Biofilm Development

RpoN mediates biofilm formation by directly controlling vps gene cluster and c-di-GMP synthetic metabolism in V. alginolyticus

Vibrio alginolyticus is a prevalent pathogen in both humans and marine species, exhibiting high adaptability to various adverse environmental conditions. Our previous studies have shown that ΔrpoN formed three enhanced biofilm types, including spectacular surface-attached biofilm (SB), scattered pellicle biofilm (PB), and colony rugosity. However, the precise mechanism through which rpoN regulates biofilm formation has remained unclear. Based on the critical role of Vibrio exopolysaccharide (VPS) in biofilm formation, several genes related to the production and regulation of VPS were characterized in V. alginolyticus. Our findings from mutant strains indicated that VPS has complete control over the formation of rugose colony morphology and PB, while it only partially contributes to SB formation. Among the four transcriptional regulators of the vps gene cluster, vpsR and VA3545 act as promoters, whereas VA3546 and VA2703 function as repressors. Through transcriptome analysis and c-di-GMP concentration determination, VA0356 and VA3580 which encoded diguanylate cyclase were found to mediate the ΔrpoN biofilm formation. As a central regulator, rpoN governed biofilm formation through two regulatory pathways. Firstly, it directly bound to the upstream region of VA4206 to regulate the expression of the vps gene cluster (VA4206-VA4196). Secondly, it directly and indirectly modulated c-di-GMP synthesis gene VA3580 and VA0356, respectively, thereby affecting c-di-GMP concentration and subsequently influencing the expression of vps transcription activators vpsR and VA3545. Under conditions promoting SB formation, ΔrpoN was unable to thrive below the liquid level due to significantly reduced activities of three catalytic enzymes (ACK, ADH, and ALDH) involved in pyruvate metabolism, but tended to reproduce in air-liquid interface, a high oxygen niche compared to the liquid phase. In conclusion, both exopolysaccharide synthesis and oxygen-related metabolism contributed to ΔrpoN biofilm formation. The role of RpoN-mediated hypoxic metabolism and biofilm formation were crucial for comprehending the colonization and pathogenicity of V. alginolyticus in hosts, providing a novel target for treating V. alginolyticus in aquatic environments and hosts.

Calcium signaling controls early stage biofilm formation and dispersal in Vibrio fischeri

Bacterial dispersal from a biofilm is presently the least-studied step of the biofilm life cycle. The symbiotic bacterial species Vibrio fischeri is a model organism for studying biofilms relevant to a eukaryotic host; however, methodology is lacking to readily study the dispersal of this microbe from biofilms formed in the lab. Here, we adapted a time-lapse assay to visualize biofilm dispersal by V. fischeri. We observed biofilm formation and dispersal for multiple V. fischeri isolates, which displayed a variety of biofilm architecture phenotypes and dispersal dynamics. We then investigated V. fischeri strain ES114 using genetic tools and mutants available for this strain. ES114 exhibited calcium-dependent biofilm formation followed by a rapid (less than 10 min) coordinated dispersal event that occurred approximately 5 h from the experimental start. Biofilm dispersal was largely independent of the dispersal-promoting protease encoded by lapG. Although we found no role under our conditions for either biofilm formation or dispersal for several other factors including polysaccharides and autoinducers, we determined that biofilm formation was enhanced, and dispersal was delayed, with increased concentrations of calcium. Furthermore, biofilm formation depended on the calcium-responsive diguanylate cyclase (DGC) CasA, and dispersal could be modulated by overexpressing CasA. Our work has thus developed a new tool for the V. fischeri field and uncovered a key role for calcium signaling and c-di-GMP in early biofilm formation and dispersal in V. fischeri.

IMPORTANCE

Biofilm formation and dispersal are critical steps in both symbiotic and pathogenic colonization. Relative to biofilm formation, the process of dispersal in the model symbiont Vibrio fischeri, and other bacteria, is understudied. Here, we adapted an imaging assay to study early biofilm formation and the dispersal process in V. fischeri. We demonstrated that our assay can quantify biofilm formation and dispersal over time, can reveal phenotypic differences in diverse natural wild-type isolates, and is sensitive enough to investigate the impact of environmental factors. Our data confirm that calcium is a potent biofilm formation signal and identify the diguanylate cyclase CasA as a key regulator. This work leads the way for more in-depth research about unknown mechanisms of biofilm dispersal.

Formation of Streptococcus mutans Polymicrobial Biofilms in the Presence of Lactobacillus plantarum and Candida albicans

Dental caries is an infectious disease that develops through biofilm. Streptococcus mutans is a cariogenic bacterium that can be found in dental plaque. Streptococcus mutans regulates biofilm formation and communicate with other microbes through a process called quorum sensing. Dental caries prevention can be achieved by inhibiting quorum sensing. This study aimed to investigate the ability of Lactobacillus plantarum and Candida albicans to inhibit the formation of S. mutans polymicrobial biofilms. This study aims to investigate the ability of biofilm formation analyzed through the crystal violet (CV) assay and bacterial metabolic activity analyzed through the methylthiazol tetrazolium (MTT) assay. The bacteria used are S. mutans (serotype C), L. plantarum (FNCC 0020), and C. albicans.CV assay results show that in the presence of L. plantarum, biofilm formation in S. mutans decreases (9.5%). Meanwhile, the formation of S. mutans biofilms increased with the presence of C. albicans (28.8%). MTT assay results showed an increase in the metabolic activity of S. mutans in the presence of L. plantarum (20.2%) and C. albicans (19.4%). Lactobacillus plantarum can inhibit the formation of S. mutans biofilms, while C. albicans can increase S. mutans biofilms.

Histopathology is More Reliable Than Microbiology for Detecting Residual Osteomyelitis After Conservative Surgery for Diabetic Foot: The Pitfall of False-Positive Cultures and the Role of Pseudomonas aeruginosa

The optimal method for assessing residual osteomyelitis after conservative surgery for diabetic foot infection remains controversial. Microbiological cultures are frequently used due to their rapid turnaround and utility in guiding antibiotic therapy, but their diagnostic reliability is uncertain. This study compared microbiological cultures and histopathology in evaluating bone resection margins, using histopathology as the gold standard. We included 93 patients undergoing conservative surgery for diabetic foot osteomyelitis. Bone samples were obtained from the proximal resection margin for both microbiology and histopathology. A microbiological result was considered contamination when cultures were positive but histopathology was negative. Microbiological cultures at bone resection margins yielded 52 true positives, 23 false positives (contamination), 10 false negatives, and 8 true negatives when compared to histopathology. This resulted in a sensitivity of 83.9%, specificity of 25.8%, positive predictive value of 69.3%, and negative predictive value of 44.4%. Contamination was not associated with the severity of infection, presence of soft tissue involvement, inflammatory markers, or glycemic control. No association was found between contamination and polymicrobial flora in the primary surgical specimen. However, Pseudomonas aeruginosa was the only species significantly associated with contamination (p = .008), suggesting species-specific factors may contribute to microbiological false positives. These findings emphasize that microbiology, while sensitive, is not a specific method for assessing residual bone infection and should not be used in isolation. Histopathology remains the more reliable diagnostic tool. Future research should explore biofilm-targeted strategies and intraoperative antiseptic protocols to reduce contamination of bone biopsy specimens obtained from resection margins.

Modulation of the biological response to surfaces through the controlled deposition of 3D polymeric surfactants

Biomaterials play a crucial role in modern medicine through their use as medical implants and devices. However, they can support biofilm formation and infection, and lack integration with the surrounding human tissue at the implant site. This work reports the development of novel poly(ethyl acrylate) (PEA) based copolymers that address both issues. These PEA materials were molecularly designed polymeric surfactants (surfmers) synthesised via controlled radical polymerisations to achieve different polymeric architectures, (i.e., statistical and block copolymers). These were both deposited as structured 2D films on glass coverslips and used to manufacture monodisperse 3D micro-particles with functional surfaces (via microfluidics). ToF-SIMS was used to analyse these 2D and 3D surfaces to understand: (a) the surface arrangement of the monomer sequences exhibited by the different polymer structures and (b) how this surface monomer arrangement influenced mammalian fibroblast cell and/or Staphylococcus aureus behaviour at these film/particle surfaces. In addition, the form of the fibronectin (FN) network assembly's importance in promoting growth factor (GF) binding was probed using atomic force microscopy (AFM) on the 2D films. This confirmed that specific surfmer molecular surface organisations were achieved during film/micro-particle fabrication, which presented exterior functionalities that either prevent biofilm attachment or promote the formation of structured FN networks for GF binding.

