NF-κB-Signaling-Targeted Immunomodulatory Nanoparticle with Photothermal and Quorum-Sensing Inhibition Effects for Efficient Healing of Biofilm-Infected Wounds

The development of therapeutics with high antimicrobial activity and immunomodulatory effects is urgently needed for the treatment of infected wounds due to the increasing danger posed by recalcitrant-infected wounds. In this study, we developed light-controlled antibacterial, photothermal, and immunomodulatory biomimetic N/hPDA@M nanoparticles (NPs). This nanoplatform was developed by loading flavonoid naringenin onto hollow mesoporous polydopamine NPs in a π-π-stacked configuration and encasing them with macrophage membranes. First, our N/hPDA@M NPs efficiently neutralized inflammatory factors present within the wound microenvironment by the integration of macrophage membranes. Afterward, the N/hPDA@M NPs effectively dismantled bacterial biofilms through a combination of the photothermal properties of PDA and the quorum sensing inhibitory effects of naringenin. It is worth noting that N/hPDA@M NPs near-infrared-enhanced release of naringenin exhibited specificity toward the NF-κB-signaling pathway, effectively mitigating the inflammatory response. This innovative design not only conferred remarkable antibacterial properties upon the N/hPDA@M NPs but also endowed them with the capacity to modulate inflammatory responses, curbing excessive inflammation and steering macrophage polarization toward the M2 phenotype. As a result, this multifaceted approach significantly contributes to expediting the healing process of infected skin wounds.

Biofilm exopolysaccharides alter sensory-neuron-mediated sickness during lung infection

Infections of the lung cause observable sickness thought to be secondary to inflammation. Signs of sickness are crucial to alert others via behavioral-immune responses to limit contact with contagious individuals. Gram-negative bacteria produce exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on sickness remains uncertain. Using genome-engineered Pseudomonas aeruginosa (P. aeruginosa) strains, we compared EPS-producers versus non-producers and a virulent Escherichia coli (E. coli) lung infection model in male and female mice. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness, behavioral alterations, inflammation, and hypothermia mediated by TLR4 detection of the exposed lipopolysaccharide (LPS) in lung TRPV1+ sensory neurons. However, inflammation did not account for sickness. Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Thus, EPS-producing biofilm pathogens evade initiating a lung-brain sensory neuronal response that results in sickness.

Strategies to Promote the Journey of Nanoparticles Against Biofilm-Associated Infections

Biofilm-associated infections are one of the most challenging healthcare threats for humans, accounting for 80% of bacterial infections, leading to persistent and chronic infections. The conventional antibiotics still face their dilemma of poor therapeutic effects due to the high tolerance and resistance led by bacterial biofilm barriers. Nanotechnology-based antimicrobials, nanoparticles (NPs), are paid attention extensively and considered as promising alternative. This review focuses on the whole journey of NPs against biofilm-associated infections, and to clarify it clearly, the journey is divided into four processes in sequence as 1) Targeting biofilms, 2) Penetrating biofilm barrier, 3) Attaching to bacterial cells, and 4) Translocating through bacterial cell envelope. Through outlining the compositions and properties of biofilms and bacteria cells, recent advances and present the strategies of each process are comprehensively discussed to combat biofilm-associated infections, as well as the combined strategies against these infections with drug resistance, aiming to guide the rational design and facilitate wide application of NPs in biofilm-associated infections.

Bacterial Biofilm Formation on Biomaterials and Approaches to Its Treatment and Prevention

Bacterial biofilms can cause widespread infection. In addition to causing urinary tract infections and pulmonary infections in patients with cystic fibrosis, biofilms can help microorganisms adhere to the surfaces of various medical devices, causing biofilm-associated infections on the surfaces of biomaterials such as venous ducts, joint prostheses, mechanical heart valves, and catheters. Biofilms provide a protective barrier for bacteria and provide resistance to antimicrobial agents, which increases the morbidity and mortality of patients. This review summarizes biofilm formation processes and resistance mechanisms, as well as the main features of clinically persistent infections caused by biofilms. Considering the various infections caused by clinical medical devices, we introduce two main methods to prevent and treat biomaterial-related biofilm infection: antibacterial coatings and the surface modification of biomaterials. Antibacterial coatings depend on the covalent immobilization of antimicrobial agents on the coating surface and drug release to prevent and combat infection, while the surface modification of biomaterials affects the adhesion behavior of cells on the surfaces of implants and the subsequent biofilm formation process by altering the physical and chemical properties of the implant material surface. The advantages of each strategy in terms of their antibacterial effect, biocompatibility, limitations, and application prospects are analyzed, providing ideas and research directions for the development of novel biofilm infection strategies related to therapeutic materials.

