Neutrophil enhancement of Pseudomonas aeruginosa biofilm development: human F-actin and DNA as targets for therapy

Ceragenin-mediated disruption of Pseudomonas aeruginosa biofilms

BACKGROUND

Microbial biofilms, as a hallmark of cystic fibrosis (CF) lung disease and other chronic infections, remain a desirable target for antimicrobial therapy. These biopolymer-based viscoelastic structures protect pathogenic organisms from immune responses and antibiotics. Consequently, treatments directed at disrupting biofilms represent a promising strategy for combating biofilm-associated infections. In CF patients, the viscoelasticity of biofilms is determined mainly by their polymicrobial nature and species-specific traits, such as Pseudomonas aeruginosa filamentous (Pf) bacteriophages. Therefore, we examined the impact of microbicidal ceragenins (CSAs) supported by mucolytic agents-DNase I and poly-aspartic acid (pASP), on the viability and viscoelasticity of mono- and bispecies biofilms formed by Pf-positive and Pf-negative P. aeruginosa strains co-cultured with Staphylococcus aureus or Candida albicans.

METHODS

The in vitro antimicrobial activity of ceragenins against P. aeruginosa in mono- and dual-species cultures was assessed by determining minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC). Inhibition of P. aeruginosa mono- and dual-species biofilms formation by ceragenins alone and in combination with DNase I or poly-aspartic acid (pASP) was estimated by the crystal violet assay. Additionally, the viability of the biofilms was measured by colony-forming unit (CFU) counting. Finally, the biofilms' viscoelastic properties characterized by shear storage (G') and loss moduli (G"), were analyzed with a rotational rheometer.

RESULTS

Our results demonstrated that ceragenin CSA-13 inhibits biofilm formation and increases its fluidity regardless of the Pf-profile and species composition; however, the Pf-positive biofilms are characterized by elevated viscosity and elasticity parameters.

CONCLUSION

Due to its microbicidal and viscoelasticity-modifying properties, CSA-13 displays therapeutic potential in biofilm-associated infections, especially when combined with mucolytic agents.

Safety, tolerability, and effect of a single aural dose of Dornase alfa at the time of ventilation tube surgery for otitis media: A Phase 1b double randomized control trial

BACKGROUND

One third of children require repeat ventilation tube insertion (VTI) for otitis media. Disease recurrence is associated with persistent middle ear bacterial biofilms. With demonstration that Dornase alfa (a DNase) disrupts middle ear effusion biofilms ex vivo, we identified potential for this as an anti-biofilm therapy to prevent repeat VTI. First, safety and tolerability needed to be measured.

METHODS

This was a phase 1B double-blinded randomized control trial conducted in Western Australia. Children between 6 months and 5 years undergoing VTI for bilateral middle ear effusion were recruited between 2012 and 2014 and followed for two years. Children's ears were randomized to receive either Dornase alfa (1 mg/mL) or 0.9 % sodium chloride (placebo) at time of surgery. Children were followed up at 2 weeks post-VTI and at 3-monthly intervals for 2 years. Outcomes assessed were: 1) safety and tolerability, 2) otorrhoea frequency, 3) blocked or extruded ventilation tube (VT) frequency, 4) time to blockage or extrusion, 5) time to infection recurrence and/or need for repeat VTI.

RESULTS

Sixty children (mean age 2.3 years) were enrolled with 87 % reaching study endpoint. Treatment did not change otorrhoea frequency. Hearing improved in all children following VTI, with no indication of ototoxicity. Dornase alfa had some effect on increasing time until VT extrusion (p = 0.099); and blockage and/or extrusion (p = 0.122). Frequency of recurrence and time until recurrence were similar. Fourteen children required repeat VTI within the follow-up period.

CONCLUSION

A single application of Dornase alfa into the middle ear at time of VTI was safe, non-ototoxic, and well-tolerated.

TRIAL REGISTRATION

ACTRN12623000504617.

Natural and synthetic molecules with potential to enhance biofilm formation and virulence properties in Pseudomonas aeruginosa

Pseudomonas aeruginosa can efficiently adapt to changing environmental conditions due to its ubiquitous nature, intrinsic/acquired/adaptive resistance mechanisms, high metabolic versatility, and the production of numerous virulence factors. As a result, P. aeruginosa becomes an opportunistic pathogen, causing chronic infection in the lungs and several organs of patients suffering from cystic fibrosis. Biofilm established by P. aeruginosa in host tissues and medical device surfaces has been identified as a major obstruction to antimicrobial therapy. P. aeruginosa is very likely to be closely associated with the various microorganisms in the host tissues or organs in a pathogenic or nonpathogenic behavior. Aside from host-derived molecules, other beneficial and pathogenic microorganisms produce a diverse range of secondary metabolites that either directly or indirectly favor the persistence of P. aeruginosa. Thus, it is critical to understand how P. aeruginosa interacts with different molecules and ions in the host and abiotic environment to produce extracellular polymeric substances and virulence factors. Thus, the current review discusses how various natural and synthetic molecules in the environment induce biofilm formation and the production of multiple virulence factors.

Nanotechnology-Based Drug Delivery Systems to Control Bacterial-Biofilm-Associated Lung Infections

Airway mucus dysfunction and impaired immunological defenses are hallmarks of several lung diseases, including asthma, cystic fibrosis, and chronic obstructive pulmonary diseases, and are mostly causative factors in bacterial-biofilm-associated respiratory tract infections. Bacteria residing within the biofilm architecture pose a complex challenge in clinical settings due to their increased tolerance to currently available antibiotics and host immune responses, resulting in chronic infections with high recalcitrance and high rates of morbidity and mortality. To address these unmet clinical needs, potential anti-biofilm therapeutic strategies are being developed to effectively control bacterial biofilm. This review focuses on recent advances in the development and application of nanoparticulate drug delivery systems for the treatment of biofilm-associated respiratory tract infections, especially addressing the respiratory barriers of concern for biofilm accessibility and the various types of nanoparticles used to combat biofilms. Understanding the obstacles facing pulmonary drug delivery to bacterial biofilms and nanoparticle-based approaches to combatting biofilm may encourage researchers to explore promising treatment modalities for bacterial-biofilm-associated chronic lung infections.

Low Concentration of the Neutrophil Proteases Cathepsin G, Cathepsin B, Proteinase-3 and Metalloproteinase-9 Induce Biofilm Formation in Non-Biofilm-Forming Staphylococcus epidermidis Isolates

Neutrophils play a crucial role in eliminating bacteria that invade the human body; however, cathepsin G can induce biofilm formation in a non-biofilm-forming Staphylococcus epidermidis 1457 strain, suggesting that neutrophil proteases may be involved in biofilm formation. Cathepsin G, cathepsin B, proteinase-3, and metalloproteinase-9 (MMP-9) from neutrophils were tested on the biofilm induction in commensal (skin isolated) and clinical non-biofilm-forming S. epidermidis isolates. From 81 isolates, 53 (74%) were aap+, icaA−, icaD− genotype, and without the capacity of biofilm formation under conditions of 1% glucose, 4% ethanol or 4% NaCl, but these 53 non-biofilm-forming isolates induced biofilm by the use of different neutrophil proteases. Of these, 62.3% induced biofilm with proteinase-3, 15% with cathepsin G, 10% with cathepsin B and 5% with MMP -9, where most of the protease-induced biofilm isolates were commensal strains (skin). In the biofilm formation kinetics analysis, the addition of phenylmethylsulfonyl fluoride (PMSF; a proteinase-3 inhibitor) showed that proteinase-3 participates in the cell aggregation stage of biofilm formation. A biofilm induced with proteinase-3 and DNAse-treated significantly reduced biofilm formation at an early time (initial adhesion stage of biofilm formation) compared to untreated proteinase-3-induced biofilm (p < 0.05). A catheter inoculated with a commensal (skin) non-biofilm-forming S. epidermidis isolate treated with proteinase-3 and another one without the enzyme were inserted into the back of a mouse. After 7 days of incubation period, the catheters were recovered and the number of grown bacteria was quantified, finding a higher amount of adhered proteinase-3-treated bacteria in the catheter than non-proteinase-3-treated bacteria (p < 0.05). Commensal non-biofilm-forming S. epidermidis in the presence of neutrophil cells significantly induced the biofilm formation when multiplicity of infection (MOI) 1:0.01 (neutrophil:bacteria) was used, but the addition of a cocktail of protease inhibitors impeded biofilm formation. A neutrophil:bacteria assay did not induce neutrophil extracellular traps (NETs). Our results suggest that neutrophils, in the presence of commensal non-biofilm-forming S. epidermidis, do not generate NETs formation. The effect of neutrophils is the production of proteases, and proteinase-3 releases bacterial DNA at the initial adhesion, favoring cell aggregation and subsequently leading to biofilm formation.