Staphylococcus biofilm dynamics and antibiotic resistance: insights into biofilm stages, zeta potential dynamics, and antibiotic susceptibility

Staphylococcus spp. infections often involve biofilms, but standard antibiotic minimum inhibitory concentration (MIC) testing used to determine treatment evaluates planktonic bacterial growth only and does not account for biofilm presence, strength, or growth stage. To aid in determining a cost-effective method to solve this issue, we built upon in vitro methods initially published by Stepanovic et al. used to determine weak and strong biofilm formations. First, we determined 115 unique S. aureus isolate biofilms at 2, 4, 6, 8, 16, and 24 h to classify the hourly stages of biofilm development based on statistically significant final growth results (P < 0.001): stages one (0-6 h), two (6-16 h), three (16-24 h), and four (>24 h). Next, to further evaluate in vitro biofilm strength, electrostatic differences were measured through zeta (ζ)-potential for strong and weak biofilm producers at early and late stage-formed biofilms. The early stages of weak biofilm formers had a greater negative electrostatic charge when compared to strong biofilm formers. Meanwhile, strong biofilm formers began early stages with less negative charges before increasing the negative electrostatic charge by stage-four biofilm. At all time points, weak biofilm-forming isolate mean ζ-potentials were significantly more negative than strong biofilm formers (P = ≤0.04). Finally, to elucidate minimum eradication concentrations for biofilms, we treated stage-four biofilms with progressively higher concentrations of either daptomycin, vancomycin, or levofloxacin. Daptomycin was the only antibiotic to achieve ≥75% reduction in biofilm viability, seen at 32-256 μg/mL (64-512× MIC), and significantly reduced residual biofilm across all strong and weak biofilms. Biofilm findings showed an unexpected initial biofilm decrease in response to lower concentrations of antibiotics, followed by an increase in biofilm biomass at higher antibiotic concentrations. While higher antibiotic concentrations can be used to overcome bacterial resistance and eliminate infections, our results suggest that antimicrobial resistance is observed, regardless of bacterial biofilm strength, and that there may be an optimal treatment concentration window for achieving maximum kill. Our data add to the increasing evidence of biofilms' role in recurrent infections and the importance of antibiotic concentration.IMPORTANCEThis work is significant, as it addresses a critical gap in standard antibiotic testing by focusing on the unique characteristics of biofilm-forming Staphylococcus aureus infections, which are major contributors to recurrent and chronic infections. Unlike traditional MIC testing that evaluates planktonic bacteria, this study emphasizes the importance of biofilm presence, growth stages, and electrostatic properties in determining treatment strategies. By classifying biofilm development into distinct stages in an easily reproducible assay and measuring the biofilm zeta-potential for key differences and overall biofilm response to multiple standard antibiotic concentrations, this research provides valuable insights for the future of biofilm in vitro work. Furthermore, it highlights the efficacy of daptomycin in eradicating biofilm while identifying possibilities of optimal antibiotic concentration windows, a critical consideration for mitigating resistance and achieving effective infection control. These findings underscore the necessity of tailoring treatment to biofilm-specific dynamics, offering a path toward more effective therapeutic approaches for biofilm-associated infections.

Sodium dichloroisocyanurate: a promising candidate for the disinfection of resilient drain biofilm

Background

Biofilms are complex multicellular communities of microorganisms embedded within a protective matrix which confers resistance to various antimicrobials, including biocides. Biofilms can cause a range of human diseases and are responsible for 1.7 million hospital-acquired infections in the US annually, providing an economic burden of $11.5 billion in treatment costs. Biofilm contained within drain and plumbing systems may contain pathogenic viruses and bacteria which pose a significant risk to patient safety within healthcare environments.

Aim

The aim of this study was to determine if three hospital-grade disinfectants (sodium dichloroisocyanurate, peracetic acid and sodium hypochlorite) were capable of killing microorganisms within biofilm, and thus, determining their potential as candidates for drain biofilm disinfection.

Methods

Pseudomonas aeruginosa biofilms were cultivated using the CDC biofilm reactor, a standardised method for determining disinfectant efficacy against biofilm within the United States of America. Each disinfectant was tested using a one-minute contact time, using the highest concentration available on the product label.

Findings

The sodium dichloroisocyanurate product was successful in killing biofilm microorganisms, resulting in a log reduction of ≥ 8.70. Peracetic acid reduced biofilm by 3.82 log10 units, followed by sodium hypochlorite, which produced a reduction of 3.78 log10 units.

Conclusions

The use of a highly effective disinfectant with proven biofilm efficacy can help ensure patient safety and reduce infection levels. Drains and plumbing systems provide a reservoir for potential pathogens and biofilm; thus, drain disinfection is critical in reducing the instance of hospital-acquired infections. Sodium dichloroisocyanurate may provide a reliable solution for drain applications and subsequently, patient wellbeing and safety.

Overcoming antibiotic resistance: the potential and pitfalls of drug repurposing

Since its emergence shortly after the discovery of penicillin, antibiotic resistance has escalated dramatically, posing a significant health threat and economic burden. Drug repositioning, or drug repurposing, involves identifying new therapeutic applications for existing drugs, utilising their established safety profiles and pharmacological data to swiftly provide effective treatments against resistant pathogens. Several drugs, including otilonium bromide, penfluridol, eltrombopag, ibuprofen, and ceritinib, have demonstrated potent antibacterial activity against multidrug-resistant (MDR) bacteria. These drugs can disrupt biofilms, damage bacterial membranes, and inhibit bacterial growth. The combination of repurposed drugs with conventional antibiotics can reduce the required dosage of individual drugs, mitigate side effects, and delay the development of resistance, making it a promising strategy against MDR bacteria such as Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. Despite its promise, drug repurposing faces challenges such as potential off-target effects, toxicity, and regulatory and intellectual property issues, necessitating rigorous evaluations and strategic solutions. This article aims to explore the potential of drug repurposing as a strategy to combat antibiotic resistance, examining its benefits, challenges, and future prospects. We address the legal, economic, and practical challenges associated with repurposing existing drugs, highlight successful examples, and propose solutions to enhance the efficacy and viability of this approach in combating MDR bacterial infections.

Applying a polysaccharide lyase from Stenotrophomonas maltophilia to disrupt alginate exopolysaccharide produced by Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa is considered one of the most challenging, drug-resistant, opportunistic pathogens partly due to its ability to synthesize robust biofilms. Biofilm is a mixture of extracellular polymeric substances (EPS) that encapsulates microbial cells, leading to immune evasion, antibiotic resistance, and thus higher risk of infection. In the cystic fibrosis lung environment, P. aeruginosa undergoes a mucoid transition, defined by overproduction of the exopolysaccharide alginate. Alginate encapsulation results in bacterial resistance to antibiotics and the host immune system. Given its role in airway inflammation and chronic infection, alginate is an obvious target to improve treatment for P. aeruginosa infection. Previously, we demonstrated polysaccharide lyase Smlt1473 from Stenotrophomonas maltophilia strain k279a can catalyze the degradation of multiple polyuronides in vitro, including D-mannuronic acid (poly-ManA). Poly-ManA is a major constituent of P. aeruginosa alginate, suggesting that Smlt1473 could have potential application against multidrug-resistant P. aeruginosa and perhaps other microbes with related biofilm composition. In this study, we demonstrate that Smlt1473 can inhibit and degrade alginate from P. aeruginosa. Additionally, we show that tested P. aeruginosa strains are dominant in acetylated alginate and that all but one have similar M-to-G ratios. These results indicate that variation in enzyme efficacy among the isolates is not primarily due to differences in total EPS or alginate chemical composition. Overall, these results demonstrate Smlt1473 can inhibit and degrade P. aeruginosa alginate and suggest that other factors including rate of EPS production, alginate sequence/chain length, or non-EPS components may explain differences in enzyme efficacy.

IMPORTANCE

Pseudomonas aeruginosa is a major opportunistic human pathogen in part due to its ability to synthesize biofilms that confer antibiotic resistance. Biofilm is a mixture of polysaccharides, DNA, and proteins that encapsulate cells, protecting them from antibiotics, disinfectants, and other cleaning agents. Due to its ability to increase antibiotic and immune resistance, the exopolysaccharide alginate plays a large role in airway inflammation and chronic P. aeruginosa infection. As a result, colonization with P. aeruginosa is the leading cause of morbidity and mortality in CF patients. Thus, it is an obvious target to improve the treatment regimen for P. aeruginosa infection. In this study, we demonstrate that polysaccharide lyase, Smlt1473, inhibits alginate secretion and degrades established alginate from a variety of mucoid P. aeruginosa clinical isolates. Additionally, Smlt1473 differs from other alginate lyases in that it is active against acetylated alginate, which is secreted during chronic lung infection. These results suggest that Smlt1473 may be useful in treating infections associated with alginate-producing P. aeruginosa, as well as have the potential to reduce P. aeruginosa EPS in non-clinical settings.