Combating Bacterial Biofilms: Current and Emerging Antibiofilm Strategies for Treating Persistent Infections

Biofilms are intricate multicellular structures created by microorganisms on living (biotic) or nonliving (abiotic) surfaces. Medically, biofilms often lead to persistent infections, increased antibiotic resistance, and recurrence of infections. In this review, we highlighted the clinical problem associated with biofilm infections and focused on current and emerging antibiofilm strategies. These strategies are often directed at disrupting quorum sensing, which is crucial for biofilm formation, preventing bacterial adhesion to surfaces, impeding bacterial aggregation in viscous mucus layers, degrading the extracellular polymeric matrix, and developing nanoparticle-based antimicrobial drug complexes which target persistent cells within the biofilm core. It is important to acknowledge, however, that the use of antibiofilm agents faces obstacles, such as limited effectiveness in vivo, potential cytotoxicity to host cells, and propensity to elicit resistance in targeted biofilm-forming microbes. Emerging next generation antibiofilm strategies, which rely on multipronged approaches, were highlighted, and these benefit from current advances in nanotechnology, synthetic biology, and antimicrobial drug discovery. The assessment of current antibiofilm mitigation approaches, as presented here, could guide future initiatives toward innovative antibiofilm therapeutic strategies. Enhancing the efficacy and specificity of some emerging antibiofilm strategies via careful investigations, under conditions that closely mimic biofilm characteristics within the human body, could bridge the gap between laboratory research and practical application.

Challenges faced in developing an ideal chronic wound model

INTRODUCTION

Chronic wounds are a major drain on healthcare resources and can lead to substantial reductions in quality of life for those affected. Moreover, they often precede serious events such as limb amputations and premature death. In the long run, this burden is likely to escalate with an ageing population and lifestyle diseases such as obesity. Thus far, the identification of beneficial therapeutics against chronic wounds have been hindered by the lack of an ideal chronic wound animal model. Although animal models of delayed healing have been developed, none of these models fully recapitulate the complexity of the human chronic wound condition. Furthermore, most animals do not develop chronic wounds. Only the thoroughbred racehorse develops chronic ulcers.

AREAS COVERED

In this review, the different characteristics of chronic wounds that highlight its complexity are described. In addition, currently available models reflecting different aspects of chronic wound pathology and their relevance to human chronic wounds are discussed. This article concludes by listing relevant features representative of an ideal chronic wound model. Additionally, alternative approaches for the development of chronic wound models are discussed.

EXPERT OPINION

Delayed models of healing, including the streptozotocin diabetic model, skin flap model and magnet-induced IR models have emerged. While these models have been widely adopted for preclinical therapeutic testing, their relevance towards human chronic wounds remains debatable. In particular, current delayed healing models often fail to fully incorporate the key characteristics of chronic ulcers. Ultimately, more representative models are required to expedite the advancement of novel therapeutics to the clinic.

Electrochemical Sensors Based on MoSx -Functionalized Laser-Induced Graphene for Real-Time Monitoring of Phenazines Produced by Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen causing infections in blood and implanted devices. Traditional identification methods take more than 24 h to produce results. Molecular biology methods expedite detection, but require an advanced skill set. To address these challenges, this work demonstrates functionalization of laser-induced graphene (LIG) for developing flexible electrochemical sensors for P. aeruginosa based on phenazines. Electrodeposition as a facile approach is used to functionalize LIG with molybdenum polysulfide (MoSx ). The sensor's limit of detection (LOD), sensitivity, and specificity are determined in broth, agar, and wound simulating medium (WSM). Control experiments with Escherichia coli, which does not produce phenazines, demonstrate specificity of sensors for P. aeruginosa. The LOD for pyocyanin (PYO) and phenazine-1-carboxylic acid (PCA) is 0.19 × 10-6  and 1.2 × 10-6  m, respectively. Furthermore, the highly stable sensors enable real-time monitoring of P. aeruginosa biofilms over several days. Comparing square wave voltammetry data over time shows time-dependent generation of phenazines. In particular, two configurations-"Normal" and "Flipped"-are studied, showing that the phenazines time dynamics vary depending on how cells interact with sensors. The reported results demonstrate the potential of the developed sensors for integration with wound dressings for early diagnosis of P. aeruginosa infection.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

