Glutathione-Disrupted Biofilms of Clinical Pseudomonas aeruginosa Strains Exhibit an Enhanced Antibiotic Effect and a Novel Biofilm Transcriptome

Antibiofilm Agents for the Treatment and Prevention of Bacterial Vaginosis: A Systematic Narrative Review

BACKGROUND

Bacterial vaginosis (BV) is difficult to eradicate due to BV biofilms protecting BV bacteria (Gardnerella, Prevotella, and other genera). With the growing understanding of biofilms, we systematically reviewed the current knowledge on the efficacy of anti-BV biofilm agents.

METHODS

We searched literature in the Scopus, Medline, and Embase databases for empirical studies investigating substances for the treatment of BV biofilms or prevention of their recurrence and their efficacy and/or safety.

RESULTS

Of 201 unique titles, 35 satisfied the inclusion criteria. Most studies (89%) reported on preclinical laboratory research on the efficacy of experimental antibiofilm agents (80%) rather than their safety. Over 50% were published within the past 5 years. Agents were classified into 7 groups: antibiotics, antiseptics, cationic peptides, enzymes, plant extracts, probiotics, and surfactants/surfactant components. Enzymes and probiotics were most commonly investigated. Earlier reports of antibiotics having anti-BV biofilm activity have not been confirmed. Some compounds from other classes demonstrated promising anti-BV biofilm efficacy in early studies.

CONCLUSIONS

Further research is anticipated on successful antibiofilm agents. If confirmed as effective and safe in human clinical trials, they may offer a breakthrough in BV treatment. With rising antibiotic resistance, antibiofilm agents will significantly improve the current standard of care for BV management.

The Guardian of Vision: Intelligent Bacteriophage-Based Eyedrops for Clinical Multidrug-Resistant Ocular Surface Infections

Clinical multidrug-resistant Pseudomonas aeruginosa (MDR-PA) is the leading cause of refractory bacterial keratitis (BK). However, the reported BK treatment methods lack biosecurity and bioavailability, which usually causes irreversible visual impairment and even blindness. Herein, for BK caused by clinically isolated MDR-PA infection, armed phages are modularized with the type I photosensitizer (PS) ACR-DMT, and an intelligent phage eyedrop is developed for combined phagotherapy and photodynamic therapy (PDT). These eyedrops maximize the advantages of bacteriophages and ACR-DMT, enabling more robust and specific targeting killing of MDR-PA under low oxygen-dependence, penetrating and disrupting biofilms, and efficiently preventing biofilm reformation. Altering the biofilm and immune microenvironments alleviates inflammation noninvasively, promotes corneal healing without scar formation, protects ocular tissues, restores visual function, and prevents long-term discomfort and pain. This strategy exhibits strong scalability, enables at-home treatment of ocular surface infections with great patient compliance and a favorable prognosis, and has significant potential for clinical application.

Identification and characterization of TatD DNase in planarian Dugesia japonica and its antibiofilm effect

TatD DNase, a key enzyme in vertebrates and invertebrates, plays a pivotal role in various physiological processes. Dugesia japonica (D. japonica), a flatworm species, has remarkable regenerative capabilities and possesses a simplified immune system. However, the existence and biological functions of TatD DNase in D. japonica require further investigation. Here, we obtained the open reading frame (ORF) of DjTatD and demonstrated its conservation. The three-dimensional structure of DjTatD revealed its active site and binding mechanism. To investigate its enzymological properties, we overexpressed, purified, and characterized recombinant DjTatD (rDjTatD). We observed that DjTatD was primarily expressed in the pharynx and its expression could be significantly challenged upon stimulation with lipopolysaccharide, peptidoglycan, gram-positive and gram-negative bacteria. RNA interference results indicated that both DjTatD and DjDN2s play a role in pharyngeal regeneration and may serve as functional complements to each other. Additionally, we found that rDjTatD and recombinant T7DjTatD effectively reduce biofilm formation regardless of their bacterial origin. Together, our results demonstrated that DjTatD may be involved in the planarian immune response and pharyngeal regeneration. Furthermore, after further optimization in the future, rDjTatD and T7DjTatD can be considered highly effective antibiofilm agents.

Enhanced Chemoradiotherapy for MRSA-Infected Osteomyelitis Using Immunomodulatory Polymer-Reinforced Nanotherapeutics

The eradication of osteomyelitis caused by methicillin-resistant Staphylococcus aureus (MRSA) poses a significant challenge due to its development of biofilm-induced antibiotic resistance and impaired innate immunity, which often leads to frequent surgical failure. Here, the design, synthesis, and performance of X-ray-activated polymer-reinforced nanotherapeutics that modulate the immunological properties of infectious microenvironments to enhance chemoradiotherapy against multidrug-resistant bacterial deep-tissue infections are reported. Upon X-ray radiation, the proposed polymer-reinforced nanotherapeutic generates reactive oxygen species and reactive nitrogen species. To robustly eradicate MRSA biofilms at deep infection sites, these species can specifically bind to MRSA and penetrate biofilms for enhanced chemoradiotherapy treatment. X-ray-activated nanotherapeutics modulate the innate immunity of macrophages to prevent the recurrence of osteomyelitis. The remarkable anti-infection effects of these nanotherapeutics are validated using a rat osteomyelitis model. This study demonstrates the significant potential of a synergistic chemoradiotherapy and immunotherapy method for treating MRSA biofilm-infected osteomyelitis.

Iron-Single-Atom Nanozyme with NIR Enhanced Catalytic Activities for Facilitating MRSA-Infected Wound Therapy

Patients with methicillin-resistant Staphylococcus aureus (MRSA) infections may have higher death rates than those with non-drug-resistant infections. Nanozymes offer a promising approach to eliminating bacteria by producing reactive oxygen species. However, most of the conventional nanozyme technologies encounter significant challenges with respect to size, composition, and a naturally low number of active sites. The present study synthesizes a iron-single-atom structure (Fe-SAC) via nitrogen doped-carbon, a Fe-N5 catalyst (Fe-SAC) with a high metal loading (4.3 wt.%). This catalyst permits the development of nanozymes consisting of single-atom structures with active sites resembling enzymes, embedded within nanomaterials. Fe-SAC displays peroxidase-like activities upon exposure to H2O2. This structure facilitates the production of hydroxyl radicals, well-known for their strong bactericidal effects. Furthermore, the photothermal properties augment the bactericidal efficacy of Fe-SAC. The findings reveal that Fe-SAC disrupts the bacterial cell membranes and the biofilms, contributing to their antibacterial effects. The bactericidal properties of Fe-SAC are harnessed, which eradicates the MRSA infections in wounds and improves wound healing. Taken together, these findings suggest that single Fe atom nanozymes offer a novel perspective on the catalytic mechanism and design, holding immense potential as next-generation nanozymes.