Immunometabolism in biofilm infection: lessons from cancer

BACKGROUND

Biofilm is a community of bacteria embedded in an extracellular matrix, which can colonize different human cells and tissues and subvert the host immune reactions by preventing immune detection and polarizing the immune reactions towards an anti-inflammatory state, promoting the persistence of biofilm-embedded bacteria in the host.

MAIN BODY OF THE MANUSCRIPT

It is now well established that the function of immune cells is ultimately mediated by cellular metabolism. The immune cells are stimulated to regulate their immune functions upon sensing danger signals. Recent studies have determined that immune cells often display distinct metabolic alterations that impair their immune responses when triggered. Such metabolic reprogramming and its physiological implications are well established in cancer situations. In bacterial infections, immuno-metabolic evaluations have primarily focused on macrophages and neutrophils in the planktonic growth mode.

CONCLUSION

Based on differences in inflammatory reactions of macrophages and neutrophils in planktonic- versus biofilm-associated bacterial infections, studies must also consider the metabolic functions of immune cells against biofilm infections. The profound characterization of the metabolic and immune cell reactions could offer exciting novel targets for antibiofilm therapy.

Pseudomonas aeruginosa Biofilm Formation and Its Control

Microbes are hardly seen as planktonic species and are most commonly found as biofilm communities in cases of chronic infections. Biofilms are regarded as a biological condition, where a large group of microorganisms gets adhered to a biotic or abiotic surface. In this context, Pseudomonas aeruginosa, a Gram-negative nosocomial pathogen is the main causative organism responsible for life-threatening and persistent infections in individuals affected with cystic fibrosis and other lung ailments. The bacteria can form a strong biofilm structure when it adheres to a surface suitable for the development of a biofilm matrix. These bacterial biofilms pose higher natural resistance to conventional antibiotic therapy due to their multiple tolerance mechanisms. This prevailing condition has led to an increasing rate of treatment failures associated with P. aeruginosa biofilm infections. A better understanding of the effect of a diverse group of antibiotics on established biofilms would be necessary to avoid inappropriate treatment strategies. Hence, the search for other alternative strategies as effective biofilm treatment options has become a growing area of research. The current review aims to give an overview of the mechanisms governing biofilm formation and the different strategies employed so far in the control of biofilm infections caused by P. aeruginosa. Moreover, this review can also help researchers to search for new antibiofilm agents to tackle the effect of biofilm infections that are currently imprudent to conventional antibiotics.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Treatment with a neutrophil elastase inhibitor and ofloxacin reduces P. aeruginosa burden in a mouse model of chronic suppurative otitis media

Chronic suppurative otitis media (CSOM) is a widespread, debilitating problem with poorly understood immunology. Here, we assess the host response to middle ear infection over the course of a month post-infection in a mouse model of CSOM and in human subjects with the disease. Using multiparameter flow cytometry and a binomial generalized linear machine learning model, we identified Ly6G, a surface marker of mature neutrophils, as the most informative factor of host response driving disease in the CSOM mouse model. Consistent with this, neutrophils were the most abundant cell type in infected mice and Ly6G expression tracked with the course of infection. Moreover, neutrophil-specific immunomodulatory treatment using the neutrophil elastase inhibitor GW 311616A significantly reduces bacterial burden relative to ofloxacin-only treated animals in this model. The levels of dsDNA in middle ear effusion samples are elevated in both humans and mice with CSOM and decreased during treatment, suggesting that dsDNA may serve as a molecular biomarker of treatment response. Together these data strongly implicate neutrophils in the ineffective immune response to P. aeruginosa infection in CSOM and suggest that immunomodulatory strategies may benefit drug-tolerant infections for chronic biofilm-mediated disease.

Immune Responses to Pseudomonas aeruginosa Biofilm Infections

Pseudomonas aeruginosa is a key pathogen of chronic infections in the lungs of cystic fibrosis patients and in patients suffering from chronic wounds of diverse etiology. In these infections the bacteria congregate in biofilms and cannot be eradicated by standard antibiotic treatment or host immune responses. The persistent biofilms induce a hyper inflammatory state that results in collateral damage of the adjacent host tissue. The host fails to eradicate the biofilm infection, resulting in hindered remodeling and healing. In the present review we describe our current understanding of innate and adaptive immune responses elicited by P. aeruginosa biofilms in cystic fibrosis lung infections and chronic wounds. This includes the mechanisms that are involved in the activation of the immune responses, as well as the effector functions, the antimicrobial components and the associated tissue destruction. The mechanisms by which the biofilms evade immune responses, and potential treatment targets of the immune response are also discussed.

Effect of Polyhexamethylene Biguanide in Combination with Undecylenamidopropyl Betaine or PslG on Biofilm Clearance

Hospital-acquired infection is a great challenge for clinical treatment due to pathogens’ biofilm formation and their antibiotic resistance. Here, we investigate the effect of antiseptic agent polyhexamethylene biguanide (PHMB) and undecylenamidopropyl betaine (UB) against biofilms of four pathogens that are often found in hospitals, including Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, Gram-positive bacteria Staphylococcus aureus, and pathogenic fungus, Candida albicans. We show that 0.02% PHMB, which is 10-fold lower than the concentration of commercial products, has a strong inhibitory effect on the growth, initial attachment, and biofilm formation of all tested pathogens. PHMB can also disrupt the preformed biofilms of these pathogens. In contrast, 0.1% UB exhibits a mild inhibitory effect on biofilm formation of the four pathogens. This concentration inhibits the growth of S. aureus and C. albicans yet has no growth effect on P. aeruginosa or E. coli. UB only slightly enhances the anti-biofilm efficacy of PHMB on P. aeruginosa biofilms. However, pretreatment with PslG, a glycosyl hydrolase that can efficiently inhibit and disrupt P. aeruginosa biofilm, highly enhances the clearance effect of PHMB on P. aeruginosa biofilms. Meanwhile, PslG can also disassemble the preformed biofilms of the other three pathogens within 30 min to a similar extent as UB treatment for 24 h.

Biofilms as Promoters of Bacterial Antibiotic Resistance and Tolerance

Multidrug resistant bacteria are a global threat for human and animal health. However, they are only part of the problem of antibiotic failure. Another bacterial strategy that contributes to their capacity to withstand antimicrobials is the formation of biofilms. Biofilms are associations of microorganisms embedded a self-produced extracellular matrix. They create particular environments that confer bacterial tolerance and resistance to antibiotics by different mechanisms that depend upon factors such as biofilm composition, architecture, the stage of biofilm development, and growth conditions. The biofilm structure hinders the penetration of antibiotics and may prevent the accumulation of bactericidal concentrations throughout the entire biofilm. In addition, gradients of dispersion of nutrients and oxygen within the biofilm generate different metabolic states of individual cells and favor the development of antibiotic tolerance and bacterial persistence. Furthermore, antimicrobial resistance may develop within biofilms through a variety of mechanisms. The expression of efflux pumps may be induced in various parts of the biofilm and the mutation frequency is induced, while the presence of extracellular DNA and the close contact between cells favor horizontal gene transfer. A deep understanding of the mechanisms by which biofilms cause tolerance/resistance to antibiotics helps to develop novel strategies to fight these infections.