In Vivo Biofilm Formation of Pathogenic Leptospira spp. in the Vitreous Humor of Horses with Recurrent Uveitis

Equine recurrent uveitis (ERU) causes painful inflammatory attacks and oftentimes blindness in the affected eyes. The disease is considered a late sequela of systemic leptospirosis. The most effective therapy is the surgical removal of the vitreous (vitrectomy), which is not only therapeutic, but provides vitreous material that can be assessed diagnostically. For example, the lipL32 gene, culturable Leptospira spp., and anti-Leptospira antibodies have all been detected in vitreous samples obtained from eyes with chronic ERU. Despite this clear evidence of leptospiral involvement, the systemic administration of antibiotics in infected horses is ineffective at resolving ERU. This syndrome of chronic recurrent inflammation, which is unresponsive to antibiotic therapy, combined with apparent bacteria evading the immune response, is consistent with a biofilm-associated infection. The purpose of this study, therefore, was to detect the in vivo biofilm formation of Leptospira spp. in vitreous samples collected during vitrectomy and examined using a Warthin-Starry silver stain and immunohistochemistry. All known steps of biofilm formation were visualized in these samples, including individual Leptospira spp., leptospiral microcolonies and dense roundish accumulations of Leptospira spp. In many instances spirochetes were surrounded by an extracellular substance. Taken together, data from the present study show that ERU is a biofilm-associated intraocular leptospiral infection, which best explains the typical clinical course.

Adjunctive Use of Phage Sb-1 in Antibiotics Enhances Inhibitory Biofilm Growth Activity versus Rifampin-Resistant Staphylococcus aureus Strains

Effective antimicrobials are crucial for managing Staphylococcus aureus implant-associated bone infections (IABIs), particularly for infections due to rifampin-resistant S. aureus (RRSA). Failure to remove the implant results in persistent infection; thus, prolonged suppressive antibiotic therapy may be a reasonable alternative. However, a high incidence of adverse events can necessitate the discontinuation of therapy. In this scenario, commercial Staphylococcal bacteriophage Sb-1 combined with antibiotics is an option, showing a promising synergistic activity to facilitate the treatment of biofilm infections. Therefore, we evaluated the efficacy of the inhibitory activity of five antibiotics (doxycycline, levofloxacin, clindamycin, linezolid, and rifampin) alone or combined with phage Sb-1 (10⁶ PFU/mL) in a simultaneous and staggered manner, to combat five clinical RRSA strains and the laboratory strain MRSA ATCC 43300 in 72 h by isothermal microcalorimetry. The synergistic effects were observed when phage Sb-1 (10⁶ PFU/mL) combined with antibiotics had at least 2 log-reduction lower concentrations, represented by a fractional biofilm inhibitory concentration (FBIC) of <0.25. Among the antibiotics that we tested, the synergistic effect of all six strains was achieved in phage/doxycycline and phage/linezolid combinations in a staggered manner, whereas a distinctly noticeable improvement in inhibitory activity was observed in the phage/doxycycline combination with a low concentration of doxycycline. Moreover, phage/levofloxacin and phage/clindamycin combinations also showed a synergistic inhibitory effect against five strains and four strains, respectively. Interestingly, the synergistic inhibitory activity was also observed in the doxycycline-resistant and levofloxacin-resistant profile strains. However, no inhibitory activity was observed for all of the combinations in a simultaneous manner, as well as for the phage/rifampin combination in a staggered manner. These results have implications for alternative, combined, and prolonged suppressive antimicrobial treatment approaches.