Fluoroquinolones and Biofilm: A Narrative Review

Background: Biofilm-associated infections frequently span multiple body sites and represent a significant clinical challenge, often requiring a multidisciplinary approach involving surgery and antimicrobial therapy. These infections are commonly healthcare-associated and frequently related to internal or external medical devices. The formation of biofilms complicates treatment, as they create environments that are difficult for most antimicrobial agents to penetrate. Fluoroquinolones play a critical role in the eradication of biofilm-related infections. Numerous studies have investigated the synergistic potential of combining fluoroquinolones with other chemical agents to augment their efficacy while minimizing potential toxicity. Comparative research suggests that the antibiofilm activity of fluoroquinolones is superior to that of beta-lactams and glycopeptides. However, their activity remains less effective than that of minocycline and fosfomycin. Noteworthy combinations include fluoroquinolones with fosfomycin and aminoglycosides for enhanced activity against Gram-negative organisms and fluoroquinolones with minocycline and rifampin for more effective treatment of Gram-positive infections. Despite the limitations of fluoroquinolones due to the intrinsic characteristics of this antibiotic, they remain fundamental in this setting thanks to their bioavailability and synergisms with other drugs. Methods: A comprehensive literature search was conducted using online databases (PubMed/MEDLINE/Google Scholar) and books written by experts in microbiology and infectious diseases to identify relevant studies on fluoroquinolones and biofilm. Results: This review critically assesses the role of fluoroquinolones in managing biofilm-associated infections in various clinical settings while also exploring the potential benefits of combination therapy with these antibiotics. Conclusions: The literature predominantly consists of in vitro studies, with limited in vivo investigations. Although real world data are scarce, they are in accordance with fluoroquinolones' effectiveness in managing early biofilm-associated infections. Also, future perspectives of newer treatment options to be placed alongside fluoroquinolones are discussed. This review underscores the role of fluoroquinolones in the setting of biofilm-associated infections, providing a comprehensive guide for physicians regarding the best use of this class of antibiotics while highlighting the existing critical issues.

The role of universal stress protein Usp1413 in meropenem adaptive resistance and environmental stress responses in Acinetobacter baumannii

Although various mechanisms of carbapenem-resistance have been identified in the nosocomial pathogen Acinetobacter baumannii, the critical process of resistance evolution and the factors involved in are not well understood. Herein, we identified a universal stress protein Usp1413 which played an important role in adaptive resistance of A. baumannii to meropenem (MEM). Based on RNA-Seq and genome sequencing, Usp1413 was not only one of the most downregulated USPs, but also the bare one having mutation of tyrosine and glycine inserted at the site of 229-230 (YG229-230) under the stimulation of MEM. Deletion of Usp1413 resulted in increased MEM resistance. In addition, Usp1413 affected the bacterial abilities of biofilm formation and swarm motility, as well as helped A. baumannii response to various environmental stresses. These effects of Usp1413 were achieved by regulating its interaction proteins, within the functions of YigZ family protein, acetyltransferase, and SulP family inorganic anion transporter. The insertion mutation of YG229-230 influenced both the expression of interaction proteins and the phenotypes of bacteria. Finally, the promotor region of Usp1413 was convinced by point mutations. Overall, our findings identified the universal stress protein Usp1413 as a contributor involved in MEM adaptive resistance and responded to numerous environmental stresses. This study provides novel insights into the mechanism of universal stress proteins in participating antibiotic resistance, and affords a potential target for controlling drug resistance development in A. baumannii.

The dynamics of biofilm development and dispersal should be taken into account when quantifying biofilm via the crystal violet microtiter plate assay

The crystal violet microtiter plate biofilm assay is often used to compare the amount of biofilm formed by a mutant versus wild-type or a compound-treated biofilm versus the non-treatment control. In many of these studies the amount of biofilm is assessed only at one single time point. However, if the dynamics of biofilm development of the mutant (or compound-treated biofilm) is different than that of the wild-type (or non-treatment control), then biofilm quantification at a single time point may give misleading results. To overcome this shortcoming of the common biofilm quantification technique, we recommend to use a serial dilution-based crystal violet microtiter plate biofilm assay for easy assessment of the dynamics of biofilm development and dispersal. We demonstrate that the dilution-resolved crystal violet assay displays the dynamics of Pseudomonas aeruginosa biofilm development and dispersal as efficient as a time-resolved crystal violet assay. In addition, focusing on mutants of different parts of the c-di-GMP signaling system in P. aeruginosa, we provide an example illustrating the need to assess biofilm dynamics instead of quantifying biofilm biomass at a single time point.

Role of fimbriae variations in Porphyromonas gulae biofilm formation

OBJECTIVES

Porphyromonas gulae is a major causative agent of periodontal disease in companion animals that possesses various virulence factors, including fimbriae, lipopolysaccharides, and proteases. P. gulae fimbriae are classified into three genotypes (A, B, and C) based on their nucleotide sequences. Type C fimbrial isolates have been reported to be more virulent than other fimA types, suggesting that different fimA types may aid in the regulation of periodontal pathogenesis. Detailed findings regarding the ability of P. gulae to form biofilms have yet to be reported. Here, we investigated the contributions of fimbrial genotypes in P. gulae biofilm formation.

METHODS

P. gulae and P. gingivalis biofilms were generated on plates and analyzed using confocal laser microscopy. Additionally, the biofilms formed were assessed by staining with crystal violet. Furthermore, the physical strength of P. gulae biofilms was examined by ultrasonication.

RESULTS

Biofilms formed by P. gulae type C were denser than those formed by types A and B. Moreover, the amount of biofilm formed by type C strains was significantly greater than that formed by type A and B strains, which was similar to the biofilms formed by P. gingivalis with type II fimbriae. Additionally, the physical strength of the type C biofilm was significantly greater than that of the other strains.

CONCLUSIONS

These results suggest that FimA variation may coordinate for biofilm formation. This is the first report on the observation and characterization of P. gulae biofilm formation.

Harnessing microbial biofilms in soil ecosystems: Enhancing nutrient cycling, stress resilience, and sustainable agriculture

Soil ecosystems are complex networks of microorganisms that play pivotal roles in nutrient cycling, stress resilience, and the provision of ecosystem services. Among these microbial communities, soil biofilms, and complex aggregations of microorganisms embedded within extracellular polymeric substances (EPS) exert significant influence on soil health and function. This review delves into the dynamics of soil biofilms, highlighting their structural intricacies and the mechanisms by which they facilitate nutrient cycling, and discusses how biofilms enhance the degradation of pollutants through the action of extracellular enzymes and horizontal gene transfer, contributing to soil detoxification and fertility. Furthermore, the role of soil biofilms in stress resilience is underscored, as they form symbiotic relationships with plants, bolstering their growth and resistance to environmental stressors. The review also explores the ecological functions of biofilms in enhancing soil structure stability by promoting aggregate formation, which is crucial for water retention and aeration. By integrating these insights, we aim to provide a comprehensive understanding of the multifaceted benefits of biofilms in soil ecosystems. This knowledge is essential for developing strategies to manipulate soil biofilms to improve agricultural productivity and ecological sustainability. This review also identifies research gaps and emphasizes the need for practical applications of biofilms in sustainable agriculture.

Interactions of biofilm polysaccharides produced by human infective bacteria with molecules of the quorum sensing system. A microscopy and NMR study

Biofilms are the most common lifestyle adopted by bacterial communities where cells live embedded in a self-produced hydrated matrix. Although polysaccharides are considered essential for matrix architecture, their possible functional roles are still rather unexplored. The primary structure of polysaccharides produced by Klebsiella pneumoniae and species of the Burkholderia cepacia Complex revealed a composition rich in rhamnose. The methyl group on carbon 6 of rhamnose units lowers the polymer hydrophilicity and can form low polarity regions on the polysaccharide chains. These regions promote chain-chain interactions that contribute to the biofilm matrix stability, but may also act as binding sites for low-polarity molecules, aiding their mobility through the hydrated matrix. In particular, quorum sensing system components crucial for the biofilm life cycle often display poor solubility in water. Therefore, cis-11-methyl-2-dodecenoic acid and L-homoserine-lactones were investigated by NMR spectroscopy for their possible interaction with polysaccharides. In addition, the macromolecular morphology of the polysaccharides was assessed using atomic force and electron microscopies to define the role of Rha residues on the three-dimensional conformation of the polymer. NMR data revealed that quorum sensing components interact with Rhamnose-rich polysaccharides, and the extent of interaction depends on the specific primary structure of each polysaccharide.

Cyclic di-GMP as an antitoxin regulates bacterial genome stability and antibiotic persistence in biofilms

Biofilms are complex bacterial communities characterized by a high persister prevalence, which contributes to chronic and relapsing infections. Historically, persister formation in biofilms has been linked to constraints imposed by their dense structures. However, we observed an elevated persister frequency accompanying the stage of cell adhesion, marking the onset of biofilm development. Subsequent mechanistic studies uncovered a comparable type of toxin-antitoxin (TA) module (TA-like system) triggered by cell adhesion, which is responsible for this elevation. In this module, the toxin HipH acts as a genotoxic deoxyribonuclease, inducing DNA double strand breaks and genome instability. While the second messenger c-di-GMP functions as the antitoxin, exerting control over HipH expression and activity. The dynamic interplay between c-di-GMP and HipH levels emerges as a crucial determinant governing genome stability and persister generation within biofilms. These findings unveil a unique TA system, where small molecules act as the antitoxin, outlining a biofilm-specific molecular mechanism influencing genome stability and antibiotic persistence, with potential implications for treating biofilm infections.