Corneal Infection Models: Tools to Investigate the Role of Biofilms in Bacterial Keratitis

Bacterial keratitis is a corneal infection which may cause visual impairment or even loss of the infected eye. It remains a major cause of blindness in the developing world. Staphylococcus aureus and Pseudomonas aeruginosa are common causative agents and these bacterial species are known to colonise the corneal surface as biofilm populations. Biofilms are complex bacterial communities encased in an extracellular polymeric matrix and are notoriously difficult to eradicate once established. Biofilm bacteria exhibit different phenotypic characteristics from their planktonic counterparts, including an increased resistance to antibiotics and the host immune response. Therefore, understanding the role of biofilms will be essential in the development of new ophthalmic antimicrobials. A brief overview of biofilm-specific resistance mechanisms is provided, but this is a highly multifactorial and rapidly expanding field that warrants further research. Progression in this field is dependent on the development of suitable biofilm models that acknowledge the complexity of the ocular environment. Abiotic models of biofilm formation (where biofilms are studied on non-living surfaces) currently dominate the literature, but co-culture infection models are beginning to emerge. In vitro, ex vivo and in vivo corneal infection models have now been reported which use a variety of different experimental techniques and animal models. In this review, we will discuss existing corneal infection models and their application in the study of biofilms and host-pathogen interactions at the corneal surface.

Innate and Adaptive Immune Responses against Bordetella pertussis and Pseudomonas aeruginosa in a Murine Model of Mucosal Vaccination against Respiratory Infection

Whole cell vaccines are frequently the first generation of vaccines tested for pathogens and can inform the design of subsequent acellular or subunit vaccines. For respiratory pathogens, administration of vaccines at the mucosal surface can facilitate the generation of a localized mucosal immune response. Here, we examined the innate and vaccine-induced immune responses to infection by two respiratory pathogens: Bordetella pertussis and Pseudomonas aeruginosa. In a model of intranasal administration of whole cell vaccines (WCVs) with the adjuvant curdlan, we examined local and systemic immune responses following infection. These studies showed that intranasal vaccination with a WCV led to a reduction of the bacterial burden in the airways of animals infected with the respective pathogen. However, there were unique changes in the cytokines produced, cells recruited, and inflammation at the site of infection. Both mucosal vaccinations induced antibodies that bind the target pathogen, but linear regression and principal component analysis revealed that protection from these pathogens is not solely related to antibody titer. Protection from P. aeruginosa correlated to a reduction in lung weight, blood lymphocytes and neutrophils, and the cytokines IL-6, TNF-α, KC/GRO, and IL-10, and promotion of serum IgG antibodies and the cytokine IFN-γ in the lung. Protection from B. pertussis infection correlated strongly with increased anti-B-pertussis serum IgG antibodies. These findings reveal valuable correlates of protection for mucosal vaccination that can be used for further development of both B. pertussis and P. aeruginosa vaccines.

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.

Specific Disruption of Established Pseudomonas aeruginosa Biofilms Using Polymer-Attacking Enzymes

Biofilms are communities of bacteria embedded in a polymeric matrix which are found in infections and in environments outside the body. Breaking down the matrix renders biofilms more susceptible to physical disruption and to treatments such as antibiotics. Different species of bacteria, and different strains within the same species, produce different types of matrix polymers. This suggests that targeting specific polymers for disruption may be more effective than nonspecific approaches to disrupting biofilm matrixes. In this study, we treated Pseudomonas aeruginosa biofilms with enzymes that are specific to different matrix polymers. We measured the resulting alteration in biofilm mechanics using bulk rheology and changes in structure using electron microscopy. We find that, for biofilms grown in vitro, the effect of enzymatic treatment is greatest when the enzyme is specific to a dominant matrix polymer. Specifically matched enzymatic treatment tends to reduce yield strain and yield stress and increase the rate of biofilm drying, due to increased diffusivity as a result of network compromise. Electron micrographs qualitatively suggest that well-matched enzymatic treatments reduce long-range structure and shorten connecting network fibers. Previous work has shown that generic glycoside hydrolases can cause dispersal of bacteria from in vivo and ex vivo biofilms into a free-swimming state, and thereby make antibiotic treatment more effective. For biofilms grown in wounded mice, we find that well-matched treatments that result in the greatest mechanical compromise in vitro induce the least dispersal ex vivo. Moreover, we find that generic glycoside hydrolases have no measurable effect on the mechanics of biofilms grown in vitro, while previous work has shown them to be highly effective at inducing dispersal in vivo and ex vivo. This highlights the possibility that effective approaches to eradicating biofilms may depend strongly on the growth environment.

Detrimental Effect of Type I IFNs During Acute Lung Infection With Pseudomonas aeruginosa Is Mediated Through the Stimulation of Neutrophil NETosis

Pseudomonas aeruginosa is an opportunistic multidrug-resistant pathogen, able to grow in biofilms. It causes life-threatening complications in diseases characterized by the up-regulation of type I interferon (IFN) signaling, such as cancer or viral infections. Since type I IFNs regulate multiple functions of neutrophils, which constitute the first line of anti-bacterial host defense, in this work we aimed to study how interferon-activated neutrophils influence the course of P. aeruginosa infection of the lung. In lungs of infected IFN-sufficient WT mice, significantly elevated bacteria load was observed, accompanied by the prominent lung tissue damage. At the same time IFN-deficient animals seem to be partly resistant to the infection. Lung neutrophils from such IFN-deficient animals release significantly lower amounts of neutrophil extracellular traps (NETs) and reactive oxygen species (ROS), as compared to WT neutrophils. Of note, such IFN-deficient neutrophils show significantly decreased capacity to stimulate biofilm formation by P. aeruginosa. Reduced biofilm production impairs in turn the survival of bacteria in a lung tissue. In line with that, treatment of neutrophils with recombinant IFN-β enhances their NETosis and stimulates biofilm formation by Pseudomonas after co-incubation with such neutrophils. Possibly, bacteria utilizes neutrophil-derived NETs as a scaffold for released biofilms. In agreement with this, in vivo treatment with ROS-scavengers, NETs disruption or usage of the bacterial strains unable to bind DNA, suppress neutrophil-mediated biofilm formation in the lungs. Together, our findings indicate that the excessive activation of neutrophils by type I IFNs leads to their boosted NETosis that in turn triggers biofilm formation by P. aeruginosa and supports its persistence in the infected lung. Targeting these mechanisms could offer a new therapeutic approach to prevent persistent bacterial infections in patients with diseases associated with the up-regulation of type I IFNs.