Copper incorporated biomaterial-based technologies for multifunctional wound repair

The treatment of wounds is a worldwide challenge, and wound infection can affect the effectiveness of wound treatment and further increase the disease burden. Copper is an essential trace element that has been shown to have broad-spectrum antibacterial effects and to be involved in the inflammation, proliferation, and remodeling stages of wound healing. Compared to treatments such as bioactive factors and skin grafts, copper has the advantage of being low-cost and easily available, and has received a lot of attention in wound healing. Recently, biomaterials made by incorporating copper into bioactive glasses, polymeric scaffolds and hydrogels have been used to promote wound healing by the release of copper ions. In addition, copper-incorporated biomaterials with catalytic, photothermal, and photosensitive properties can also accelerate wound healing through antibacterial and wound microenvironment regulation. This review summarizes the antibacterial mechanisms of copper- incorporated biomaterials and their roles in wound healing, and discusses the current challenges. A comprehensive understanding of the role of copper in wounds will help to facilitate new preclinical and clinical studies, thus leading to the development of novel therapeutic tools.

Exogenous glutathione reverses meropenem resistance in carbapenem-resistant Klebsiella pneumoniae

Background: The rate of carbapenem-resistant Klebsiella pneumoniae (CRKP) infection has been increasing rapidly worldwide and, poses a significant risk to human health. Effective methods are urgently needed to address treatment failures related to antibiotic resistance. Recent research has reported that some drugs in combination with antibiotics have displayed synergistic killing of resistant bacteria. Here, we investigated whether glutathione (GSH) can synergize with meropenem, and enhance its effectiveness against CRKP. Methods: Synergistic activity was assessed by checkerboard and time-killing assays. The mechanism of these combinations was assessed by total ROS and membrane permeability assays. The bacterial metabolites were assessed by LC‒MS/MS. Results: The FICIs of GSH and meropenem were approximately 0.5 and the combined treatment with GSH and meropenem resulted in a more than 2log10 CFU/mL reduction in bacteria compared to the individual treatments. These findings indicated the synergistic effect of the two drugs. Moreover, the meropenem MIC of CRKP was reduced to less than 4 mg/L when combined with 6 mg/mL GSH, indicating that GSH could significantly reverse resistance to meropenem in bacteria. The production of ROS in bacteria was determined by flow cytometry. After adding GSH, the ROS in the GSH group and the combined group was significantly higher than that in the control and meropenem groups, but there was no significant difference between the combined and GSH groups. The metabolic disturbance caused by GSH alone and in combination with meropenem was significant intracellularly and extracellularly, especially in terms of glycerophospholipid metabolism, indicating that the synergistic effect of the combined use of GSH and meropenem was relevant to glycerophospholipid metabolism. In addition, we measured the cell membrane permeability. The cell membrane permeability of the combination group was significantly higher than that of the blank control or monotreatment groups. This confirmed that the GSH can serve as a meropenem enhancers by disturbing glycerophospholipid metabolism and increasing cell membrane permeability. Conclusion: GSH and meropenem display a synergistic effect, wherein GSH increases the sensitivity of CRKP to meropenem. The synergy and susceptibility effects are thought to related to the increased membrane permeability resulting from the perturbations in glycerophospholipid metabolism, presenting a novel avenue for CRKP treatment.

Glutamate-pantothenate pathway promotes antibiotic resistance of Edwardsiella tarda

Although cellular metabolic states have been shown to modulate bacterial susceptibility to antibiotics, the interaction between glutamate (Glu) and chloramphenicol (CAP) resistance remains unclear because of the specificity of antibiotics and bacteria. We found that the level of Glu was upregulated in the CAP-resistant strain of Edwardsiella tarda according to a comparative metabolomics approach based on LC-MS/MS. Furthermore, we verified that exogenous metabolites related to Glu, the tricarboxylic acid (TCA) cycle, and glutathione (GSH) metabolism could promote CAP resistance in survival assays. If GSH metabolism or the TCA cycle is inhibited by L-buthionine sulfoximine or propanedioic acid, the promotion of CAP resistance by Glu in the corresponding pathway disappears. According to metabolomic analysis, exogenous Glu could change pantothenate metabolism, affecting GSH biosynthesis and the TCA cycle. These results showed that the glutamate-pantothenate pathway could promote CAP resistance by being involved in the synthesis of GSH, entering the TCA cycle by direct deamination, or indirectly affecting the metabolism of the two pathways by pantothenate. These results extend our knowledge of the effect of Glu on antibiotic resistance and suggest that the potential effect, which may aggravate antibiotic resistance, should be considered before Glu and GSH administration in the clinic.

Synthesis of Antimicrobial Gallium Nanoparticles Using the Hot Injection Method

Antibiotic resistance continues to be an ongoing problem in global public health despite interventions to reduce antibiotic overuse. Furthermore, it threatens to undo the achievements and progress of modern medicine. To address these issues, the development of new alternative treatments is needed. Metallic nanoparticles have become an increasingly attractive alternative due to their unique physicochemical properties that allow for different applications and their various mechanisms of action. In this study, gallium nanoparticles (Ga NPs) were tested against several clinical strains of Pseudomonas aeruginosa (DFU53, 364077, and 365707) and multi-drug-resistant Acinetobacter baumannii (MRAB). The results showed that Ga NPs did not inhibit bacterial growth when tested against the bacterial strains using a broth microdilution assay, but they exhibited effects in biofilm production in P. aeruginosa DFU53. Furthermore, as captured by atomic force microscopy imaging, P. aeruginosa DFU53 and MRAB biofilms underwent morphological changes, appearing rough and irregular when they were treated with Ga NPs. Although Ga NPs did not affect planktonic bacterial growth, their effects on both biofilm formation and established biofilm demonstrate their potential role in the race to combat antibiotic resistance, especially in biofilm-related infections.

Stimuli-Responsive Double Single-Atom Catalysts for Parallel Catalytic Therapy

Tumor microenvironment (TME)-induced nanocatalytic therapy is a trending strategy for tumor-targeting therapy, but the low catalytic efficiency remains to limit its therapeutic effect. The single-atom catalysts (SACs) appear as a novel type of nanozymes that possesses incredible catalytic activity. Here, we developed PEGylated manganese/iron-based SACs (Mn/Fe PSACs) by coordinating single-atom Mn/Fe to nitrogen atoms in hollow zeolitic imidazolate frameworks (ZIFs). Mn/Fe PSACs catalyze cellular hydrogen peroxide (H2O2) converting to hydroxyl radical (•OH) through a Fenton-like reaction; it also enhances the decomposition of H2O2 to O2 that continuously converts to cytotoxic superoxide ion (•O2-) via oxidase-like activity. Mn/Fe PSACs can reduce the depletion of reactive oxygen species (ROS) by consuming glutathione (GSH). Here, we demonstrated the Mn/Fe PSACs-mediated synergistic antitumor efficacy among in vitro and in vivo experiments. This study proposes new promising single-atom nanozymes with highly efficient biocatalytic sites and synergistic therapeutic effects, which will give birth to abundant inspirations in ROS-related biological applications in broad biomedical fields.