The influence of maggot debridement therapy on the bacterial flora of hard-to-heal wounds

OBJECTIVE

Maggot debridement therapy (MDT) is increasingly being used in clinical practice as an alternative treatment for hard-to-heal (chronic) wounds. Among the many benefits of using MDT is its antimicrobial effect. Maggots secrete substances that are known to have antibacterial properties against both Gram-negative and Gram-positive bacteria. Clinically, this results in the effective eradication of pathogenic species and consequently, a faster healing process. The aim of this study was to evaluate the effect MDT has on the bacterial flora of hard-to-heal ulcers.

METHOD

Patients with venous, mixed arteriovenous, decubitus, diabetic and neuropathic wounds were treated with larvae of Lucilia sericata enclosed in bags. Dressings were applied to the wounds for 72 hours. Before and after the therapy, a swab was taken from the wound, and bacterial diversity and bacterial growth scores were assessed. While 16 patients were treated only once, the treatment had to be repeated in four cases until the wounds were fully debrided.

RESULTS

Bacteria of the species Pseudomonas aeruginosa, Proteus mirabilis, Staphylococcus aureus and Enterococcus faecalis were the most common strains observed. Of the 20 patients treated, the total number of bacterial strains decreased in eight wounds, but increased in five wounds, while no difference was observed in nine wounds. The average number of bacterial strains in wounds decreased after MDT. A lower incidence of alarm pathogens was also reported. In cases where multiple applications of larvae were administered, greater decreases in bacterial growth scores were observed than in cases with a single application of dressing (37.5% vs 18.1%, respectively). In 18 cases, after disinfection of the wound by larvae, it was reinfected by strains not detected before. Wounds healed completely after MDT in two patients.

CONCLUSION

In this study, MDT changed the bacterial diversity of hard-to-heal wounds. The larvae reduced overall bacterial growth scores and acted on both Gram-positive and Gram-negative bacteria as well as on alarm pathogens. Cleaned wounds appeared to become vulnerable to infection by opportunistic bacteria. The bacterial burden decreased as the number of applications of biological dressings increased.

Mechanisms of antimicrobial resistance in biofilms

Most bacteria in nature exist in aggregated communities known as biofilms, and cells within a biofilm demonstrate major physiological changes compared to their planktonic counterparts. Biofilms are associated with many different types of infections which can have severe impacts on patients. Infections involving a biofilm component are often chronic and highly recalcitrant to antibiotic therapy as a result of intrinsic physical factors including extracellular matrix production, low growth rates, altered antibiotic target production and efficient exchange of resistance genes. This review describes the biofilm lifecycle, phenotypic characteristics of a biofilm, and contribution of matrix and persister cells to biofilms intrinsic tolerance to antimicrobials. We also describe how biofilms can evolve antibiotic resistance and transfer resistance genes within biofilms. Multispecies biofilms and the impacts of various interactions, including cooperation and competition, between species on tolerance to antimicrobials in polymicrobial biofilm communities are also discussed.

Intestinal biofilms: pathophysiological relevance, host defense, and therapeutic opportunities

SUMMARYThe human intestinal tract harbors a profound variety of microorganisms that live in symbiosis with the host and each other. It is a complex and highly dynamic environment whose homeostasis directly relates to human health. Dysbiosis of the gut microbiota and polymicrobial biofilms have been associated with gastrointestinal diseases, including irritable bowel syndrome, inflammatory bowel diseases, and colorectal cancers. This review covers the molecular composition and organization of intestinal biofilms, mechanistic aspects of biofilm signaling networks for bacterial communication and behavior, and synergistic effects in polymicrobial biofilms. It further describes the clinical relevance and diseases associated with gut biofilms, the role of biofilms in antimicrobial resistance, and the intestinal host defense system and therapeutic strategies counteracting biofilms. Taken together, this review summarizes the latest knowledge and research on intestinal biofilms and their role in gut disorders and provides directions toward the development of biofilm-specific treatments.

DUF1127-containing protein and ProQ had opposite effects on biofilm formation in Vibrio alginolyticus

The RNA binding protein is crucial for gene regulation at the post transcription level. In this study, functions of the DUF1127-containing protein and ProQ, which are RNA-binding proteins, were revealed in Vibrio alginolyticus. DUF1127 deletion increased the ability of biofilm formation, whereas ProQ deletion reduced the amount of biofilm. Moreover, extracellular proteinase secretion was significantly reduced in the DUF1127 deletion strain. ProQ, not DUF1127-containing protein, can help the cell to defense oxidative stress. Deletion of DUF1127 resulted in a higher ROS level in the cell, however, ProQ deletion showed no difference. RNA-seq unveiled the expression of genes involved in extracellular protease secretion were significantly downregulated and biofilm synthesis-related genes, such as rbsB and alsS, were differentially expressed in the DUF1127 deletion strain. ProQ affected the expression of genes involved in biofilm synthesis (flgC and flgE), virulence (betB and hutG), and oxidative stress. Moreover, the DUF1127-containing and ProQ affected the mRNA levels of various regulators, such as LysR and BetI. Overall, our study revealed that the DUF1127-containing protein and ProQ have crucial functions on biofilm formation in V. alginolyticus.

Current strategies for monitoring and controlling bacterial biofilm formation on medical surfaces

Biofilms, intricate microbial communities that attach to surfaces, especially medical devices, form an exopolysaccharide matrix, which enables bacteria to resist environmental pressures and conventional antimicrobial agents, leading to the emergence of multi-drug resistance. Biofilm-related infections associated with medical devices are a significant public health threat, compromising device performance. Therefore, developing effective methods for supervising and managing biofilm growth is imperative. This in-depth review presents a systematic overview of strategies for monitoring and controlling bacterial biofilms. We first outline the biofilm creation process and its regulatory mechanisms. The discussion then progresses to advancements in biosensors for biofilm detection and diverse treatment strategies. Lastly, this review examines the obstacles and new perspectives associated with this domain to facilitate the advancement of innovative monitoring and control solutions. These advancements are vital in combating the spread of multi drug-resistant bacteria and mitigating public health risks associated with infections from biofilm formation on medical instruments.

Molecular mechanisms of DNase inhibition of early biofilm formation Pseudomonas aeruginosa or Staphylococcus aureus: A transcriptome analysis

In vitro studies show that DNase can inhibit Pseudomonas aeruginosa and Staphylococcus aureus biofilm formation. However, the underlying molecular mechanisms remain poorly understood. This study used an RNA-sequencing transcriptomic approach to investigate the mechanism by which DNase I inhibits early P. aeruginosa and S. aureus biofilm formation on a transcriptional level, respectively. A total of 1171 differentially expressed genes (DEGs) in P. aeruginosa and 1016 DEGs in S. aureus enriched in a variety of biological processes and pathways were identified, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the DEGs were primarily involved in P. aeruginosa two-component system, biofilm formation, and flagellar assembly and in S. aureus biosynthesis of secondary metabolites, microbial metabolism in diverse environments, and biosynthesis of amino acids, respectively. The transcriptional data were validated using quantitative real-time polymerase chain reaction (RT-qPCR), and the expression profiles of 22 major genes remained consistent. These findings suggested that DNase I may inhibit early biofilm formation by downregulating the expression of P. aeruginosa genes associated with flagellar assembly and the type VI secretion system, and by downregulating S. aureus capsular polysaccharide and amino acids metabolism gene expression, respectively. This study offers insights into the mechanisms of DNase treatment-based inhibition of early P. aeruginosa and S. aureus biofilm formation.

Oxidative stress responses in biofilms

Oxidizing agents are low-molecular-weight molecules that oxidize other substances by accepting electrons from them. They include reactive oxygen species (ROS), such as superoxide anions (O2-), hydrogen peroxide (H2O2), and hydroxyl radicals (HO-), and reactive chlorine species (RCS) including sodium hypochlorite (NaOCl) and its active ingredient hypochlorous acid (HOCl), and chloramines. Bacteria encounter oxidizing agents in many different environments and from diverse sources. Among them, they can be produced endogenously by aerobic respiration or exogenously by the use of disinfectants and cleaning agents, as well as by the mammalian immune system. Furthermore, human activities like industrial effluent pollution, agricultural runoff, and environmental activities like volcanic eruptions and photosynthesis are also sources of oxidants. Despite their antimicrobial effects, bacteria have developed many mechanisms to resist the damage caused by these toxic molecules. Previous research has demonstrated that growing as a biofilm particularly enhances bacterial survival against oxidizing agents. This review aims to summarize the current knowledge on the resistance mechanisms employed by bacterial biofilms against ROS and RCS, focussing on the most important mechanisms, including the formation of biofilms in response to oxidative stressors, the biofilm matrix as a protective barrier, the importance of detoxifying enzymes, and increased protection within multi-species biofilm communities. Understanding the complexity of bacterial responses against oxidative stress will provide valuable insights for potential therapeutic interventions and biofilm control strategies in diverse bacterial species.