The blood compatibility challenge. Part 3: Material associated activation of blood cascades and cells

Following protein adsorption/activation which is the first step after the contact of material surfaces and whole blood (part 2), fibrinogen is converted to fibrin and platelets become activated and assembled in the form of a thrombus. This thrombus formation is the key feature that needs to be minimized in the creation of materials with low thrombogenicity. Further aspects of blood compatibility that are important on their own are complement and leukocyte activation which are also important drivers of thrombus formation. Hence this review summarizes the state of knowledge on all of these cascades and cells and their interactions. For each cascade or cell type, the chapter distinguishes statements which are in widespread agreement from statements where there is less of a consensus. STATEMENT OF SIGNIFICANCE: This paper is part 3 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

2018 international consensus meeting on musculoskeletal infection: Summary from the biofilm workgroup and consensus on biofilm related musculoskeletal infections

Biofilm-associated implant-related bone and joint infections are clinically important due to the extensive morbidity, cost of care and socioeconomic burden that they cause. Research in the field of biofilms has expanded in the past two decades, however, there is still an immense knowledge gap related to many clinical challenges of these biofilm-associated infections. This subject was assigned to the Biofilm Workgroup during the second International Consensus Meeting on Musculoskeletal Infection held in Philadelphia USA (ICM 2018) (https://icmphilly.com). The main objective of the Biofilm Workgroup was to prepare a consensus document based on a review of the literature, prepared responses, discussion, and vote on thirteen biofilm related questions. The Workgroup commenced discussing and refining responses prepared before the meeting on day one using Delphi methodology, followed by a tally of responses using an anonymized voting system on the second day of ICM 2018. The Working group derived consensus on information about biofilms deemed relevant to clinical practice, pertaining to: (1) surface modifications to prevent/inhibit biofilm formation; (2) therapies to prevent and treat biofilm infections; (3) polymicrobial biofilms; (4) diagnostics to detect active and dormant biofilm in patients; (5) methods to establish minimal biofilm eradication concentration for biofilm bacteria; and (6) novel anti-infectives that are effective against biofilm bacteria. It was also noted that biomedical research funding agencies and the pharmaceutical industry should recognize these areas as priorities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Sputum Active Polymyxin Lipopeptides: Activity against Cystic Fibrosis Pseudomonas aeruginosa Isolates and Their Interactions with Sputum Biomolecules

The mucoid biofilm mode of growth of Pseudomonas aeruginosa (P. aeruginosa) in the lungs of cystic fibrosis patients makes eradication of infections with antibiotic therapy very difficult. The lipopeptide antibiotics polymyxin B and colistin are currently the last-resort therapies for infections caused by multidrug-resistant P. aeruginosa. In the present study, we investigated the antibacterial activity of a series of polymyxin lipopeptides (polymyxin B, colistin, FADDI-003, octapeptin A₃, and polymyxin A₂) against a panel of polymyxin-susceptible and polymyxin-resistant P. aeruginosa cystic fibrosis isolates grown under planktonic or biofilm conditions in artificial sputum and their interactions with sputum component biomolecules. In sputum media under planktonic conditions, the lipopeptides FADDI-003 and octapeptin A₃ displayed very promising activity against the polymyxin-resistant isolate FADDI-PA066 (polymyxin B minimum inhibitory concentration (MIC) = 32 mg/L), while retaining their activity against the polymyxin-sensitive strains FADDI-PA021 (polymyxin B MIC = 1 mg/L) and FADDI-PA020 (polymyxin B MIC = 2 mg/L). Polymyxin A₂ was only effective against the polymyxin-sensitive isolates. However, under biofilm growth conditions, the hydrophobic lipopeptide FADDI-003 was inactive compared to the more hydrophilic lipopeptides, octapeptin A₃, polymyxin A₂, polymyxin B, and colistin. Transmission electron micrographs revealed octapeptin A₃ caused reduction in the cell numbers in biofilm as well as biofilm disruption/“antibiofilm” activity. We therefore assessed the interactions of the lipopeptides with the component sputum biomolecules, mucin, deoxyribonucleic acid (DNA), surfactant, F-actin, lipopolysaccharide, and phospholipids. We observed the general trend that sputum biomolecules reduce lipopeptide antibacterial activity. Collectively, our data suggests that, in the airways, lipopeptide binding to component sputum biomolecules may reduce antibacterial efficacy and is dependent on the physicochemical properties of the lipopeptide.

Challenges and Promises for Planning Future Clinical Research Into Bacteriophage Therapy Against Pseudomonas aeruginosa in Cystic Fibrosis. An Argumentative Review

Although early aggressive and prolonged treatment with specific antibiotics can extend survival in patients with cystic fibrosis (CF) colonized by opportunistic Pseudomonas aeruginosa (PA), antibiotics fail to eradicate the infecting multidrug-resistant (MDR) PA strains in CF. Century-long research has suggested treating patients with bacteriophages (phages, prokaryotic viruses) naturally hosted by bacteria. Although the only phage types used in therapy, lytic phages, lyse PA aggregated in biofilm matrix by depolymerase degrading enzymes, how they can effectively, safely, and persistently do so in patients with CF is unclear. Even though advanced techniques for formulating phage cocktails, training phages and collecting phage libraries have improved efficacy in vitro, whether personalized or ready-to-use therapeutic approaches or phages and antibiotics combined are effective and safe in vivo, and can reduce PA biofilms, remains debatable. Hence, to advance clinical research on phage therapy in clinical trials, also involving mucoid and non-mucoid multidrug-resistant PA in CF, and overcome problems in Western international regulations, we need reliable and repeatable information from experiments in vitro and in vivo on phage characterization, cocktail selection, personalized approaches, and phages combined with antibiotics. These findings, challenges, and promises prompted us to undertake this argumentative review to seek up-to-date information from papers describing lytic phage activity tested in vitro on PA laboratory strains, and PA strains from chronic infections including CF. We also reviewed in vivo studies on phage activity on pulmonary and non-pulmonary animal host models infected by laboratory or CF PA strains. Our argumentative review provides essential information showing that future phage clinical research in CF should use well-characterized and selected phages isolated against CF PA, tested in vitro under dynamic conditions in cocktails or combined with antibiotics, and in vivo on non-pulmonary and pulmonary host models infected with mucoid and non-mucoid CF MDR PA. Our findings should encourage pharmaceutical industries to conduct clinical trials in vitro and in vivo testing patented genomic engineered phages from phage libraries combined with antibiotics to treat or even prevent multidrug-resistant PA in CF, thus helping international regulatory agencies to plan future clinical research on phage therapy in CF.

Acceleration of the formation of biofilms on contact lens surfaces in the presence of neutrophil-derived cellular debris is conserved across multiple genera

Purpose

We have previously shown that invasive strains of Pseudomonas aeruginosa exploit the robust neutrophil response to form biofilms on contact lens surfaces and invade the corneal epithelium. The present study investigated the ability of multiple bacterial genera, all commonly recovered during contact lens-related infectious events, to adhere to and form biofilms on contact lens surfaces in the presence of neutrophils.

Methods

Five reference strains from the American Type Culture Collection were used: P. aeruginosa, Serratia marcescens, Stenotrophomonas maltophilia, Staphylococcus aureus, and Staphylococcus epidermidis. Each bacterial strain was incubated overnight with or without stimulated human neutrophils in the presence of an unworn contact lens. Standard colony counts and laser scanning confocal microscopy of BacLight-stained contact lenses were used to assess bacterial viability. Three-dimensional modeling of lens-associated biofilms with Imaris software was used to determine the biofilm volume. Lenses were further examined using scanning electron microscopy.

Results

Less than 1% of the starting inoculum adhered to the contact lens surface incubated with bacteria alone. There were no differences in adhesion rates to contact lens surfaces between bacteria in the absence of neutrophils for either the Gram-negative or Gram-positive test strains. Bacterial adhesion to contact lens surfaces was accelerated in the presence of human neutrophils for all test strains. This effect was least evident with S. epidermidis. There was also an increase in the number of viable bacteria recovered from contact lens surfaces (p<0.001 for the Gram-negative and Gram-positive test strains, respectively) and in biofilm volume (p<0.001 for the Gram-negative test strains, p = 0.005 for S. aureus).

Conclusions

These results show that in addition to P. aeruginosa, other bacteria commonly encountered during contact lens wear possess the capacity to utilize neutrophil-derived cellular debris to facilitate colonization of the lens surface. These data suggest that this phenomenon is conserved among multiple genera. Thus, during contact lens wear, the presence of inflammation and the accumulation of neutrophil debris under the posterior lens surface likely contribute to colonization of the lens. Further studies are needed to correlate these findings with risk for infection in an animal model.