Near-Infrared Light Triggered Phototherapy and Immunotherapy for Elimination of Methicillin-Resistant Staphylococcus aureus Biofilm Infection on Bone Implant

Clinically, methicillin-resistant Staphylococcus aureus (MRSA) biofilm infection inevitably induces the failure of bone implants. Herein, a hydrophilic and viscous hydrogel of poly(vinyl alcohol) modified with chitosan, polydopamine, and NO release donor was formed on a red phosphorus nanofilm deposited on a titanium implant (Ti-RP/PCP/RSNO). Under the irradiation of near-infrared light (NIR), peroxynitrite (^•ONOO^-) was formed by the reaction between the released NO and superoxide (^•O₂^-) produced by the RP nanofilm. Specifically, we revealed the antibacterial mechanism of the ONOO^- against the MRSA biofilm. In addition, osteogenic differentiation was promoted and inflammatory polarization was regulated by the released NO without NIR irradiation through upregulating the expression of Opn and Ocn genes and TNF-α. The MRSA biofilm was synergistically eradicated by ^•ONOO^-, hyperthermia, and ^•O^2- under NIR irradiation as well as the immunoreaction of the M1 polarization. The in vivo results also confirmed the excellent osteogenesis and biofilm eradication by released NO from the RP/PCP/RSNO system under NIR irradiation, indicating the noninvasive tissue reconstruction of MRSA-infected tissues through phototherapy and immunotherapy.

Clinically Relevant Epithelial Lining Fluid Concentrations of Meropenem with Ciprofloxacin Provide Synergistic Killing and Resistance Suppression of Hypermutable Pseudomonas aeruginosa in a Dynamic Biofilm Model

Treatment of exacerbations of chronic Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) is highly challenging due to hypermutability, biofilm formation, and an increased risk of resistance emergence. We evaluated the impact of ciprofloxacin and meropenem as monotherapy and in combination in the dynamic in vitro CDC biofilm reactor (CBR). Two hypermutable P. aeruginosa strains, PAOΔmutS (MIC of ciprofloxacin [MIC_{ciprofloxacin}], 0.25 mg/liter; MIC_meropenem, 2 mg/liter) and CW44 (MIC_{ciprofloxacin}, 0.5 mg/liter; MIC_meropenem, 4 mg/liter), were investigated for 120 h. Concentration-time profiles achievable in epithelial lining fluid (ELF) following FDA-approved doses were simulated in the CBR. Treatments were ciprofloxacin at 0.4 g every 8 h as 1-h infusions (80% ELF penetration), meropenem at 6 g/day as a continuous infusion (CI) (30% and 60% ELF penetration), and their combinations. Counts of total and less-susceptible planktonic and biofilm bacteria and MICs were determined. Antibiotic concentrations were quantified by an ultrahigh-performance liquid chromatography photodiode array (UHPLC-PDA) assay. For both strains, all monotherapies failed, with substantial regrowth and resistance of planktonic (≥8 log₁₀ CFU/ml) and biofilm (>8 log₁₀ CFU/cm²) bacteria at 120 h (MIC_{ciprofloxacin}, up to 8 mg/liter; MIC_meropenem, up to 64 mg/liter). Both combination treatments demonstrated synergistic bacterial killing of planktonic and biofilm bacteria of both strains from ∼48 h onwards and suppressed regrowth to ≤4 log₁₀ CFU/ml and ≤6 log₁₀ CFU/cm² at 120 h. Overall, both combination treatments suppressed the amplification of resistance of planktonic bacteria for both strains and of biofilm bacteria for CW44. The combination with meropenem at 60% ELF penetration also suppressed the amplification of resistance of biofilm bacteria for PAOΔmutS Thus, combination treatment demonstrated synergistic bacterial killing and resistance suppression against difficult-to-treat hypermutable P. aeruginosa strains.

Fighting Mixed-Species Microbial Biofilms With Cold Atmospheric Plasma

Most biofilms in nature are formed by multiple microbial species, and such mixed-species biofilms represent the actual lifestyles of microbes, including bacteria, fungi, viruses (phages), and/or protozoa. Microorganisms cooperate and compete in mixed-species biofilms. Mixed-species biofilm formation and environmental resistance are major threats to water supply, food industry, and human health. The methods commonly used for microbial eradication, such as antibiotic or disinfectant treatments, are often ineffective for mixed-species biofilm consortia due to their physical matrix barrier and physiological interactions. For the last decade, an increasing number of investigations have been devoted to the usage of cold atmospheric plasma (CAP), which is produced by dielectric barrier discharges or plasma jets to prevent or eliminate microbial biofilms. Here, we summarized the production of CAP, the inactivation of microorganisms upon CAP treatment, and the microbial factors affecting the efficacy of CAP procedure. The applications of CAP as antibiotic alternative strategies for fighting mixed-species biofilms were also addressed.