Proteus mirabilis biofilm expansion microscopy yields over 4-fold magnification for super-resolution of biofilm structure and subcellular DNA organization

Bacterial biofilms form when bacteria attach to surfaces and generate an extracellular matrix that embeds and stabilizes a growing community. Detailed visualization and quantitative analysis of biofilm architecture by optical microscopy are limited by the law of diffraction. Expansion Microscopy (ExM) is a novel Super-Resolution technique where specimens are physically enlarged by a factor of ∼4, prior to observation by conventional fluorescence microscopy. ExM requires homogenization of rigid constituents of biological components by enzymatic digestion. We developed an ExM approach capable of expanding 48-h old Proteus mirabilis biofilms 4.3-fold (termed PmbExM), close to the theoretic maximum expansion factor without gross shape distortions. Our protocol, based on lytic and glycoside-hydrolase enzymatic treatments, degrades rigid components in bacteria and extracellular matrix. Our results prove PmbExM to be a versatile and easy-to-use Super-Resolution approach for enabling studies of P. mirabilis biofilm architecture, assembly, and even intracellular features, such as DNA organization.

Near-infrared laser-assisted Ag@Chi-PB nanocompounds for synergistically eradicating multidrug-resistant bacteria and promoting diabetic abscess healing

Chronic wound infections, particularly multidrug-resistant microbe-caused infections, have imposed severe challenges in clinical administration. The therapeutic effectiveness of the current strategy using conventional antibiotics is extremely unsatisfactory. The development of novel treatment strategies to inhibit the infections caused by multidrug-resistant bacteria is highly desired. In this work, based on the combination of nanocompounds with the assistance of NIR laser, an antibacterial strategy was designed for MRSA-infected abscesses in diabetic mice. The nanocompounds named Ag@Chi-PB were prepared by using chitosan-coated Prussian blue (PB) as a nanocarrier for silver nanoparticles anchoring. Combined with near-infrared (NIR) laser, the nanocompounds were more efficient at killing Escherichia coli (E. coli) and Methicillin-resistant staphyllococcus aureus (MRSA) in vitro. Notably, MRSA was significantly removed in vivo and promoted diabetic abscess healing by the combined therapy of this nanocompound and NIR laser, owing to the synergistic antibacterial effect of photothermal therapy and release of Ag+. Meanwhile, the nanocompound showed satisfactory biocompatibility and superior biosafety. Collectively, the combination therapy of this nanocompound with the assistance of NIR laser may represent a promising strategy for clinical anti-infection.

Metabolic insights from mass spectrometry imaging of biofilms: A perspective from model microorganisms

Biofilms are dense aggregates of bacterial colonies embedded inside a self-produced polymeric matrix. Biofilms have received increasing attention in medical, industrial, and environmental settings due to their enhanced survival. Their characterization using microscopy techniques has revealed the presence of structural and cellular heterogeneity in many bacterial systems. However, these techniques provide limited chemical detail and lack information about the molecules important for bacterial communication and virulence. Mass spectrometry imaging (MSI) bridges the gap by generating spatial chemical information with unmatched chemical detail, making it an irreplaceable analytical platform in the multi-modal imaging of biofilms. In the last two decades, over 30 species of biofilm-forming bacteria have been studied using MSI in different environments. The literature conveys both analytical advancements and an improved understanding of the effects of environmental variables such as host surface characteristics, antibiotics, and other species of microorganisms on biofilms. This review summarizes the insights from frequently studied model microorganisms. We share a detailed list of organism-wide metabolites, commonly observed mass spectral adducts, culture conditions, strains of bacteria, substrate, broad problem definition, and details of the MS instrumentation, such as ionization sources and matrix, to facilitate future studies. We also compared the spatial characteristics of the secretome under different study designs to highlight changes because of various environmental influences. In addition, we highlight the current limitations of MSI in relation to biofilm characterization to enable cross-comparison between experiments. Overall, MSI has emerged to become an important approach for the spatial/chemical characterization of bacterial biofilms and its use will continue to grow as MSI becomes more accessible.

Gene expression reprogramming of Pseudomonas alloputida in response to arginine through the transcriptional regulator ArgR

Different bacteria change their life styles in response to specific amino acids. In Pseudomonas putida (now alloputida) KT2440, arginine acts both as an environmental and a metabolic indicator that modulates the turnover of the intracellular second messenger c-di-GMP, and expression of biofilm-related genes. The transcriptional regulator ArgR, belonging to the AraC/XylS family, is key for the physiological reprogramming in response to arginine, as it controls transport and metabolism of the amino acid. To further expand our knowledge on the roles of ArgR, a global transcriptomic analysis of KT2440 and a null argR mutant growing in the presence of arginine was carried out. Results indicate that this transcriptional regulator influences a variety of cellular functions beyond arginine metabolism and transport, thus widening its regulatory role. ArgR acts as positive or negative modulator of the expression of several metabolic routes and transport systems, respiratory chain and stress response elements, as well as biofilm-related functions. The partial overlap between the ArgR regulon and those corresponding to the global regulators RoxR and ANR is also discussed.

A trinuclear Zn (II) schiff base dicyanamide complex attenuates bacterial biofilm formation by ROS generation and membrane damage and exhibits anticancer activity

A trinuclear Zn (II) complex, [(ZnL{N(CN)2})2Zn], termed complex 1 has been synthesized by the reaction of an aqueous solution of sodium dicyanamide to the methanolic solution of Zn (CH3COO)2, 2H2O and corresponding Schiff base (H2L) which is derived from 1:2 condensation of 1, 4 butane diamine with 3-ethoxy salicylaldehyde. Complex 1 is characterized by elemental analysis, IR, UV and Single X-ray diffraction study. Drug resistance is a growing global public health concern that has prompted researchers to look into advanced alternative treatment modalities. In this context, complex 1 has shown promising antibacterial and antibiofilm efficacy against gram-positive Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus strains. Complex 1 attenuated Staphylococcal biofilm formation by reducing several virulence factors including the formation of extracellular polysaccharide matrix, slime, haemolysin, staphyloxanthin, auto-aggregation, cell surface hydrophobicity, and motility. Notably, complex 1 mechanistically potentiated Reactive Oxygen Species (ROS) generation within the bacterial cells, leading to the damage of bacterial cell membrane followed by DNA leakage and thereby impeding the growth of Staphylococcus aureus. Furthermore, complex 1 significantly exhibited anticancer activity by reducing the growth of prostate adenocarcinoma cells. It obstructed the migration of cancer cells by potentiating apoptosis and arresting the cell cycle at the G2/M phase. In summary, complex 1 could act as a potent candidate for the generation of novel antibacterial, antibiofilm as well as anticancer treatment regimens for the management of drug-resistant biofilm-mediated Staphylococcus aureus infection and lethal prostate malignancy.

Efflux pumps as potential targets for biofilm inhibition

Biofilms account for a great deal of infectious diseases and contribute significantly to antimicrobial resistance. Efflux pumps confer antimicrobial resistance to microorganisms and involve multiple processes of biofilm formation. Efflux pump inhibitors (EPIs) are attracting considerable attention as a biofilm inhibition strategy. The regulatory functions of efflux pumps in biofilm formation such as mediating adherence, quorum sensing (QS) systems, and the expression of biofilm-associated genes have been increasingly identified. The versatile properties confer efflux pumps both positive and negative effects on biofilm formation. Furthermore, the expression and function of efflux pumps in biofilm formation are species-specific. Therefore, this review aims to detail the double-edged sword role of efflux pumps in biofilm formation to provide potential inhibition targets and give an overview of the effects of EPIs on biofilm formation.

Genomic analysis of Ralstonia pickettii reveals the genetic features for potential pathogenicity and adaptive evolution in drinking water

Ralstonia pickettii, the most critical clinical pathogen of the genus Ralstonia, has been identified as a causative agent of numerous harmful infections. Additionally, Ralstonia pickettii demonstrates adaptability to extreme environmental conditions, such as those found in drinking water. In this study, we conducted a comprehensive genomic analysis to investigate the genomic characteristics related to potential pathogenicity and adaptive evolution in drinking water environments of Ralstonia pickettii. Through phylogenetic analysis and population genetic analysis, we divided Ralstonia pickettii into five Groups, two of which were associated with drinking water environments. The open pan-genome with a large and flexible gene repertoire indicated a high genetic plasticity. Significant differences in functional enrichment were observed between the core- and pan-genome of different groups. Diverse mobile genetic elements (MGEs), extensive genomic rearrangements, and horizontal gene transfer (HGT) events played a crucial role in generating genetic diversity. In drinking water environments, Ralstonia pickettii exhibited strong adaptability, and the acquisition of specific adaptive genes was potentially facilitated by genomic islands (GIs) and HGT. Furthermore, environmental pressures drove the adaptive evolution of Ralstonia pickettii, leading to the accumulation of unique mutations in key genes. These mutations may have a significant impact on various physiological functions, particularly carbon metabolism and energy metabolism. The presence of virulence-related elements associated with macromolecular secretion systems, virulence factors, and antimicrobial resistance indicated the potential pathogenicity of Ralstonia pickettii, making it capable of causing multiple nosocomial infections. This study provides comprehensive insights into the potential pathogenicity and adaptive evolution of Ralstonia pickettii in drinking water environments from a genomic perspective.