Targeting polyelectrolyte networks in purulent body fluids to modulate bactericidal properties of some antibiotics

The response of the human immune system to most bacterial infections results in accumulation of neutrophils at infection sites that release a significant quantity of DNA and F-actin. Both are negatively charged polyelectrolytes that can interact with positively charged host defense molecules such as cathelicidin-delivered LL-37 peptide or other cationic antibiotic agents. Evaluation of the ability of bacterial outgrowth (using luminescence measurements or counting colony-forming units) to form a biofilm (quantified by crystal violet staining) and analysis of the structure of DNA/F-actin network by optical microscopy in human pus samples treated with different antibiotics in combination with plasma gelsolin, DNAse 1, and/or poly-aspartic acid revealed that bactericidal activity of most tested antibacterial agents increases in the presence of DNA/F-actin depolymerizing factors.

Therapeutic Potential of Biofilm-Dispersing Enzymes

Surface-attached colonies of bacteria known as biofilms play a major role in the pathogenesis of medical device infections. Biofilm colonies are notorious for their resistance to antibiotics and host defenses, which makes most device infections difficult or impossible to eradicate. Bacterial cells in a biofilm are held together by an extracellular polymeric matrix that is synthesized by the bacteria themselves. Enzymes that degrade biofilm matrix polymers have been shown to inhibit bio film formation, detach established bio film colonies, and render biofilm cells sensitive to killing by antimicrobial agents. This review discusses the potential use of biofilm matrix-degrading enzymes as anti-biofilm agents for the treatment and prevention of device infections. Two enzymes, deoxyribonuclease I and the glycoside hydrolase dispersin B, will be reviewed in detail. In vitro and in vivo studies demonstrating the anti-biofilm activities of these two enzymes will be summarized, and the therapeutic potential and possible drawbacks of using these enzymes as clinical agents will be discussed.

The Rationale and Evidence for Use of Inhaled Antibiotics to Control Pseudomonas aeruginosa Infection in Non-cystic Fibrosis Bronchiectasis

Non-cystic fibrosis bronchiectasis (NCFBE) is a chronic inflammatory lung disease characterized by irreversible dilation of the bronchi, symptoms of persistent cough and expectoration, and recurrent infective exacerbations. The prevalence of NCFBE is on the increase in the United States and Europe, but no licensed therapies are currently available for its treatment. Although there are many similarities between NCFBE and cystic fibrosis (CF) in terms of respiratory symptoms, airway microbiology, and disease progression, there are key differences, for example, in response to treatment, suggesting differences in pathogenesis. This review discusses possible reasons underlying differences in response to inhaled antibiotics in people with CF and NCFBE. Pseudomonas aeruginosa infections are associated with the most severe forms of bronchiectasis. Suboptimal levels of antibiotics in the lung increase the mutation frequency of P. aeruginosa and lead to the development of mucoid strains characterized by formation of a protective polysaccharide biofilm. Mucoid strains of P. aeruginosa are associated with a chronic infection stage, requiring long-term antibiotic therapy. Inhaled antibiotics provide targeted delivery to the lung with minimal systemic toxicity and adverse events compared with oral/intravenous routes of administration, and they could be alternative treatment options to help address some of the treatment challenges in the management of severe cases of NCFBE. This review provides an overview of completed and ongoing trials that evaluated inhaled antibiotic therapy for NCFBE. Recently, several investigators conducted phase 3 randomized controlled trials with inhaled aztreonam and ciprofloxacin in patients with NCFBE. While the aztreonam trial results were not associated with significant clinical benefit in NCFBE, initial results reported from the inhaled ciprofloxacin (dry powder for inhalation and liposome-encapsulated/dual-release formulations) trials hold promise. A more targeted approach could identify specific populations of NCFBE patients who benefit from inhaled antibiotics.

Macrophage migration inhibitory factor enhances Pseudomonas aeruginosa biofilm formation, potentially contributing to cystic fibrosis pathogenesis

Macrophage migration inhibitory factor (MIF) is a key proinflammatory mediator that we have previously shown to be associated with an aggressive clinical phenotype in cystic fibrosis. It possesses unique tautomerase enzymatic activity. However, to date, no human-derived substrate has been identified that has the capacity to interact with this cytokine's unique tautomerase activity. This led us to hypothesize that MIF may have the capacity to interact with external substrates. We describe for the first time how Pseudomonas aeruginosa can utilize human recombinant MIF (rMIF) to significantly (P < 0.01) enhance its endogenous biofilm formation. Our in vivo studies demonstrate that utilizing a small-molecular-weight inhibitor targeting MIF's tautomerase activity (SCD-19) significantly reduces the inflammatory response in a murine pulmonary chronic P. aeruginosa model. In addition, we show that in in vitro experiments, pretreatment of P. aeruginosa with rMIF is associated with reduced bacterial killing by tobramycin. Our novel findings support the concept of an anti-MIF strategy that targets this enzymatic activity as a potential future antibacterial therapeutic approach.-Tynan, A., Mawhinney, L., Armstrong, M. E., O'Reilly, C., Kennedy, S., Caraher, E., Jülicher, K., O'Dwyer, D., Maher, L., Schaffer, K., Fabre, A., McKone, E. F., Leng, L., Bucala, R., Bernhagen, J., Cooke, G., Donnelly, S. C. Macrophage migration inhibitory factor enhances Pseudomonas aeruginosa biofilm formation, potentially contributing to cystic fibrosis pathogenesis.

Mycobacterial Biofilms: Revisiting Tuberculosis Bacilli in Extracellular Necrotizing Lesions

Under detergent-free in vitro conditions, Mycobacterium tuberculosis, the etiological agent of tuberculosis in humans, spontaneously forms organized multicellular structures called biofilms. Moreover, in vitro biofilms of M. tuberculosis are more persistent against antibiotics than their single-cell planktonic counterparts, thereby raising questions about the occurrence of biofilms in the host tissues and their significance in persistence during chemotherapy of tuberculosis. In this article, we present arguments that extracellular M. tuberculosis in necrotizing lesions likely grows as biofilms.

Antimicrobial Efficacy of Contact Lens Care Solutions Against Neutrophil-Enhanced Bacterial Biofilms

Purpose

Neutrophil-derived extracellular debris has been shown to accelerate bacterial biofilm formation on hydrogel and silicone hydrogel contact lens surfaces compared to lenses inoculated with bacteria alone. The purpose of this study was to evaluate the disinfection efficacy of four standard commercial contact lens cleaning regimens against neutrophil-enhanced bacterial biofilms formed on silicone hydrogel contact lenses.

Methods

Four reference strains were used: Pseudomonas aeruginosa,Serratia marcescens,Stenotrophomonas maltophilia, and Staphylococcus aureus. Human neutrophils were isolated from peripheral blood by venipuncture. Unworn Lotrafilcon B lenses were incubated overnight in each respective strain with stimulated neutrophils. Contact lenses were then cleaned using one of four contact lens care solutions according to manufacturer instructions. Bacterial viability was assessed by colony counts and confocal microscopy. Volume of residual debris on lens surfaces after cleaning was quantified using IMARIS software.

Results

All four solutions tested showed effective antimicrobial activity against each bacterial strain; however, substantial amounts of nonviable bacteria and cellular debris remained on the lens surface despite concomitant digital cleaning.

Conclusions

Necrotic cellular debris that accumulates under the posterior lens surface during wear of an inoculated contact lens is not fully removed during routine cleaning and disinfection.

Translational Relevance

The accumulation of residual cellular debris on the contact lens surface may contribute to new colonization of the lens and represents a significant risk factor for a contact lens–related adverse event. Additional studies are needed to correlate these findings with risk for corneal infiltrative and/or infectious events in a standard animal model.