Na2S2O4@Co-metal organic framework (ZIF-67) @glucose oxidase for biofilm-infecting wound healing with immune activation

In recent years, photodynamic therapy (PDT) or chemodynamic therapy (CDT) based on the antimicrobial property or anti-biofilm property of reactive oxygen species (ROS) have been widely recognized for their low susceptibility to microbial resistance. However, due to the complication of the three-dimensional structure of the biofilm at the wound site and the high quenching rate of common ROS, the treatment with traditional ROS could not achieve satisfactory wound healing effects. Here, Na₂S₂O₈@ZIF-67/GOx nanoparticles (NZG NPs) were prepared as a new high-toxic ROS nanogenerator for application of biofilm-infecting wound healing with the assistance of glucose oxidase (GOx) for amplified CDT and immune activation. When the NZG NPs entered the biofilm, Co-based metal organic frame (ZIF-67) ruptured in the acidic microenvironment, which induced the release of GOx and the production of gluconic acid and H₂O₂, further promoting the decrease of pH of the biofilm microenvironment and in turn accelerating the cleavage of ZIF-67 and the release of Na₂S₂O₈. Then, S₂O₈^2- could gradually transformed into high-toxic sulfate radical (SO₄^-), part of which further produced OH in situ with H₂O, thereby inhibiting the proliferation of bacteria and biofilms. Interestingly, these two types of ROS not only caused direct damage to the biofilm, but also activated the immune system of the wound site as well as the body more effectively, which also played an indirect role in promoting biofilm destruction and wound healing. In vitro and in vivo results showed that, as a new high-toxic ROS nanogenerator, the NZG NPs supply amplified chemodynamic therapy and immune activation to destroy biofilms, but also achieve effective wound healing without causing bacterial tolerance, which provides a new strategy for the development of biofilm-infecting wound healing.

The Efficacy of an N-Acetylcysteine-Antibiotic Combination Therapy on Achromobacter xylosoxidans in a Cystic Fibrosis Sputum/Lung Cell Model

Cystic fibrosis (CF) is a disorder causing dysfunctional ion transport resulting in the accumulation of viscous mucus. This environment fosters a chronic bacterial biofilm-associated infection in the airways. Achromobacter xylosoxidans, a gram-negative aerobic bacillus, has been increasingly associated with antibiotic resistance and chronic colonisation in CF. In this study, we aimed to create a reproducible model of CF infection using an artificial sputum medium (ASMDM-1) with bronchial (BEAS-2B) and macrophage (THP-1) cells to test A. xylosoxidans infection and treatment toxicity. This study was conducted in three distinct stages. First, the tolerance of BEAS-2B cell lines and two A. xylosoxidans strains against ASMDM-1 was optimised. Secondly, the cytotoxicity of combined therapy (CT) comprising N-acetylcysteine (NAC) and the antibiotics colistin or ciprofloxacin was tested on cells alone in the sputum model in both BEAS-2B and THP-1 cells. Third, the efficacy of CT was assessed in the context of a bacterial infection within the live cell/sputum model. We found that a model using 20% ASMDM-1 in both cell populations tolerated a colistin-NAC-based CT and could significantly reduce bacterial loads in vitro (~2 log10 CFU/mL compared to untreated controls). This pilot study provides the foundation to study other bacterial opportunists that infect the CF lung to observe infection and CT kinetics. This model also acts as a springboard for more complex co-culture models.

The Xanthophyll Carotenoid Lutein Reduces the Invasive Potential of Pseudomonas aeruginosa and Increases Its Susceptibility to Tobramycin

Recently, the xanthophyll carotenoid lutein has been qualified as a potential quorum sensing (QS) and biofilm inhibitor against Pseudomonas aeruginosa. To address the potential of this xanthophyll compound as a relevant antivirulence agent, we investigated in depth its impact on the invasion capabilities and aggressiveness of P. aeruginosa PAO1, which rely on the bacterial ability to build and maintain protective barriers, use different types of motilities and release myriad virulence factors, leading to host cell and tissue damages. Our data, obtained on the PAO1 strain, indicate that all-trans lutein (Lut; 22 µM) disrupts biofilm formation and disorganizes established biofilm structure without affecting bacterial viability, while improving the bactericidal activity of tobramycin against biofilm-encapsulated PAO1 cells. Furthermore, this xanthophyll affects PAO1 twitching and swarming motilities while reducing the production of the extracellular virulence factors pyocyanin, elastase and rhamnolipids as well as the expression of the QS-regulated lasB and rhlA genes without inhibiting the QS-independent aceA gene. Interestingly, the expression of the QS regulators rhlR/I and lasR/I is significantly reduced as well as that of the global virulence factor regulator vfr, which is suggested to be a major target of Lut. Finally, an oxidative metabolite of Lut, 3′-dehydrolutein, induces a similar inhibition phenotype. Taken together, lutein-type compounds represent potential agents to control the invasive ability and antibiotic resistance of P. aeruginosa.

The Use of Artificial Sputum Media to Enhance Investigation and Subsequent Treatment of Cystic Fibrosis Bacterial Infections

In cystic fibrosis (CF), mutations in the CF transmembrane conductance regulator protein reduce ionic exchange in the lung, resulting in thicker mucus, which impairs mucociliary function, airway inflammation and infection. The mucosal and nutritional environment of the CF lung is inadequately mimicked by commercially available growth media, as it lacks key components involved in microbial pathogenesis. Defining the nutritional composition of CF sputum has been a long-term goal of in vitro research into CF infections to better elucidate bacterial growth and infection pathways. This narrative review highlights the development of artificial sputum medium, from a viable in vitro method for understanding bacterial mechanisms utilised in CF lung, to uses in the development of antimicrobial treatment regimens and examination of interactions at the epithelial cell surface and interior by the addition of host cell layers. The authors collated publications based on a PubMed search using the key words: “artificial sputum media” and “cystic fibrosis”. The earliest iteration of artificial sputum media were developed in 1997. Formulations since then have been based either on published data or chemically derived from extracted sputum. Formulations contain combinations of mucin, extracellular DNA, iron, amino acids, and lipids. A valuable advantage of artificial sputum media is the ability to standardise media composition according to experimental requirements.