Metal-organic framework-based advanced therapeutic tools for antimicrobial applications

The escalating concern over conventional antibiotic resistance has emphasized the urgency in developing innovative antimicrobial agents. In recent times, metal-organic frameworks (MOFs) have garnered significant attention within the realm of antimicrobial research due to their multifaceted antimicrobial attributes, including the sustained release of intrinsic or exogenous antimicrobial components, chemodynamically catalyzed generation of reactive oxygen species (ROS), and formation of photogenerated ROS. This comprehensive review provides a thorough overview of the synthetic approaches employed in the production of MOF-based materials, elucidating their underlying antimicrobial mechanisms in depth. The focal point lies in elucidating the research advancements across various antimicrobial modalities, encompassing intrinsic component release system, extraneous component release system, auto-catalytical system, and energy conversion system. Additionally, the progress of MOF-based antimicrobial materials in addressing wound infections, osteomyelitis, and periodontitis is meticulously elucidated, culminating in a summary of the challenges and potential opportunities inherent within the realm of antimicrobial applications for MOF-based materials. STATEMENT OF SIGNIFICANCE: Growing concerns about conventional antibiotic resistance emphasized the need for alternative antimicrobial solutions. Metal-organic frameworks (MOFs) have gained significant attention in antimicrobial research due to their diverse attributes like sustained antimicrobial components release, catalytic generation of reactive oxygen species (ROS), and photogenerated ROS. This review covers MOF synthesis and their antimicrobial mechanisms. It explores advancements in intrinsic and extraneous component release, auto-catalysis, and energy conversion systems. The paper also discusses MOF-based materials' progress in addressing wound infections, osteomyelitis, and periodontitis, along with existing challenges and opportunities. Given the lack of related reviews, our findings hold promise for future MOF applications in antibacterial research, making it relevant to your journal's readership.

Evaluation of Therapeutic Efficiency of Stylicin against Vibrio parahaemolyticus Infection in Shrimp Penaeus vannamei through Comparative Proteomic Approach

The shrimp immune system defends and protects against infection by its naturally expressing antimicrobial peptides. Stylicin is a proline-rich anionic antimicrobial peptide (AMP) that exhibits potent antimicrobial activity. In this study, stylicin gene was isolated from Penaeus vannamei, cloned into vector pET-28a ( +), and overexpressed in Escherichia coli SHuffle T7 cells. The protein was purified and tested for its antibiofilm activity against shrimp pathogen Vibrio parahaemolyticus. It was resulted that the recombinant stylicin significantly reduced the biofilm formation of V. parahaemolyticus at a minimum inhibitory concentration (MIC) of 200 µg. Cell aggregation was observed by using scanning electron microscopy and confocal laser scanning microscopy, and it was resulted that stylicin administration significantly affects the cell structure and biofilm density of V. parahaemolyticus. In addition, real-time PCR confirmed the downregulation (p < 0.05) of genes responsible for growth and colonization. The efficacy of stylicin was tested by injecting it into shrimp challenged with V. parahaemolyticus and 7 days after infection, stylicin-treated animals recovered and survived better in both treatments (T2-100 µg stylicin, - 68.8%; T1-50 µg stylicin, 60%) than in control (7%) (p < 0.01). Comparative proteomic and mass spectrometry analysis of shrimp hemolymph resulted that the expressed proteins were involved in cell cycle, signal transduction, immune pathways, and stress-related proteins representing infection and recovery, and were significantly different in the stylicin-treated groups. The result of this study suggests that the stylicin can naturally boost immunity and can be used as a choice for treating V. parahaemolyticus infections in shrimp.

DA, Roberts AG, Puri AW. A widespread methylotroph acyl-homoserine lactone synthase produces a new quorum sensing signal that regulates swarming in Methylobacterium fujisawaense

IMPORTANCE

Bacteria known as pink-pigmented facultative methylotrophs colonize many diverse environments on earth, play an important role in the carbon cycle, and in some cases promote plant growth. However, little is known about how these organisms interact with each other and their environment. In this work, we identify one of the chemical signals commonly used by these bacteria and discover that this signal controls swarming motility in the pink-pigmented facultative methylotroph Methylobacterium fujisawaense DSM5686. This work provides new molecular details about interactions between these important bacteria and will help scientists predict these interactions and the group behaviors they regulate from genomic sequencing information.

A new easy method for determination of surface adhesion of phototrophic biofilms

Terrestrial cyanobacteria grow as phototrophic biofilms and offer a wide spectrum of interesting products. For cultivation of phototrophic biofilms different reactor concepts have been developed in the last years. One of the main influencing factors is the surface material and the adhesion strength of the chosen production strain. In this work a flow chamber was developed, in which, in combination with optical coherence tomography and computational fluid dynamics simulation, an easy analysis of adhesion forces between different biofilms and varied surface materials is possible. Hereby, differences between two cyanobacteria strains and two surface materials were shown. With longer cultivation time of biofilms adhesion increased in all experiments. Additionally, the content of extracellular polymeric substances was analyzed and its role in surface adhesion was evaluated. To test the comparability of obtained results from the flow chamber with other methods, analogous experiments were conducted with a rotational rheometer, which proved to be successful. Thus, with the presented flow chamber an easy to implement method for analysis of biofilm adhesion was developed, which can be used in future research for determination of suitable combinations of microorganisms with cultivation surfaces on lab scale in advance of larger processes.

Plasmonic inhibition of bacterial adhesion on gold-decorated mesoporous zirconium oxide thin films

Preventing bacterial development on surfaces is essential to avoid problems caused by biofouling. Surfaces decorated with gold nanoparticles have been shown to thermally kill bacteria under high-intensity NIR illumination. In this study, we evaluated the colonization by E. coli of nanostructured surfaces composed of mesoporous zirconia thin films, both with and without gold nanoparticles embedded into the pores. We studied the effect of the nanostructure and of low intensity visible light excitation of the gold nanoparticles on the colonization process. We found that neither the zirconia, nor the presence of pores, or even gold nanoparticles affect bacterial adhesion compared to the bare glass substrate. Therefore, mesoporous zirconia thin films are biologically inert scaffolds that enable the construction of robust surfaces containing functional nanoparticles that can affect bacterial growth. When the gold containing surfaces are irradiated with light, bacterial adhesion shows a remarkable 96 ± 4% reduction. Our studies revealed that these surfaces affect early colonization steps, prior to biofilm formation, preventing bacterial adhesion without affecting its viability. In contrast to related systems where plasmonic excitation induces membrane damage due to strong local heating, the membrane integrity is preserved, showing that these surfaces have a different working principle.

Advancing biofilm management through nanoformulation strategies: a review of dosage forms and administration routes

Biofilms are complex microbial communities formed by the attachment of bacteria or fungi to surfaces encased in a self-produced polymeric matrix. These biofilms are highly resistant to conventional antimicrobial therapies. The resistance mechanisms exhibited by biofilms include low antibiotic absorption, sluggish replication, adaptive stress response, and the formation of dormant-like phenotypes. The eradication of biofilms requires alternative strategies and approaches. Nanotechnological drug delivery systems allow excellent control over the drug chemistry, surface area, particle size, particle shape, and composition of nanostructures. Nanoformulations can enhance the efficacy of antimicrobial agents by improving their bioavailability, stability, and targeted delivery to the site of infection that helps biofilm eradication more effectively. In addition to nanoformulations, the route of administration and choice of dosage forms play a crucial role in treating biofilm infections. Systemic administration of antibiotics is effective in controlling systemic infection and sepsis associated with biofilms. Alternative routes of administration, such as inhalation, vaginal, ocular, or dermal, have been explored to target biofilm infections in specific organs. This review primarily examines the utilisation of nanoformulations in various administration routes for biofilm management. It also provides an overview of biofilms, current approaches, and the drawbacks associated with conventional methods.