Biofilms and host response - helpful or harmful

Biofilm infections are one of the modern medical world's greatest challenges. Probably, all non-obligate intracellular bacteria and fungi can establish biofilms. In addition, there are numerous biofilm-related infections, both foreign body-related and non-foreign body-related. Although biofilm infections can present in numerous ways, one common feature is involvement of the host response with significant impact on the course. A special characteristic is the synergy of the innate and the acquired immune responses for the induced pathology. Here, we review the impact of the host response for the course of biofilm infections, with special focus on cystic fibrosis, chronic wounds and infective endocarditis.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.

A Critical Role for Extracellular DNA in Dental Plaque Formation

Extracellular DNA (eDNA) has been identified in the matrix of many different monospecies biofilms in vitro, including some of those produced by oral bacteria. In many cases, eDNA stabilizes the structure of monospecies biofilms. Here, the authors aimed to determine whether eDNA is an important component of natural, mixed-species oral biofilms, such as plaque on natural teeth or dental implants. To visualize eDNA in oral biofilms, approaches for fluorescently stained eDNA with either anti-DNA antibodies or an ultrasensitive cell-impermeant dye, YOYO-1, were first developed using Enterococcus faecalis, an organism that has previously been shown to produce extensive eDNA structures within biofilms. Oral biofilms were modelled as in vitro "microcosms" on glass coverslips inoculated with the natural microbial population of human saliva and cultured statically in artificial saliva medium. Using antibodies and YOYO-1, eDNA was found to be distributed throughout microcosm biofilms, and was particularly abundant in the immediate vicinity of cells. Similar arrangements of eDNA were detected in biofilms on crowns and overdenture abutments of dental implants that had been recovered from patients during the restorative phase of treatment, and in subgingival dental plaque of periodontitis patients, indicating that eDNA is a common component of natural oral biofilms. In model oral biofilms, treatment with a DNA-degrading enzyme, NucB from Bacillus licheniformis, strongly inhibited the accumulation of biofilms. The bacterial species diversity was significantly reduced by treatment with NucB and particularly strong reductions were observed in the abundance of anaerobic, proteolytic bacteria such as Peptostreptococcus, Porphyromonas and Prevotella. Preformed biofilms were not significantly reduced by NucB treatment, indicating that eDNA is more important or more exposed during the early stages of biofilm formation. Overall, these data demonstrate that dental plaque eDNA is potentially an important target for oral biofilm control.

Candidacidal Activity of Selected Ceragenins and Human Cathelicidin LL-37 in Experimental Settings Mimicking Infection Sites

Fungal infections, especially those caused by antibiotic resistant pathogens, have become a serious public health problem due to the growing number of immunocompromised patients, including those subjected to anticancer treatment or suffering from HIV infection. In this study we assessed fungicidal activity of the ceragenins CSA-13, CSA-131 and CSA-192 against four fluconazole–resistant Candida strains. We found that ceragenins activity against planktonic Candida cells was higher than activity of human LL-37 peptide and synthetic cationic peptide omiganan. Compared to LL-37 peptide, ceragenins in the presence of DNase I demonstrated an increased ability to kill DNA-induced Candida biofilm. Microscopy studies show that treatment with LL-37 or ceragenins causes Candida cells to undergo extensive surface changes indicating surface membrane damage. This conclusion was substantiated by observation of rapid incorporation of FITC-labeled CSA-13, CSA-131 or LL-37 peptide into the more lipophilic environment of the Candida membrane. In addition to activity against Candida spp., ceragenins CSA-131 and CSA-192 display strong fungicidal activity against sixteen clinical isolates including Cryptococcus neoformans and Aspergillus fumigatus. These results indicate the potential of ceragenins for future development as new fungicidal agents.

Exopolysaccharide biosynthetic glycoside hydrolases can be utilized to disrupt and prevent Pseudomonas aeruginosa biofilms

Bacterial biofilms present a significant medical challenge because they are recalcitrant to current therapeutic regimes. A key component of biofilm formation in the opportunistic human pathogen Pseudomonas aeruginosa is the biosynthesis of the exopolysaccharides Pel and Psl, which are involved in the formation and maintenance of the structural biofilm scaffold and protection against antimicrobials and host defenses. Given that the glycoside hydrolases PelAh and PslGh encoded in the pel and psl biosynthetic operons, respectively, are utilized for in vivo exopolysaccharide processing, we reasoned that these would provide specificity to target P. aeruginosa biofilms. Evaluating these enzymes as potential therapeutics, we demonstrate that these glycoside hydrolases selectively target and degrade the exopolysaccharide component of the biofilm matrix. PelAh and PslGh inhibit biofilm formation over a 24-hour period with a half maximal effective concentration (EC50) of 69.3 ± 1.2 and 4.1 ± 1.1 nM, respectively, and are capable of disrupting preexisting biofilms in 1 hour with EC50 of 35.7 ± 1.1 and 12.9 ± 1.1 nM, respectively. This treatment was effective against clinical and environmental P. aeruginosa isolates and reduced biofilm biomass by 58 to 94%. These noncytotoxic enzymes potentiated antibiotics because the addition of either enzyme to a sublethal concentration of colistin reduced viable bacterial counts by 2.5 orders of magnitude when used either prophylactically or on established 24-hour biofilms. In addition, PelAh was able to increase neutrophil killing by ~50%. This work illustrates the feasibility and benefits of using bacterial exopolysaccharide biosynthetic glycoside hydrolases to develop novel antibiofilm therapeutics.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

70th Anniversary Collection for the Microbiology Society: Journal of Medical Microbiology

In the last 70 years, we have seen a radical change in our perception and understanding of the microbial world. During this period, we learned from Woese and Fox there exists a third kingdom called 'Archea' based on the phylogenetic studies of the 16S rRNA that revolutionized microbiology (Woese & Fox, 1977; Woese et al., 1978). Furthermore, we were forced to reckon with the fact that Koch and Pasteur's way of growing cells in test-tubes or flasks planktonically does not necessarily translate to the real-life scenario of bacterial lifestyle, where they prefer to live and function as a closely knit microbial community called biofilm. Thanks are due to Costerton, who led the crusade on the concept of biofilms and expanded its scope of inquiry, which forced scientists and clinicians worldwide to rethink how we evaluate and apply the data. Then progressively, disbelief turned into belief, and now it is universally accepted that the micro-organisms hobnob with the members of their community to communicate and coordinate their behaviour, especially in regard to growth patterns and virulence traits via signalling molecules. Just when we thought that we were losing the battle against bacteria, antimicrobials were discovered. We then witnessed the rise and fall of antibiotics and the development of antibiotic resistance. Due to space and choice limitation, we will focus on the three areas that caused this major paradigm shift (i) antimicrobial resistance (AMR), (ii) biofilm and (iii) quorum sensing (QS), and how the Journal of Medical Microbiology played a major role in advancing the shift.

Residence in biofilms allows Burkholderia cepacia complex (Bcc) bacteria to evade the antimicrobial activities of neutrophil-like dHL60 cells

Bacteria of the Burkholderia cepacia complex (Bcc) persist in the airways of people with cystic fibrosis (CF) despite the continuous recruitment of neutrophils. Most members of Bcc are multidrug resistant and can form biofilms. As such, we sought to investigate whether biofilm formation plays a role in protecting Bcc bacteria from neutrophils. Using the neutrophil-like, differentiated cell line, dHL60, we have shown for the first time that Bcc biofilms are enhanced in the presence of these cells. Biofilm biomass was greater following culture in the presence of dHL60 cells than in their absence, likely the result of incorporating dHL60 cellular debris into the biofilm. Moreover, we have demonstrated that mature biofilms (cultured for up to 72 h) induced necrosis in the cells. Established biofilms also acted as a barrier to the migration of the cells and masked the bacteria from being recognized by the cells; dHL60 cells expressed less IL-8 mRNA and secreted significantly less IL-8 when cultured in the presence of biofilms, with respect to planktonic bacteria. Our findings provide evidence that biofilm formation can, at least partly, enable the persistence of Bcc bacteria in the CF airway and emphasize a requirement for anti-biofilm therapeutics.