Pseudomonas aeruginosa Initiates a Rapid and Specific Transcriptional Response during Surface Attachment

Chronic biofilm infections by Pseudomonas aeruginosa are a major contributor to the morbidity and mortality of patients. The formation of multicellular bacterial aggregates, called biofilms, is associated with increased resistance to antimicrobials and immune clearance and the persistence of infections. Biofilm formation is dependent on bacterial cell attachment to surfaces, and therefore, attachment plays a key role in chronic infections. We hypothesized that bacteria sense various surfaces and initiate a rapid, specific response to increase adhesion and establish biofilms. RNA sequencing (RNA-Seq) analysis identified transcriptional changes of adherent cells during initial attachment, identifying the bacterial response to an abiotic surface over a 1-h period. Subsequent screens investigating the most highly regulated genes in surface attachment identified 4 genes, pfpI, phnA, leuD, and moaE, all of which have roles in both metabolism and biofilm formation. In addition, the transcriptional responses to several different medically relevant abiotic surfaces were compared after initial attachment. Surprisingly, there was a specific transcriptional response to each surface, with very few genes being regulated in response to surfaces in general. We identified a set of 20 genes that were differentially expressed across all three surfaces, many of which have metabolic functions, including molybdopterin cofactor biosynthesis and nitrogen metabolism. This study has advanced the understanding of the kinetics and specificity of bacterial transcriptional responses to surfaces and suggests that metabolic cues are important signals during the transition from a planktonic to a biofilm lifestyle.

IMPORTANCE Bacterial biofilms are a significant concern in many aspects of life, including chronic infections of airways, wounds, and indwelling medical devices; biofouling of industrial surfaces relevant for food production and marine surfaces; and nosocomial infections. The effects of understanding surface adhesion could impact many areas of life. This study utilized emerging technology in a novel approach to address a key step in bacterial biofilm development. These findings have elucidated both conserved and surface-specific responses to several disease-relevant abiotic surfaces. Future work will expand on this report to identify mechanisms of biofilm initiation with the aim of identifying bacterial factors that could be targeted to prevent biofilms.

Continuous Production of Human Epidermal Growth Factor Using Escherichia coli Biofilm

Increasing demand for recombinant proteins necessitates efficient protein production processes. In this study, a continuous process for human epidermal growth factor (hEGF) secretion by Escherichia coli was developed by taking advantage of biofilm formation. Genes bcsB, fimH, and csgAcsgB that have proved to facilitate biofilm formation and some genes moaE, yceA, ychJ, and gshB potentially involved in biofilm formation were examined for their effects on hEGF secretion as well as biofilm formation. Finally, biofilm-based fermentation processes were established, which demonstrated the feasibility of continuous production of hEGF with improved efficiency. The best result was obtained from ychJ-disruption that showed a 28% increase in hEGF secretion over the BL21(DE3) wild strain, from 24 to 32 mg/L. Overexpression of bcsB also showed great potential in continuous immobilized fermentation. Overall, the biofilm engineering here represents an effective strategy to improve hEGF production and can be adapted to produce more recombinant proteins in future.

Extracellular degradation of a polyurethane oligomer involving outer membrane vesicles and further insights on the degradation of 2,4-diaminotoluene in Pseudomonas capeferrum TDA1

The continuing reports of plastic pollution in various ecosystems highlight the threat posed by the ever-increasing consumption of synthetic polymers. Therefore, Pseudomonas capeferrum TDA1, a strain recently isolated from a plastic dump site, was examined further regarding its ability to degrade polyurethane (PU) compounds. The previously reported degradation pathway for 2,4-toluene diamine, a precursor and degradation intermediate of PU, could be confirmed by RNA-seq in this organism. In addition, different cell fractions of cells grown on a PU oligomer were tested for extracellular hydrolytic activity using a standard assay. Strikingly, purified outer membrane vesicles (OMV) of P. capeferrum TDA1 grown on a PU oligomer showed higher esterase activity than cell pellets. Hydrolases in the OMV fraction possibly involved in extracellular PU degradation were identified by mass spectrometry. On this basis, we propose a model for extracellular degradation of polyester-based PUs by P. capeferrum TDA1 involving the role of OMVs in synthetic polymer degradation.

Copper single-atom catalysts with photothermal performance and enhanced nanozyme activity for bacteria-infected wound therapy

Nanozymes have become a new generation of antibiotics with exciting broad-spectrum antibacterial properties and negligible biological toxicity. However, their inherent low catalytic activity limits their antibacterial properties. Herein, Cu single-atom sites/N doped porous carbon (Cu SASs/NPC) is successfully constructed for photothermal-catalytic antibacterial treatment by a pyrolysis-etching-adsorption-pyrolysis (PEAP) strategy. Cu SASs/NPC have stronger peroxidase-like catalytic activity, glutathione (GSH)-depleting function, and photothermal property compared with non-Cu-doped NPC, indicating that Cu doping significantly improves the catalytic performance of nanozymes. Cu SASs/NPC can effectively induce peroxidase-like activity in the presence of H2O2, thereby generating a large amount of hydroxyl radicals (•OH), which have a certain killing effect on bacteria and make bacteria more susceptible to temperature. The introduction of near-infrared (NIR) light can generate hyperthermia to fight bacteria, and enhance the peroxidase-like catalytic activity, thereby generating additional •OH to destroy bacteria. Interestingly, Cu SASs/NPC can act as GSH peroxidase (GSH-Px)-like nanozymes, which can deplete GSH in bacteria, thereby significantly improving the sterilization effect. PTT-catalytic synergistic antibacterial strategy produces almost 100% antibacterial efficiency against Escherichia coli (E. coli) and methicillin-resistant Staphylococcus aureus (MRSA). In vivo experiments show a better PTT-catalytic synergistic therapeutic performance on MRSA-infected mouse wounds. Overall, our work highlights the wide antibacterial and anti-infective bio-applications of Cu single-atom-containing catalysts.

Smart Polymeric Delivery System for Antitumor and Antimicrobial Photodynamic Therapy

Photodynamic therapy (PDT) has attracted tremendous attention in the antitumor and antimicrobial areas. To enhance the water solubility of photosensitizers and facilitate their accumulation in the tumor/infection site, polymeric materials are frequently explored as delivery systems, which are expected to show target and controllable activation of photosensitizers. This review introduces the smart polymeric delivery systems for the PDT of tumor and bacterial infections. In particular, strategies that are tumor/bacteria targeted or activatable by the tumor/bacteria microenvironment such as enzyme/pH/reactive oxygen species (ROS) are summarized. The similarities and differences of polymeric delivery systems in antitumor and antimicrobial PDT are compared. Finally, the potential challenges and perspectives of those polymeric delivery systems are discussed.