Spatial exclusion leads to "tug-of-war" ecological dynamics between competing species within microchannels

Competition is ubiquitous in microbial communities, shaping both their spatial and temporal structure and composition. Classical minimal models of competition, such as the Moran model, have been employed in ecology and evolutionary biology to understand the role of fixation and invasion in the maintenance of population diversity. Informed by recent experimental studies of cellular competition in confined spaces, we extend the Moran model to incorporate mechanical interactions between cells that divide within the limited space of a one-dimensional open microchannel. The model characterizes the skewed collective growth of the cells dividing within the channel, causing cells to be expelled at the channel ends. The results of this spatial exclusion model differ significantly from those of its classical well-mixed counterpart. The mean time to fixation of a species is greatly accelerated, scaling logarithmically, rather than algebraically, with the system size, and fixation/extinction probability sharply depends on the species' initial fractional abundance. By contrast, successful takeovers by invasive species, whether through mutation or immigration, are substantially less likely than in the Moran model. We also find that the spatial exclusion tends to attenuate the effects of fitness differences on the fixation times and probabilities. We find that these effects arise from the combination of the quasi-neutral "tug-of-war" diffusion dynamics of the inter-species boundary around an unstable equipoise point and the quasi-deterministic avalanche dynamics away from the fixed point. These results, which can be tested in microfluidic monolayer devices, have implications for the maintenance of species diversity in dense bacterial and cellular ecosystems where spatial exclusion is central to the competition, such as in organized biofilms or intestinal crypts.

PlzD modifies Vibrio vulnificus foraging behavior and virulence in response to elevated c-di-GMP

IMPORTANCE

Many free-swimming bacteria propel themselves through liquid using rotary flagella, and mounting evidence suggests that the inhibition of flagellar rotation initiates biofilm formation, a sessile lifestyle that is a nearly universal surface colonization paradigm in bacteria. In general, motility and biofilm formation are inversely regulated by the intracellular second messenger bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we identify a protein, PlzD, bearing a conserved c-di-GMP binding PilZ domain that localizes to the flagellar pole in a c-di-GMP-dependent manner and alters the foraging behavior, biofilm, and virulence characteristics of the opportunistic human pathogen, Vibrio vulnificus. Our data suggest that PlzD interacts with components of the flagellar stator to decrease bacterial swimming speed and changes in swimming direction, and these activities are enhanced when cellular c-di-GMP levels are elevated. These results reveal a physical link between a second messenger (c-di-GMP) and an effector (PlzD) that promotes transition from a motile to a sessile state in V. vulnificus.

Consolidated knowledge-guided computational pipeline for therapeutic intervention against bacterial biofilms - a review

Biofilm-associated bacterial infections attributed to multifactorial antimicrobial resistance have caused worldwide challenges in formulating successful treatment strategies. In search of accelerated yet cost-effective therapeutics, several researchers have opted for bioinformatics-based protocols to systemize targeted therapies against biofilm-producing strains. The present review investigated the up-to-date computational databases and servers dedicated to anti-biofilm research to design/screen novel biofilm inhibitors (antimicrobial peptides/phytocompounds/synthetic compounds) and predict their biofilm-inhibition efficacy. Scrutinizing the contemporary in silico methods, a consolidated approach has been highlighted, referred to as a knowledge-guided computational pipeline for biofilm-targeted therapy. The proposed pipeline has amalgamated prominently employed methodologies in genomics, transcriptomics, interactomics and proteomics to identify potential target proteins and their complementary anti-biofilm compounds for effective functional inhibition of biofilm-linked pathways. This review can pave the way for new portals to formulate successful therapeutic interventions against biofilm-producing pathogens.

Predatory bacteria as potential biofilm control and eradication agents in the food industry

Biofilms are a major concern within the food industry since they have the potential to reduce productivity in situ (within the field), impact food stability and storage, and cause downstream food poisoning. Within this review, predatory bacteria as potential biofilm control and eradication agents are discussed, with a particular emphasis on the intraperiplasmic Bdellovibrio-and-like organism (BALO) grouping. After providing a brief overview of predatory bacteria and their activities, focus is given to how BALOs fulfill four attributes that are essential for biocontrol agents to be successful in the food industry: (1) Broad spectrum activity against pathogens, both plant and human; (2) Activity against biofilms; (3) Safety towards humans and animals; and (4) Compatibility with food. As predatory bacteria possess all of these characteristics, they represent a novel form of biofilm biocontrol that is ripe for use within the food industry.

Enhanced bacterial adhesion force by rifampicin resistance promotes microbial colonization on PE plastic compared to non-resistant biofilm formation

The microbial biofilm formed on plastics, is ubiquitous in the environment. However, the effects of antibiotic resistance on the development of the biofilm on plastics, especially with regard to initial cell attachment, remain unclear. In this study, we investigated the initial bacterial adhesion and subsequent biofilm growth of a rifampin (Rif) resistant E. coli (RRE) and a normal gram-positive B. subtilis on a typical plastic (polyethylene, PE). The experiments were conducted in different antibiotic solutions, including Rif, sulfamethoxazole (SMX), and kanamycin (KM), with concentrations ranging from 1 to 1000 μg/L to simulate different aquatic environments. The AFM-based single-cell adhesion force determination revealed that Rif resistance strengthened the adhesion force of RRE to PE in the environment rich in Rif rather than SMX and KM. The enhanced adhesion force may be due to the higher secretion of extracellular polymeric substances (EPS), particularly proteins, by RRE in the presence of Rif compared to the other two antibiotics. In addition, the higher ATP level of RRE would facilitate the initial adhesion and subsequent biofilm growth. Transcriptome analysis of RRE separately cultured in Rif and SMX environments demonstrated a clear correlation between the expression of Rif resistance and the augmented bacterial adhesion and cellular activity. Biofilm biomass analysis confirmed the promotion effect of Rif resistance on biofilm growth when compared to non-resistant biofilms, establishing a novel association with the augmentation of microbial adhesion force. Our study highlights concerns related to the dissemination of antibiotic resistance during microbial colonization on plastic that may arise from antibiotic resistance.

Microbe-Anode Interactions: Comparing the impact of genetic and material engineering approaches to improve the performance of microbial electrochemical systems (MES)

Microbial electrochemical systems (MESs) are a highly versatile platform technology with a particular focus on power or energy production. Often, they are used in combination with substrate conversion (e.g., wastewater treatment) and production of value-added compounds via electrode-assisted fermentation. This rapidly evolving field has seen great improvements both technically and biologically, but this interdisciplinarity sometimes hampers overseeing strategies to increase process efficiency. In this review, we first briefly summarize the terminology of the technology and outline the biological background that is essential for understanding and thus improving MES technology. Thereafter, recent research on improvements at the biofilm-electrode interface will be summarized and discussed, distinguishing between biotic and abiotic approaches. The two approaches are then compared, and resulting future directions are discussed. This mini-review therefore provides basic knowledge of MES technology and the underlying microbiology in general and reviews recent improvements at the bacteria-electrode interface.

The role of RNA regulators, quorum sensing and c-di-GMP in bacterial biofilm formation

Biofilms provide an ecological advantage against many environmental stressors, such as pH and temperature, making it the most common life-cycle stage for many bacteria. These protective characteristics make eradication of bacterial biofilms challenging. This is especially true in the health sector where biofilm formation on hospital or patient equipment, such as respirators, or catheters, can quickly become a source of anti-microbial resistant strains. Biofilms are complex structures encased in a self-produced polymeric matrix containing numerous components such as polysaccharides, proteins, signalling molecules, extracellular DNA and extracellular RNA. Biofilm formation is tightly controlled by several regulators, including quorum sensing (QS), cyclic diguanylate (c-di-GMP) and small non-coding RNAs (sRNAs). These three regulators in particular are fundamental in all stages of biofilm formation; in addition, their pathways overlap, and the significance of their role is strain-dependent. Currently, ribonucleases are also of interest for their potential role as biofilm regulators, and their relationships with QS, c-di-GMP and sRNAs have been investigated. This review article will focus on these four biofilm regulators (ribonucleases, QS, c-di-GMP and sRNAs) and the relationships between them.

CRISPR-Cas system as a promising player against bacterial infection and antibiotic resistance

The phenomenon of antibiotic resistance (AR) and its increasing global trends and destructive waves concerns patients and the healthcare system. In order to combat AR, it is necessary to explore new strategies when the current antibiotics fail to be effective. Thus, knowing the resistance mechanisms and appropriate diagnosis of bacterial infections may help enhance the sensitivity and specificity of novel strategies. On the other hand, resistance to antimicrobial compounds can spread from resistant populations to susceptible ones. Antimicrobial resistance genes (ARGs) significantly disseminate AR via horizontal and vertical gene transfer. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system is a member of the bacterial immune system with the ability to remove the ARGs; therefore, it can be introduced as an effective and innovative strategy in the battle against AR. Here, we reviewed CRISPR-based bacterial diagnosis technologies. Moreover, the strategies to battle AR based on targeting bacterial chromosomes and resistance plasmids using the CRISPR-Cas system have been explained. Besides, we have presented the limitations of CRISPR delivery and potential solutions to help improve the future development of CRISPR-based platforms.