How Biofilms Evade Host Defenses

The steps involved during the biofilm growth cycle include attachment to a substrate followed by more permanent adherence of the microorganisms, microcolony arrangement, and cell detachment required for the dissemination of single or clustered cells to other organ systems. Various methods have been developed for biofilm detection and quantitation. Biofilm-producing microorganisms can be detected in tissue culture plates, using silicone tubes and staining methods, and by visual assessment using scanning electron microscopy or confocal scanning laser microscopy. Quantitative measurement of biofilm growth is determined by using methods that include dry cell weight assays, colony-forming-unit counting, DNA quantification, or XTT 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide reduction assay. Upon infection, innate immune defense strategies are able to establish an immediate response through effector mechanisms mediated by immune cells, receptors, and several humoral factors. We present an overview of the life cycle of biofilms and their diversity, detection methods for biofilm development, and host immune responses to pathogens. We then focus on current concepts in bacterial and fungal biofilm immune evasion mechanisms. This appears to be of particular importance because the use of host immune responses may represent a novel therapeutic approach against biofilms.

How Biofilms Evade Host Defenses

The steps involved during the biofilm growth cycle include attachment to a substrate followed by more permanent adherence of the microorganisms, microcolony arrangement, and cell detachment required for the dissemination of single or clustered cells to other organ systems. Various methods have been developed for biofilm detection and quantitation. Biofilm-producing microorganisms can be detected in tissue culture plates, using silicone tubes and staining methods, and by visual assessment using scanning electron microscopy or confocal scanning laser microscopy. Quantitative measurement of biofilm growth is determined by using methods that include dry cell weight assays, colony-forming-unit counting, DNA quantification, or XTT 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide reduction assay. Upon infection, innate immune defense strategies are able to establish an immediate response through effector mechanisms mediated by immune cells, receptors, and several humoral factors. We present an overview of the life cycle of biofilms and their diversity, detection methods for biofilm development, and host immune responses to pathogens. We then focus on current concepts in bacterial and fungal biofilm immune evasion mechanisms. This appears to be of particular importance because the use of host immune responses may represent a novel therapeutic approach against biofilms.

Polyelectrolyte-mediated increase of biofilm mass formation

Background

Biofilm formation is associated with various aspects of bacterial and fungal infection. This study was designed to assess the impact of diverse natural polyelectrolytes, such as DNA, F-actin, neurofilaments (NFs), vimentin and purified Pf1 bacteriophage on biofilm formation and swarming motility of select pathogens including Pseudomonas aeruginosa associated with lung infections in CF patients.

Results

The bacteriophage Pf1 (1 mg/ml) significantly increased biofilm mass produced by Pseudomonas aeruginosa P14, Escherichia coli RS218 and Bacillus subtilis ATCC6051. DNA, F-actin, NFs and Pf1 also increased biofilm mass of the fungal C. albicans 1409 strain. Addition of F-actin, DNA or Pf1 bacteriophage to 0.5% agar plates increased swarming motility of Pseudomonas aeruginosa Xen5.

Conclusions

The presence of polyelectrolytes at infection sites is likely to promote biofilm growth and bacterial swarming.

The exopolysaccharide Psl-eDNA interaction enables the formation of a biofilm skeleton in Pseudomonas aeruginosa

A hallmark of bacterial biofilms is a self-produced extracellular matrix of exopolysaccharide, extracellular DNA (eDNA) and proteins that hold bacterial cells together in the community. However, interactions among matrix components and how the interactions contribute to the formation of matrix remain unclear. Here, we show the physical interaction between exopolysaccharide Psl and eDNA, the two key biofilm matrix components of the opportunistic pathogen Pseudomonas aeruginosa. The interaction allows the two components to combine to form a web of eDNA-Psl fibres, which resembles a biofilm skeleton in the centre of pellicles to give bacteria structural support and capability against agents targeted on one matrix component. The web of eDNA-Psl fibres was also found in flow-cell biofilms at microcolonies initiation stage. The colocalization of eDNA or Psl fibres with bacterial cell membrane stain suggests that fibre-like eDNA is likely derived from the lysis of dead bacteria in biofilms. Psl can interact with DNA from diverse sources, suggesting that P. aeruginosa has the ability to use DNA of other organisms (such as human neutrophils and other bacterial species) to form its own communities, which might increase the survival of P. aeruginosa in multispecies biofilms or within a human host.

A lipid mediator hepoxilin A3 is a natural inducer of neutrophil extracellular traps in human neutrophils

Pulmonary exacerbations in cystic fibrosis airways are accompanied by inflammation, neutrophilia, and mucous thickening. Cystic fibrosis sputum contains a large amount of uncleared DNA contributed by neutrophil extracellular trap (NET) formation from neutrophils. The exact mechanisms of the induction of NETosis in cystic fibrosis airways remain unclear, especially in uninfected lungs of patients with early cystic fibrosis lung disease. Here we show that Hepoxilin A3, a proinflammatory eicosanoid, and the synthetic analog of Hepoxilin B3, PBT-3, directly induce NETosis in human neutrophils. Furthermore, we show that Hepoxilin A3-mediated NETosis is NADPH-oxidase-dependent at lower doses of Hepoxilin A3, while it is NADPH-oxidase-independent at higher doses. Together, these results demonstrate that Hepoxilin A3 is a previously unrecognized inducer of NETosis in cystic fibrosis lungs and may represent a new therapeutic target for treating cystic fibrosis and other inflammatory lung diseases.

Pseudomonas aeruginosa biofilm infections: from molecular biofilm biology to new treatment possibilities

Bacteria in natural, industrial and clinical settings predominantly live in biofilms, i.e., sessile structured microbial communities encased in self-produced extracellular matrix material. One of the most important characteristics of microbial biofilms is that the resident bacteria display a remarkable increased tolerance toward antimicrobial attack. Biofilms formed by opportunistic pathogenic bacteria are involved in devastating persistent medical device-associated infections, and chronic infections in individuals who are immune-compromised or otherwise impaired in the host defense. Because the use of conventional antimicrobial compounds in many cases cannot eradicate biofilms, there is an urgent need to develop alternative measures to combat biofilm infections. The present review is focussed on the important opportunistic pathogen and biofilm model organism Pseudomonas aeruginosa. Initially, biofilm infections where P. aeruginosa plays an important role are described. Subsequently, current insights into the molecular mechanisms involved in P. aeruginosa biofilm formation and the associated antimicrobial tolerance are reviewed. And finally, based on our knowledge about molecular biofilm biology, a number of therapeutic strategies for combat of P. aeruginosa biofilm infections are presented.

Enhanced in vitro formation and antibiotic resistance of nonattached Pseudomonas aeruginosa aggregates through incorporation of neutrophil products

Pseudomonas aeruginosa is a major pathogen in cystic fibrosis (CF) lung disease. Children with CF are routinely exposed to P. aeruginosa from the natural environment, and by adulthood, 80% of patients are chronically infected. P. aeruginosa in the CF airway exhibits a unique biofilm-like structure, where it grows in small clusters or aggregates of bacteria in association with abundant polymers of neutrophil-derived components F-actin and DNA, among other components. These aggregates differ substantially in size and appearance compared to surface-attached in vitro biofilm models classically utilized for studies but are believed to share properties of surface-attached biofilms, including antibiotic resistance. However, little is known about the formation and function of surface-independent modes of biofilm growth, how they might be eradicated, and quorum sensing communication. To address these issues, we developed a novel in vitro model of P. aeruginosa aggregates incorporating human neutrophil-derived products. Aggregates grown in vitro and those found in CF patients' sputum samples were morphologically similar; viable bacteria were distributed in small pockets throughout the aggregate. The lasA quorum sensing gene was differentially expressed in the presence of neutrophil products. Importantly, aggregates formed in the presence of neutrophils acquired resistance to tobramycin, which was lost when the aggregates were dispersed with DNase, and antagonism of tobramycin and azithromycin was observed. This novel yet simple in vitro system advances our ability to model infection of the CF airway and will be an important tool to study virulence and test alternative eradication strategies against P. aeruginosa.