Current and Emerging Therapies to Combat Cystic Fibrosis Lung Infections

The ultimate aim of any antimicrobial treatment is a better infection outcome for the patient. Here, we review the current state of treatment for bacterial infections in cystic fibrosis (CF) lung while also investigating potential new treatments being developed to see how they may change the dynamics of antimicrobial therapy. Treatment with antibiotics coupled with regular physical therapy has been shown to reduce exacerbations and may eradicate some strains. Therapies such as hypertonic saline and inhaled PulmozymeTM (DNase-I) improve mucus clearance, while modifier drugs, singly and more successfully in combination, re-open certain mutant forms of the cystic fibrosis transmembrane conductance regulator (CFTR) to enable ion passage. No current method, however, completely eradicates infection, mainly due to bacterial survival within biofilm aggregates. Lung transplants increase lifespan, but reinfection is a continuing problem. CFTR modifiers normalise ion transport for the affected mutations, but there is conflicting evidence on bacterial clearance. Emerging treatments combine antibiotics with novel compounds including quorum-sensing inhibitors, antioxidants, and enzymes, or with bacteriophages, aiming to disrupt the biofilm matrix and improve antibiotic access. Other treatments involve bacteriophages that target, infect and kill bacteria. These novel therapeutic approaches are showing good promise in vitro, and a few have made the leap to in vivo testing.

The effect of N-acetylcysteine in a combined antibiofilm treatment against antibiotic-resistant Staphylococcus aureus

BACKGROUND

The WHO declared Staphylococcus aureus as a 'pathogen of high importance' in 2017. One-fifth of all bloodstream-related infections in Australia and 12 000 cases of bacteraemia in the UK (2017-18) were caused by the MRSA variant. To address the need for novel therapies, we investigated several permutations of an innovative combination therapy containing N-acetylcysteine (NAC), an antibiotic and an enzyme of choice in eradicating MRSA and MSSA biofilms.

METHODS

Biofilm viability (resazurin assay) and colony count methods were used to investigate the effect of NAC, antibiotics and enzymes on S. aureus biofilm disruption and killing. The effects of NAC and enzymes on the polysaccharide content of biofilm matrices were analysed using the phenol/sulphuric acid method and the effect of NAC on DNA cleavage was determined using the Qubit fluorometer technique. Changes in biofilm architecture when subjected to NAC and enzymes were visualized using confocal laser scanning microscopy (CLSM).

RESULTS

NAC alone displayed bacteriostatic effects when tested on planktonic bacterial growth. Combination treatments containing 30 mM NAC resulted in ≥90% disruption of biofilms across all MRSA and MSSA strains with a 2-3 log10 decrease in cfu/mL in treated biofilms. CLSM showed that NAC treatment drastically disrupted S. aureus biofilm architecture. There was also reduced polysaccharide production in MRSA biofilms in the presence of NAC.

CONCLUSIONS

Our results indicate that inclusion of NAC in a combination treatment is a promising strategy for S. aureus biofilm eradication. The intrinsic acidity of NAC was identified as key to maximum biofilm disruption and degradation of matrix components.

Pulmonary biofilm-based chronic infections and inhaled treatment strategies

Certain pulmonary diseases, such as cystic fibrosis (CF), non-CF bronchiectasis, chronic obstructive pulmonary disease, and ventilator-associated pneumonia, are usually accompanied by respiratory tract infections due to the physiological alteration of the lung immunological defenses. Recurrent infections may lead to chronic infection through the formation of biofilms. Chronic biofilm-based infections are challenging to treat using antimicrobial agents. Therefore, effective ways to eradicate biofilms and thus relieve respiratory tract infection require the development of efficacious agents for biofilm destruction, the design of delivery carriers with biofilm-targeting and/or penetrating abilities for these agents, and the direct delivery of them into the lung. This review provides an in-depth description of biofilm-based infections caused by pulmonary diseases and focuses on current existing agents that are administered by inhalation into the lung to treat biofilm, which include i) inhalable antimicrobial agents and their combinations, ii) non-antimicrobial adjuvants such as matrix-targeting enzymes, mannitol, glutathione, cyclosporin A, and iii) liposomal formulations of anti-biofilm agents. Finally, novel agents that have shown promise against pulmonary biofilms as well as traditional and new devices for pulmonary delivery of anti-biofilm agents into the lung are also discussed.

New roles for glutathione: Modulators of bacterial virulence and pathogenesis

Low molecular weight (LMW) thiols contain reducing sulfhydryl groups that are important for maintaining antioxidant defense in the cell. Aside from the traditional roles of LMW thiols as redox regulators in bacteria, glutathione (GSH) has been reported to affect virulence and bacterial pathogenesis. The role of GSH in virulence is diverse, including the activation of virulence gene expression and contributing to optimal biofilm formation. GSH can also be converted to hydrogen sulfide (H₂S) which is important for the pathogenesis of certain bacteria. Besides GSH, some bacteria produce other LMW thiols such as mycothiol and bacillithiol that affect bacterial virulence. We discuss these newer reported functions of LMW thiols modulating bacterial pathogenesis either directly or indirectly and via modulation of the host immune system.

Synthesis, Enzymatic Degradation, and Polymer-Miscibility Evaluation of Nonionic Antimicrobial Hyperbranched Polyesters with Indole or Isatin Functionalities

Most macromolecular antimicrobials are ionic and thus lack miscibility/compatibility with nonionic substrate materials. In this context, nonionic hyperbranched polyesters (HBPs) with indole or isatin functionality were rationally designed, synthesized, and characterized. Antimicrobial disk diffusion assay indicated that these HBPs showed significant antibacterial activity against 8 human pathogenic bacteria compared to small molecules with indole or isatin groups. According to DSC measurements, up to 20% indole-based HBP is miscible with biodegradable polyesters (polyhydroxybutyrate or polycaprolactone), which can be attributed to the favorable hydrogen bonding between the N–H moiety of indole and the C=O of polyesters. HBPs with isatin or methylindole were completely immiscible with the same matrices. None of the HBPs leaked out from plastic matrix after being immersed in water for 5 days. The incorporation of indole into HBPs as well as small molecules facilitated their enzymatic degradation with PETase from Ideonella sakaiensis, while isatin had a complex impact. Molecular docking simulations of monomeric molecules with PETase revealed different orientations of the molecules at the active site due to the presence of indole or isatin groups, which could be related to the observed different enzymatic degradation behavior. Finally, biocompatibility analysis with a mammalian cell line showed the negligible cytotoxic effect of the fabricated HBPs.