Genomic insights into the c-di-GMP signaling and biofilm development in the saprophytic spirochete Leptospira biflexa

C-di-GMP is a bacterial second messenger with central role in biofilm formation. Spirochete bacteria from Leptospira genus present a wide diversity, with species of medical importance and environmental species, named as saprophytic. Leptospira form biofilms in the rat's reservoir kidneys and in the environment. Here, we performed genomic analyses to identify enzymatic and effector c-di-GMP proteins in the saprophytic biofilm-forming species Leptospira biflexa serovar Patoc. We identified 40 proteins through local alignments. Amongst them, 16 proteins are potentially functional diguanylate cyclases, phosphodiesterases, or hybrid proteins. We also identified nine effectors, including PilZ proteins. Enrichment analyses suggested that c-di-GMP interacts with cAMP signaling system, CsrA system, and flagella assembly regulation during biofilm development of L. biflexa. Finally, we identified eight proteins in the pathogen Leptospira interrogans serovar Copenhageni that share high similarity with L. biflexa c-di-GMP-related proteins. This work revealed proteins related to c-di-GMP turnover and cellular response in Leptospira and their potential roles during biofilm development.

The Role of Biofilms in the Pathogenesis of Animal Bacterial Infections

Biofilms are bacterial aggregates embedded in a self-produced, protective matrix. The biofilm lifestyle offers resilience to external threats such as the immune system, antimicrobials, and other treatments. It is therefore not surprising that biofilms have been observed to be present in a number of bacterial infections. This review describes biofilm-associated bacterial infections in most body systems of husbandry animals, including fish, as well as in sport and companion animals. The biofilms have been observed in the auditory, cardiovascular, central nervous, digestive, integumentary, reproductive, respiratory, urinary, and visual system. A number of potential roles that biofilms can play in disease pathogenesis are also described. Biofilms can induce or regulate local inflammation. For some bacterial species, biofilms appear to facilitate intracellular invasion. Biofilms can also obstruct the healing process by acting as a physical barrier. The long-term protection of bacteria in biofilms can contribute to chronic subclinical infections, Furthermore, a biofilm already present may be used by other pathogens to avoid elimination by the immune system. This review shows the importance of acknowledging the role of biofilms in animal bacterial infections, as this influences both diagnostic procedures and treatment.

Virtual Screening and In Vitro Experimental Verification of LuxS Inhibitors for Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli O157:H7 is an important foodborne pathogen that forms biofilms. In this study, three quorum-sensing (QS) inhibitors (M414-3326, 3254-3286, and L413-0180) were obtained through virtual screening, and their in vitro antibiofilm activities were validated. Briefly, the three-dimensional structure model of LuxS was constructed and characterized using the SWISS-MODEL. High-affinity inhibitors were screened from the ChemDiv database (1,535,478 compounds) using LuxS as a ligand. Five compounds (L449-1159, L368-0079, M414-3326, 3254-3286, and L413-0180) with a good inhibitory effect (50% inhibitory concentration <10 μM) on type II QS signal molecule autoinducer-2 (AI-2) were obtained using a AI-2 bioluminescence assay. The absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties predicated that the five compounds had high intestinal absorption levels (high) and plasma protein binding (absorbent strong) and did not inhibit the metabolism of CYP2D6 metabolic enzymes. In addition, molecular dynamics simulation showed that compounds L449-1159 and L368-0079 could not stably bind with LuxS. Thus, these compounds were excluded. Furthermore, surface plasmon resonance results showed that the three compounds could specifically bind to LuxS. IN addition, the three compounds could effectively inhibit the biofilm formation without affecting the growth and metabolism of the bacteria. Finally, the reverse transcription-quantitative PCR results showed that the three compounds downregulated the expression of the LuxS gene. Overall, these results revealed that the three compounds obtained through virtual screening could inhibit biofilm formation of E. coli O157:H7 and are potential LuxS inhibitors that can be used to treat E. coli O157:H7 infections. IMPORTANCE E. coli O157:H7 is a foodborne pathogen of public health importance. Quorum sensing (QS) is a form of bacterial communication that can regulate various group behaviors, including biofilm formation. Here, we identified three QS AI-2 inhibitors (M414-3326, 3254-3286, and L413-0180) that can stably and specifically bind to LuxS protein. The three QS AI-2 inhibitors inhibited biofilm formation without affecting the growth and metabolic activity of E. coli O157:H7. The three QS AI-2 inhibitors are promising agents for treating E. coli O157:H7 infections. Further studies to identify the mechanism of the three QS AI-2 inhibitors are needed to develop new drugs to overcome antibiotic resistance.

Predictive Molecular Design and Structure-Property Validation of Novel Terpene-Based, Sustainably Sourced Bacterial Biofilm-Resistant Materials

Presented in this work is the use of a molecular descriptor, termed the α parameter, to aid in the design of a series of novel, terpene-based, and sustainable polymers that were resistant to biofilm formation by the model bacterial pathogen Pseudomonas aeruginosa. To achieve this, the potential of a range of recently reported, terpene-derived monomers to deliver biofilm resistance when polymerized was both predicted and ranked by the application of the α parameter to key features in their molecular structures. These monomers were derived from commercially available terpenes (i.e., α-pinene, β-pinene, and carvone), and the prediction of the biofilm resistance properties of the resultant novel (meth)acrylate polymers was confirmed using a combination of high-throughput polymerization screening (in a microarray format) and in vitro testing. Furthermore, monomers, which both exhibited the highest predicted biofilm anti-biofilm behavior and required less than two synthetic stages to be generated, were scaled-up and successfully printed using an inkjet "valve-based" 3D printer. Also, these materials were used to produce polymeric surfactants that were successfully used in microfluidic processing to create microparticles that possessed bio-instructive surfaces. As part of the up-scaling process, a novel rearrangement was observed in a proposed single-step synthesis of α-terpinyl methacrylate via methacryloxylation, which resulted in isolation of an isobornyl-bornyl methacrylate monomer mixture, and the resultant copolymer was also shown to be bacterial attachment-resistant. As there has been great interest in the current literature upon the adoption of these novel terpene-based polymers as green replacements for petrochemical-derived plastics, these observations have significant potential to produce new bio-resistant coatings, packaging materials, fibers, medical devices, etc.

Regulation of biofilm formation in Zymomonas mobilis to enhance stress tolerance by heterologous expression of pfs and luxS

Zymomonas mobilis is a potential alternative of Saccharomyces cerevisiae to produce cellulosic ethanol with strengths in cofactor balance, but its lower tolerance to inhibitors in the lignocellulosic hydrolysate restricts the application. Although biofilm can improve bacteria stress tolerance, regulating biofilm formation in Z. mobilis is still a challenge. In this work, we constructed a pathway by heterologous expressing pfs and luxS from Escherichia coli in Z. mobilis to produce AI-2 (autoinducer 2), a universal quorum-sensing signal molecule, to control cell morphology for enhancing stress tolerance. Unexpectedly, the results suggested that neither endogenous AI-2 nor exogenous AI-2 promoted biofilm formation, while heterologous expression of pfs can significantly raise biofilm. Therefore, we proposed that the main factor in assisting biofilm formation was the product accumulated due to heterologous expression of pfs, like methylated DNA. Consequently, ZM4::pfs produced more biofilm, which presented an enhanced tolerance to acetic acid. All these findings provide a novel strategy to improve the stress tolerance of Z. mobilis by enhancing biofilm formation for efficient production of lignocellulosic ethanol and other value-added chemical products.

Using visible light to activate antiviral and antimicrobial properties of TiO2 nanoparticles in paints and coatings: focus on new developments for frequent-touch surfaces in hospitals

The COVID-19 pandemic refocused scientists the world over to produce technologies that will be able to prevent the spread of such diseases in the future. One area that deservedly receives much attention is the disinfection of health facilities like hospitals, public areas like bathrooms and train stations, and cleaning areas in the food industry. Microorganisms and viruses can attach to and survive on surfaces for a long time in most cases, increasing the risk for infection. One of the most attractive disinfection methods is paints and coatings containing nanoparticles that act as photocatalysts. Of these, titanium dioxide is appealing due to its low cost and photoreactivity. However, on its own, it can only be activated under high-energy UV light due to the high band gap and fast recombination of photogenerated species. The ideal material or coating should be activated under artificial light conditions to impact indoor areas, especially considering wall paints or frequent-touch areas like door handles and elevator buttons. By introducing dopants to TiO₂ NPs, the bandgap can be lowered to a state of visible-light photocatalysis occurring. Naturally, many researchers are exploring this property now. This review article highlights the most recent advancements and research on visible-light activation of TiO₂-doped NPs in coatings and paints. The progress in fighting air pollution and personal protective equipment is also briefly discussed.

Graphical Abstract

Indoor visible-light photocatalytic activation of reactive oxygen species (ROS) over TiO₂ nanoparticles in paint to kill bacteria and coat frequently touched surfaces in the medical and food industries.