Pseudomonas aeruginosa infectious keratitis in a high oxygen transmissible rigid contact lens rabbit model

PURPOSE

To establish a rabbit model of infectious Pseudomonas aeruginosa keratitis using ultrahigh oxygen transmissible rigid lenses and characterize the frequency and severity of infection when compared to a non-oxygen transmissible lens material.

METHODS

Rabbits were fit with rigid lenses composed of ultrahigh and non-oxygen transmissible materials. Prior to wear, lenses were inoculated with an invasive corneal isolate of P. aeruginosa stably conjugated to green fluorescent protein (GFP). Corneas were examined before and after lens wear using a modified Heidelberg Rostock Tomograph in vivo confocal microscope. Viable bacteria adherent to unworn and worn lenses were assessed by standard plate counts. The presence of P. aeruginosa-GFP and myeloperoxidase-labeled neutrophils in infected corneal tissue was evaluated using laser scanning confocal microscopy.

RESULTS

The frequency and severity of infectious keratitis was significantly greater with inoculated ultrahigh oxygen transmissible lenses. Infection severity was associated with increasing neutrophil infiltration and in severe cases, corneal melting. In vivo confocal microscopic analysis of control corneas following lens wear confirmed that hypoxic lens wear was associated with mechanical surface damage, whereas no ocular surface damage was evident in the high-oxygen lens group.

CONCLUSIONS

These data indicate that in the absence of adequate tear clearance, the presence of P. aeruginosa trapped under the lens overrides the protective effects of oxygen on surface epithelial cells. These findings also suggest that alternative pathophysiological mechanisms exist whereby changes under the lens in the absence of frank hypoxic damage result in P. aeruginosa infection in the otherwise healthy corneal epithelium.

Pseudomonas aeruginosa biofilms: mechanisms of immune evasion

The opportunistic gram-negative bacterium Pseudomonas aeruginosa is implicated in many chronic infections and is readily isolated from chronic wounds, medical devices, and the lungs of cystic fibrosis patients. P. aeruginosa is believed to persist in the host organism due to its capacity to form biofilms, which protect the aggregated, biopolymer-embedded bacteria from the detrimental actions of antibiotic treatments and host immunity. A key component in the protection against innate immunity is rhamnolipid, which is a quorum sensing (QS)-regulated virulence factor. QS is a cell-to-cell signaling mechanism used to coordinate expression of virulence and protection of aggregated biofilm cells. Rhamnolipids are known for their ability to cause hemolysis and have been shown to cause lysis of several cellular components of the human immune system, for example, macrophages and polymorphonuclear leukocytes (PMNs). In this chapter, the interplay between P. aeruginosa and the PMNs in chronic infections is discussed with focus on the role of rhamnolipids and extracellular DNA.

Expression of antimicrobial drug tolerance by attached communities of Mycobacterium tuberculosis

There is an urgent need to improve methods used to screen antituberculosis drugs. An in vitro assay was developed to test drug treatment strategies that specifically target drug-tolerant Mycobacterium tuberculosis. The H37Rv strain of M. tuberculosis survived antimicrobial treatment as attached microbial communities when maintained in tissue culture media (RPMI-1640) with or without lysed human peripheral blood leukocytes. When cultured planktonically in the presence of Tween-80, bacilli failed to form microbial communities or reach logarithmic phase growth yet remained highly susceptible to antimicrobial drugs. In the absence of Tween, bacilli tolerated drug therapy by forming complex microbial communities attached to untreated well surfaces or to the extracellular matrix derived from lysed human leukocytes. Treatment of microbial communities with DNase I or Tween effectively dispersed bacilli and restored drug susceptibility. These data demonstrate that in vitro expression of drug tolerance by M. tuberculosis is linked to the establishment of attached microbial communities and that dispersion of bacilli targeting the extracellular matrix including DNA restores drug susceptibility. Modifications of this in vitro assay may prove beneficial in a high-throughput platform to screen new antituberculosis drugs especially those that target drug-tolerant bacilli.

Polyelectrolyte properties of filamentous biopolymers and their consequences in biological fluids

Anionic polyelectrolyte filaments are common in biological cells. DNA, RNA, the cytoskeletal filaments F-actin, microtubules, and intermediate filaments, and polysaccharides such as hyaluronan that form the pericellular matrix all have large net negative charge densities distributed over their surfaces. Several filamentous viruses with diameters and stiffnesses similar to those of cytoskeletal polymers also have similar negative charge densities. Extracellular protein filaments such collagen, fibrin and elastin, in contrast, have notably smaller charge densities and do not behave as highly charged polyelectrolytes in solution. This review summarizes data that demonstrate generic counterion-mediated effects on four structurally unrelated biopolymers of similar charge density: F-actin, vimentin, Pf1 virus, and DNA, and explores the possible biological and pathophysiological consequences of the polyelectrolyte properties of biological filaments.

Mycobacterium avium biofilm attenuates mononuclear phagocyte function by triggering hyperstimulation and apoptosis during early infection

Mycobacterium avium subsp. hominissuis is an opportunistic human pathogen that has been shown to form biofilm in vitro and in vivo. Biofilm formation in vivo appears to be associated with infections in the respiratory tract of the host. The reasoning behind how M. avium subsp. hominissuis biofilm is allowed to establish and persist without being cleared by the innate immune system is currently unknown. To identify the mechanism responsible for this, we developed an in vitro model using THP-1 human mononuclear phagocytes cocultured with established M. avium subsp. hominissuis biofilm and surveyed various aspects of the interaction, including phagocyte stimulation and response, bacterial killing, and apoptosis. M. avium subsp. hominissuis biofilm triggered robust tumor necrosis factor alpha (TNF-α) release from THP-1 cells as well as superoxide and nitric oxide production. Surprisingly, the hyperstimulated phagocytes did not effectively eliminate the cells of the biofilm, even when prestimulated with gamma interferon (IFN-γ) or TNF-α or cocultured with natural killer cells (which have been shown to induce anti-M. avium subsp. hominissuis activity when added to THP-1 cells infected with planktonic M. avium subsp. hominissuis). Time-lapse microscopy and the TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay determined that contact with the M. avium subsp. hominissuis biofilm led to early, widespread onset of apoptosis, which is not seen until much later in planktonic M. avium subsp. hominissuis infection. Blocking TNF-α or TNF-R1 during interaction with the biofilm significantly reduced THP-1 apoptosis but did not lead to elimination of M. avium subsp. hominissuis. Our data collectively indicate that M. avium subsp. hominissuis biofilm induces TNF-α-driven hyperstimulation and apoptosis of surveilling phagocytes, which prevents clearance of the biofilm by cells of the innate immune system and allows the biofilm-associated infection to persist.

Biofilm matrix and its regulation in Pseudomonas aeruginosa

Biofilms are communities of microorganisms embedded in extracellular polymeric substances (EPS) matrix. Bacteria in biofilms demonstrate distinct features from their free-living planktonic counterparts, such as different physiology and high resistance to immune system and antibiotics that render biofilm a source of chronic and persistent infections. A deeper understanding of biofilms will ultimately provide insights into the development of alternative treatment for biofilm infections. The opportunistic pathogen Pseudomonas aeruginosa, a model bacterium for biofilm research, is notorious for its ability to cause chronic infections by its high level of drug resistance involving the formation of biofilms. In this review, we summarize recent advances in biofilm formation, focusing on the biofilm matrix and its regulation in P. aeruginosa, aiming to provide resources for the understanding and control of bacterial biofilms.