Quorum sensing systems, related virulence factors, and biofilm formation in Pseudomonas aeruginosa isolated from fish

In this study, two quorum sensing (QS) system genes, las and rhI; N-3-oxo-dodecanoyl homoserine lactone (AHL; 3-O-C₁₂-HSL); and QS-related virulence factors and correlation between them were assessed in 30 fish origin P. aeruginosa isolates. The detection of two QS system of the isolates, and eight gene regions consisting of four intact (lasI/R, rhlI/R) and four internal (lasI/R, rhlI/R) genes were tested by PCR assay. According to findings, las and rhI QS system genes were detected in 27 and 30 isolates, respectively, while 3-O-C₁₂-HSL was determined in 13 isolates. A total of 22, 27, and 18 isolates were capable of pyocyanin production, protease, and elastase activity, respectively. Biofilm formation was detected using three methods in all 30 isolates: 12 by Congo red agar, 14 by microtiter plate, and 29 by tube test. Twitching and swarming motility types were detected in 30, but the swimming motility was determined in 25 isolates. The rhI QS system genes detected in all of the isolates having three types including motility, PYA production, and protease and elastase activities. The las QS system genes were detected in 27 of the motility, 17 of PYA production, 25 of protease, and 16 of elastase activity having isolates. In conclusion, the high number of P. aeruginosa isolates from fish tested have two QS systems and related virulence factors. There was also correlation between them.

A dual-therapy approach for the treatment of biofilm-mediated Salmonella gallbladder carriage

Asymptomatic carriage of Salmonella Typhi continues to facilitate the transmission of typhoid fever, resulting in 14 million new infections and 136,000 fatalities each year. Asymptomatic chronic carriage of S. Typhi is facilitated by the formation of biofilms on gallstones that protect the bacteria from environmental insults and immune system clearance. Here, we identified two unique small molecules capable of both inhibiting Salmonella biofilm growth and disrupting pre-formed biofilm structures without affecting bacterial viability. In a mouse model of chronic gallbladder Salmonella carriage, treatment with either compound reduced bacterial burden in the gallbladder by 1–2 logs resulting in bacterial dissemination to peripheral organs that was associated with increased mortality. Co-administration of either compound with ciprofloxacin not only enhanced compound efficacy in the gallbladder by a further 1–1.5 logs for a total of 3–4.5 log reduction, but also prevented bacterial dissemination to peripheral organs. These data suggest a dual-therapy approach targeting both biofilm and planktonic populations can be further developed as a safe and efficient treatment of biofilm-mediated chronic S. Typhi infections.

Typhoid fever is an infectious disease caused by Salmonella Typhi (S. Typhi), a bacterium that causes as many as 14 million new infections and 136,000 deaths annually. Asymptomatic chronic carriers of S. Typhi play a major role in the transmission of typhoid fever, as they intermittently shed the bacteria and can unknowingly infect surrounding individuals. Here, we characterized novel compounds that target biofilm formation, a process utilized by S. Typhi to establish and maintain chronic carriage in the gallbladder, in hopes that they may be eventually used in conjunction with traditional antibiotics to prevent and/or cure chronic infections more efficiently than antibiotics alone.

Near-Infrared-Controlled Nanoplatform Exploiting Photothermal Promotion of Peroxidase-like and OXD-like Activities for Potent Antibacterial and Anti-biofilm Therapies

Nanozymes that mimic peroxidase (POD) activity can convert H₂O₂ into bactericidal free radicals, which is referred to as chemodynamic therapy (CDT). High glutathione (GSH) levels in the infectious tissue severely limit the performance of CDT. Herein, we report a near-infrared-controlled antibacterial nanoplatform that is based on encapsulating tungsten sulfide quantum dots (WS₂QDs) and the antibiotic vancomycin in a thermal-sensitive liposome. The system exploits the photothermal sensitivity of the WS₂QDs to achieve selective liposome rupture for the targeted drug delivery. We determined that WS₂QDs show a strong POD-like activity under physiological conditions and the oxidase-like activity, which can oxidate GSH to further improve the CDT efficacy. Moreover, we found that increased temperature promotes multiple enzyme-mimicking activities of WS₂QDs. This platform exerts antibacterial effects against Gram-positive Mu50 (a vancomycin-intermediate Staphylococcus aureus reference strain) and Gram-negative Escherichia coli and disrupts biofilms for improved penetration of therapeutic agents inside biofilms. In vivo studies with mice bearing Mu50-caused skin abscess revealed that this platform confers potent antibacterial activity without obvious toxicity. Accordingly, our work illustrates that the photothermal and nanozyme properties of WS₂QDs can be deployed alongside a conventional therapeutic to achieve synergistic chemodynamic/photothermal/pharmaco therapy for powerful antibacterial effects.

H2S and reactive sulfur signaling at the host-bacterial pathogen interface

Bacterial pathogens that cause invasive disease in the vertebrate host must adapt to host efforts to cripple their viability. Major host insults are reactive oxygen and reactive nitrogen species as well as cellular stress induced by antibiotics. Hydrogen sulfide (H2S) is emerging as an important player in cytoprotection against these stressors, which may well be attributed to downstream more oxidized sulfur species termed reactive sulfur species (RSS). In this review, we summarize recent work that suggests that H2S/RSS impacts bacterial survival in infected cells and animals. We discuss the mechanisms of biogenesis and clearance of RSS in the context of a bacterial H2S/RSS homeostasis model and the bacterial transcriptional regulatory proteins that act as "sensors" of cellular RSS that maintain H2S/RSS homeostasis. In addition, we cover fluorescence imaging- and MS-based approaches used to detect and quantify RSS in bacterial cells. Last, we discuss proteome persulfidation (S-sulfuration) as a potential mediator of H2S/RSS signaling in bacteria in the context of the writer-reader-eraser paradigm, and progress toward ascribing regulatory significance to this widespread post-translational modification.

Fostering Innovation in the Treatment of Chronic Polymicrobial Cystic Fibrosis-Associated Infections Exploring Aspartic Acid and Succinic Acid as Ciprofloxacin Adjuvants

Cystic fibrosis (CF) disease provokes the accumulation of thick and viscous sputum in the lungs, favoring the development of chronic and polymicrobial infections. Pseudomonas aeruginosa is the main bacterium responsible for these chronic infections, and much of the difficulty involved in eradicating it is due to biofilm formation. However, this could be mitigated using adjuvant compounds that help or potentiate the antibiotic action. Therefore, the main goal of this study was to search for substances that function as adjuvants and also as biofilm-controlling compounds, preventing or dismantling P. aeruginosa biofilms formed in an in vitro CF airway environment. Dual combinations of compounds with subinhibitory (1 and 2 mg/L) and inhibitory concentrations (4 mg/L) of ciprofloxacin were tested to inhibit the bacterial growth and biofilm formation (prophylactic approach) and to eradicate 24-h-old P. aeruginosa populations, including planktonic cells and biofilms (treatment approach). Our results revealed that aspartic acid (Asp) and succinic acid (Suc) restored ciprofloxacin action against P. aeruginosa. Suc combined with 2 mg/L of ciprofloxacin (Suc-Cip) was able to eradicate bacteria, and Asp combined with 4 mg/L of ciprofloxacin (Asp–Cip) seemed to eradicate the whole 24-h-old populations, including planktonic cells and biofilms. Based on biomass depletion data, we noted that Asp induced cell death and Suc seemed somehow to block or reduce the expression of ciprofloxacin resistance. As far as we know, this kind of action had not been reported up till now. The presence of Staphylococcus aureus and Burkholderia cenocepacia did not affect the efficacy of the Asp–Cip and Suc–Cip therapies against P. aeruginosa and, also important, P. aeruginosa depletion from polymicrobial communities did not create a window of opportunity for these species to thrive. Rather the contrary, Asp and Suc also improved ciprofloxacin action against B. cenocepacia. Further studies on the cytotoxicity using lung epithelial cells indicated toxicity of Suc–Cip caused by the Suc. In conclusion, we provided evidences that Asp and Suc could be potential ciprofloxacin adjuvants to eradicate P. aeruginosa living within polymicrobial communities. Asp–Cip and Suc–Cip could be promising therapeutic options to cope with CF treatment failures.

