other hand, relative effective diffusion coefficients increased from 0.73 ± 0.08 to 0.88 ± 0.08 under vancomycin-only treatment but decreased from 0.71 ± 0.04 to 0.60 ± 0.07 under maltodextrin-only and from 0.73 ± 0.06 to 0.56 ± 0.08 under combined treatments. There was an increase in biovolume, from 2.5 ± 1 mm3 to 7 ± 1 mm3 , under the vancomycin-only treatment, while the maltodextrin-only and combined treatments showed no significant change in biovolume over time. This indicated that physical biofilm growth was halted during maltodextrin-only and combined treatments.

Organismal and spatial partitioning of energy and macronutrient transformations within a hypersaline mat

Phototrophic mat communities are model ecosystems for studying energy cycling and elemental transformations because complete biogeochemical cycles occur over millimeter-to-centimeter scales. Characterization of energy and nutrient capture within hypersaline phototrophic mats has focused on specific processes and organisms; however, little is known about community-wide distribution of and linkages between these processes. To investigate energy and macronutrient capture and flow through a structured community, the spatial and organismal distribution of metabolic functions within a compact hypersaline mat community from Hot Lake have been broadly elucidated through species-resolved metagenomics and geochemical, microbial diversity and metabolic gradient measurements. Draft reconstructed genomes of 34 abundant organisms revealed three dominant cyanobacterial populations differentially distributed across the top layers of the mat suggesting niche separation along light and oxygen gradients. Many organisms contained diverse functional profiles, allowing for metabolic response to changing conditions within the mat. Organisms with partial nitrogen and sulfur metabolisms were widespread indicating dependence on metabolite exchange. In addition, changes in community spatial structure were observed over the diel. These results indicate that organisms within the mat community have adapted to the temporally dynamic environmental gradients in this hypersaline mat through metabolic flexibility and fluid syntrophic interactions, including shifts in spatial arrangements.

Trade-offs between microbiome diversity and productivity in a stratified microbial mat

Productivity is a major determinant of ecosystem diversity. Microbial ecosystems are the most diverse on the planet yet very few relationships between diversity and productivity have been reported as compared with macro-ecological studies. Here we evaluated the spatial relationships of productivity and microbiome diversity in a laboratory-cultivated photosynthetic mat. The goal was to determine how spatial diversification of microorganisms drives localized carbon and energy acquisition rates. We measured sub-millimeter depth profiles of net primary productivity and gross oxygenic photosynthesis in the context of the localized microenvironment and community structure, and observed negative correlations between species richness and productivity within the energy-replete, photic zone. Variations between localized community structures were associated with distinct taxa as well as environmental profiles describing a continuum of biological niches. Spatial regions in the photic zone corresponding to high primary productivity and photosynthesis rates had relatively low-species richness and high evenness. Hence, this system exhibited negative species-productivity and species-energy relationships. These negative relationships may be indicative of stratified, light-driven microbial ecosystems that are able to be the most productive with a relatively smaller, even distributions of species that specialize within photic zones.

Syntrophic anaerobic photosynthesis via direct interspecies electron transfer

Microbial phototrophs, key primary producers on Earth, use H₂O, H₂, H₂S and other reduced inorganic compounds as electron donors. Here we describe a form of metabolism linking anoxygenic photosynthesis to anaerobic respiration that we call ‘syntrophic anaerobic photosynthesis'. We show that photoautotrophy in the green sulfur bacterium Prosthecochloris aestaurii can be driven by either electrons from a solid electrode or acetate oxidation via direct interspecies electron transfer from a heterotrophic partner bacterium, Geobacter sulfurreducens. Photosynthetic growth of P. aestuarii using reductant provided by either an electrode or syntrophy is robust and light-dependent. In contrast, P. aestuarii does not grow in co-culture with a G. sulfurreducens mutant lacking a trans-outer membrane porin-cytochrome protein complex required for direct intercellular electron transfer. Syntrophic anaerobic photosynthesis is therefore a carbon cycling process that could take place in anoxic environments. This process could be exploited for biotechnological applications, such as waste treatment and bioenergy production, using engineered phototrophic microbial communities.

Direct interspecies electron transfer has been shown in methane-producing communities, but it is unknown how widespread this mechanism is. Here, Ha et al. show that anoxygenic photosynthesis can be driven by direct electron transfer from a heterotrophic partner bacterium.

Maltodextrin enhances biofilm elimination by electrochemical scaffold

Electrochemical scaffolds (e-scaffolds) continuously generate low concentrations of H₂O₂ suitable for damaging wound biofilms without damaging host tissue. Nevertheless, retarded diffusion combined with H₂O₂ degradation can limit the efficacy of this potentially important clinical tool. H₂O₂ diffusion into biofilms and bacterial cells can be increased by damaging the biofilm structure or by activating membrane transportation channels by exposure to hyperosmotic agents. We hypothesized that e-scaffolds would be more effective against Acinetobacter baumannii and Staphylococcus aureus biofilms in the presence of a hyperosmotic agent. E-scaffolds polarized at -600 mV_Ag/AgCl were overlaid onto preformed biofilms in media containing various maltodextrin concentrations. E-scaffold alone decreased A. baumannii and S. aureus biofilm cell densities by (3.92 ± 0.15) log and (2.31 ± 0.12) log, respectively. Compared to untreated biofilms, the efficacy of the e-scaffold increased to a maximum (8.27 ± 0.05) log reduction in A. baumannii and (4.71 ± 0.12) log reduction in S. aureus biofilm cell densities upon 10 mM and 30 mM maltodextrin addition, respectively. Overall ~55% decrease in relative biofilm surface coverage was achieved for both species. We conclude that combined treatment with electrochemically generated H₂O₂ from an e-scaffold and maltodextrin is more effective in decreasing viable biofilm cell density.