Surface Charge Switchable Supramolecular Nanocarriers for Nitric Oxide Synergistic Photodynamic Eradication of Biofilms

Biofilm has resulted in numerous obstinate clinical infections, posing severe threats to public health. It is urgent to develop original antibacterial strategies for eradicating biofilms. Herein, we develop a surface charge switchable supramolecular nanocarrier exhibiting pH-responsive penetration into an acidic biofilm for nitric oxide (NO) synergistic photodynamic eradication of the methicillin-resistant Staphylococcus aureus (MRSA) biofilm with negligible damage to healthy tissues under laser irradiation. Originally, by integrating the glutathione (GSH)-sensitive α-cyclodextrin (α-CD) conjugated nitric oxide (NO) prodrug (α-CD-NO) and chlorin e6 (Ce6) prodrug (α-CD-Ce6) into the pH-sensitive poly(ethylene glycol) (PEG) block polypeptide copolymer (PEG-(KLAKLAK)2-DA) via host-guest interaction, the supramolecular nanocarrier α-CD-Ce6-NO-DA was finely prepared. The supramolecular nanocarrier shows complete surface charge reversal from negative charge at physiological pH (7.4) to positive charge at acidic biofilm pH (5.5), promoting efficient penetration into the biofilm. Once infiltrated into the biofilm, the nanocarrier exhibits rapid NO release triggered by the overexpressed GSH in the biofilm, which not only produces abundant NO for killing bacteria but also reduces the biofilm GSH level to improve photodynamic therapy (PDT) efficiency. On the other hand, NO can react with reactive oxygen species (ROS) to produce reactive nitrogen species (RNS), further improving the PDT efficiency. Due to the effective penetration into the biofilm and depletion of biofilm GSH, the surface charge switchable GSH-sensitive NO nanocarrier can greatly improve the PDT efficiency at a low photosensitizer dose and laser intensity and cause negligible side effect to healthy tissues. Considering the above advantages, the strategy developed in this work may offer great possibilities to fight against biofilm infections.

Conditions Under Which Glutathione Disrupts the Biofilms and Improves Antibiotic Efficacy of Both ESKAPE and Non-ESKAPE Species

Bacterial antibiotic resistance has increased in recent decades, raising concerns in hospital and community settings. Novel, innovative strategies are needed to eradicate bacteria, particularly within biofilms, and diminish the likelihood of recurrence. In this study, we investigated whether glutathione (GSH) can act as a biofilm disruptor, and enhance antibiotic effectiveness against various bacterial pathogens. Biological levels (10 mM) of GSH did not have a significant effect in inhibiting growth or disrupting the biofilm in four out of six species tested. However, exposure to 30 mM GSH showed >50% decrease in growth for all bacterial species, with almost 100% inhibition of Streptococcus pyogenes and an average of 94-52% inhibition for Escherichia coli, Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive S. aureus (MSSA) and multi-drug resistant Acinetobacter baumannii (MRAB) isolates, respectively. Klebsiella pneumoniae and Enterobacter sp. isolates were however, highly resistant to 30 mM GSH. With respect to biofilm viability, all species exhibited a >50% decrease in viability with 30 mM GSH, with confocal imaging showing considerable change in the biofilm architecture of MRAB isolates. The mechanism of GSH-mediated biofilm disruption is possibly due to a concentration-dependent increase in GSH acidity that triggers cleaving of the matrix components. Enzymatic treatment of MRAB revealed that eDNA and polysaccharides are essential for biofilm stability and eDNA removal enhanced amikacin efficiency. Combination of GSH, amikacin and DNase-I showed the greatest reduction in MRAB biofilm viability. Additionally, GSH alone and in combination with amikacin fostered human fibroblast cell (HFF-1) growth and confluence while inhibiting MRAB adhesion and colonization.

Can Biofilm Be Reversed Through Quorum Sensing in Pseudomonas aeruginosa?

Pseudomonas aeruginosa is a Gram-negative bacterium causing diseases in plants, animals, and humans, and its drug resistance is a major concern in medical care. Biofilms play an important role in P. aeruginosa drug resistance. Three factors are most important to induce biofilm: quorum sensing (QS), bis-(3′-5′)-cyclic diguanosine monophosphate (c-di-GMP), and small RNAs (sRNAs). P. aeruginosa has its own specific QS system (PQS) besides two common QS systems, LasI–LasR and RhlI–RhlR, in bacteria. PQS is interesting not only because there is a negative regulation from RhlR to pqsR but also because the null mutation in PQS leads to a reduced biofilm formation. Furthermore, P. aeruginosa dispersed cells have physiological features that are distinct between the planktonic cells and biofilm cells. In response to a low concentration of c-di-GMP, P. aeruginosa cells can disperse from the biofilms to become planktonic cells. These raise an interesting hypothesis of whether biofilm can be reversed through the QS mechanism in P. aeruginosa. Although a single factor is certainly not sufficient to prevent the biofilm formation, it necessarily explores such possibility. In this hypothesis, the literature is analyzed to determine the negative regulation pathways, and then the transcriptomic data are analyzed to determine whether this hypothesis is workable or not. Unexpectedly, the transcriptomic data reveal a negative regulation between lasI and psqR. Also, the individual cases from transcriptomic data demonstrate the negative regulations of PQS with laslI, laslR, rhlI, and rhlR under different experiments. Based on our analyses, possible strategies to reverse biofilm formation are proposed and their clinic implications are addressed.

Global Transcriptome Changes of Biofilm-Forming Staphylococcus epidermidis Responding to Total Alkaloids of Sophorea alopecuroides

Transcriptome changes of biofilm-forming Staphylococcus epidermidis response to total alkaloids of Sophorea alopecuroides was observed. Bioinformatic analyses were further used to compare the differential gene expression between control and the treated samples. It was found that 282 genes were differentially expressed, with 92 up-regulated and 190 down-regulated. These involved down-regulation of the sulfur metabolism pathway. It was suggested that inhibitory effects on Staphylococcus epidermidis and its biofilm formation of the total alkaloids of S. alopecuroides was mainly due to the regulation of the sulfur metabolism pathways of S. epidermidis.

Spray-Dried Particles of Nitric Oxide-Modified Glutathione for the Treatment of Chronic Lung Infection

Antibiotic resistance in pathogenic bacteria has emerged as a big challenge to human and animal health and significant economy loss worldwide. Development of novel strategies to tackle antibiotic resistance is of the utmost priority. In this study, we combined glutathione (GSH), a master antioxidant in all mammalian cells, and nitric oxide, a proven biofilm-dispersing agent, to produce GSNO. The resazurin biofilm viability assay, crystal violet biofilm assay, and confocal microscopy techniques showed that GSNO disrupted biofilms of both P. aeruginosa PAO1 and multidrug resistant A. baumaunii (MRAB 015069) more efficiently than GSH alone. In addition, GSNO showed a higher reduction in biofilm viability and biomass when combined with antibiotics. This combination treatment also inhibited A. baumaunii (MRAB 015069) growth and facilitated human foreskin fibroblast (HFF-1) confluence and growth simultaneously. A potentially inhalable GSNO powder with reasonable aerosol performance and antibiofilm activity was produced by spray drying. This combination shows promise as a novel formulation for treating pulmonary bacterial infections.

Current anti-biofilm strategies and potential of antioxidants in biofilm control

INTRODUCTION

Biofilm formation is a strategy for microorganisms to adapt and survive in hostile environments. Microorganisms that are able to produce biofilms are currently recognized as a threat to human health. Areas covered: Many strategies have been employed to eradicate biofilms, but several drawbacks from these methods had subsequently raised concerns on the need for alternative approaches to effectively prevent biofilm formation. One of the main mechanisms that drives a microorganism to transit from a planktonic to a biofilm-sessile state, is oxidative stress. Chemical agents that could target oxidative stress regulators, for instance antioxidants, could therefore be used to treat biofilm-associated infections. Expert commentary: The focus of this review is to summarize the function and limitation of the current anti-biofilm strategies and will propose the use of antioxidants as an alternative method to treat, prevent and eradicate biofilms. Studies have shown that water-soluble and lipid-soluble antioxidants can reduce and prevent biofilm formation, by influencing the expression of genes associated with oxidative stress. Further in vivo work should be conducted to ensure the efficacy of these antioxidants in a biological environment. Nevertheless, antioxidants are promising anti-biofilm agents, and thus is a potential solution for biofilm-associated infections in the future.

Pseudomonas aeruginosa glutathione biosynthesis genes play multiple roles in stress protection, bacterial virulence and biofilm formation

Pseudomonas aeruginosa PAO1 contains gshA and gshB genes, which encode enzymes involved in glutathione (GSH) biosynthesis. Challenging P. aeruginosa with hydrogen peroxide, cumene hydroperoxide, and t-butyl hydroperoxide increased the expression of gshA and gshB. The physiological roles of these genes in P. aeruginosa oxidative stress, bacterial virulence, and biofilm formation were examined using P. aeruginosa ΔgshA, ΔgshB, and double ΔgshAΔgshB mutant strains. These mutants exhibited significantly increased susceptibility to methyl viologen, thiol-depleting agent, and methylglyoxal compared to PAO1. Expression of functional gshA, gshB or exogenous supplementation with GSH complemented these phenotypes, which indicates that the observed mutant phenotypes arose from their inability to produce GSH. Virulence assays using a Drosophila melanogaster model revealed that the ΔgshA, ΔgshB and double ΔgshAΔgshB mutants exhibited attenuated virulence phenotypes. An analysis of virulence factors, including pyocyanin, pyoverdine, and cell motility (swimming and twitching), showed that these levels were reduced in these gsh mutants compared to PAO1. In contrast, biofilm formation increased in mutants. These data indicate that the GSH product and the genes responsible for GSH synthesis play multiple crucial roles in oxidative stress protection, bacterial virulence and biofilm formation in P. aeruginosa.

Antibiofilm Effect of DNase against Single and Mixed Species Biofilm

Biofilms are aggregates of microorganisms that coexist in socially coordinated micro-niche in a self-produced polymeric matrix on pre-conditioned surfaces. The biofilm matrix reduces the efficacy of antibiofilm strategies. DNase degrades the extracellular DNA (e-DNA) present in the matrix, rendering the matrix weak and susceptible to antimicrobials. In the current study, the effect of DNase I was evaluated during biofilm formation (pre-treatment), on preformed biofilms (post-treatment) and both (dual treatment). The DNase I pre-treatment was optimized for P. aeruginosa PAO1 (model biofilm organism) at 10 µg/mL and post-treatment at 10 µg/mL with 15 min of contact duration. Inclusion of Mg2+ alongside DNase I post-treatment resulted in 90% reduction in biofilm within only 5 min of contact time (irrespective of age of biofilm). On extension of these findings, DNase I was found to be less effective against mixed species biofilm than individual biofilms. DNase I can be used as potent antibiofilm agent and with further optimization can be effectively used for biofilm prevention and reduction in situ.

Eradication of P. aeruginosa biofilm in endotracheal tubes based on lock therapy: results from an in vitro study

Background

Despite the several strategies available for the management of biofilm-associated ventilator-associated pneumonia, data regarding the efficacy of applying antibiotics to the subglottic space (SS) are scarce. We created an in vitro model to assess the efficacy of antibiotic lock therapy (ALT) applied in the SS for eradication of Pseudomonas aeruginosa biofilm in endotracheal tubes (ETTs).

Methods

We applied 2 h of ALT to a P. aeruginosa biofilm in ETTs using a single dose (SD) and a 5-day therapy model (5D). We used sterile saline lock therapy (SLT) as the positive control. We compared colony count and the percentage of live cells between both models.

Results

The median (IQR) cfu counts/ml and percentage of live cells in the SD-ALT and SD-SLT groups were, respectively, 3.12 × 10⁵ (9.7 × 10⁴-0) vs. 8.16 × 10⁷ (7.0 × 10⁷-0) (p = 0.05) and 53.2% (50.9%-57.2%) vs. 91.5% (87.3%-93.9%) (p < 0.001). The median (IQR) cfu counts/ml and percentage of live cells in the 5D-ALT and 5D-SLT groups were, respectively, 0 (0-0) vs. 3.2 × 10⁷ (2.32 × 10⁷-0) (p = 0.03) and 40.6% (36.6%-60.0%) vs. 90.3% (84.8%-93.9%) (p < 0.001).

Conclusion

We demonstrated a statistically significant decrease in the viability of P. aeruginosa biofilm after application of 5D-ALT in the SS. Future clinical studies to assess ALT in patients under mechanical ventilation are needed.