Scan Parameter Optimization for Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh

There is a critical need to develop new noninvasive therapies to treat bacteria biofilms. Previous studies have demonstrated the effectiveness of cavitation-based ultrasound histotripsy to destroy these biofilms. In this study, the dependence of biofilm destruction on multiple scan parameters was assessed by conducting exposures at different scan speeds (0.3-1.4 beamwidths/s), step sizes (0.25-0.5 beamwidths), and the number of passes of the focus across the mesh (2-6). For each of the exposure conditions, the number of colony-forming units (CFUs) remaining on the mesh was quantified. A regression analysis was then conducted, revealing that the scan speed was the most critical parameter for biofilm destruction. Reducing the number of passes and the scan speed should allow for more efficient biofilm destruction in the future, reducing the treatment time.

3D Bioprinted Scaffolds Containing Viable Macrophages and Antibiotics Promote Clearance of Staphylococcus aureus Craniotomy-Associated Biofilm Infection

Craniotomy involves the removal of a skull fragment to access the brain, such as during tumor or epilepsy surgery, which is immediately replaced intraoperatively. The infection incidence after craniotomy ranges from 0.8 to 3%, with approximately half caused by Staphylococcus aureus ( S. aureus). To mitigate infectious complications following craniotomy, we engineered a three-dimensional (3D) bioprinted bone scaffold to harness the potent antibacterial activity of macrophages (MΦs) together with antibiotics using a mouse S. aureus craniotomy-associated biofilm model that establishes a persistent infection on the bone flap, subcutaneous galea, and brain. The 3D scaffold contained rifampin and daptomycin printed in a composite slurry, with viable MΦs incorporated into a hydrogel-based bioink, which was assessed for both the treatment and prevention of craniotomy-associated infections in the mouse model. For the treatment paradigm, the bone flap was removed at day 7 post infection after a mature biofilm had formed and was replaced with a 3D printed antibiotic scaffold, with or without MΦ incorporation. Bacterial burdens in the galea and brain were reduced by at least 100-fold at early time points, which was potentiated by bioprinting viable MΦs into the 3D antibiotic scaffold. We also examined a prevention paradigm, where the scaffolds were placed at the time of surgery and challenged with S. aureus one day later at the surgical site. Interestingly, unlike the treatment paradigm, the incorporation of viable MΦs into the 3D antibiotic scaffold did not enhance bacterial clearance compared to that of antibiotic alone. With further refinement, our 3D bioprinted scaffold represents a potential treatment modality, as it delivers therapeutic antibiotic levels more rapidly than systemic administration, based on its proximity to the infection site. In addition, the incorporation of viable MΦs into the 3D scaffold is an important advance, which demonstrated an improved therapeutic benefit for the treatment of established biofilms that represent the most clinically challenging scenario.

Cardiac Implantable Electronic Device-Related Infection Due to Granulicatella adiacens

Cardiac implantable electronic device–related infection is clinically challenging. Curative treatment commonly includes system removal. A case caused by Granulicatella adiacens occurred in a 32-year-old woman. Clinical course, literature review, and biofilm investigations enabled successful antibiotic management without system removal.

Impact of High-Intensity Ultrasound on Strength of Surgical Mesh When Treating Biofilm Infections

The use of cavitation-based ultrasound histotripsy to treat infections on surgical mesh has shown great potential. However, any impact of the therapy on the mesh must be assessed before the therapy can be applied in the clinic. The goal of this study was to determine if the cavitation-based therapy would reduce the strength of the mesh thus compromising the functionality of the mesh. First, Staphylococcus aureus biofilms were grown on the surgical mesh samples and exposed to high-intensity ultrasound pulses. For each exposure, the effectiveness of the therapy was confirmed by counting the number of colony forming units (CFUs) on the mesh. Most of the exposed meshes had no CFUs with an average reduction of 5.4-log₁₀ relative to the sham exposures. To quantify the impact of the exposure on mesh strength, the force required to tear the mesh and the maximum mesh expansion before damage were quantified for control, sham, and exposed mesh samples. There was no statistical difference between the exposed and sham/control mesh samples in terms of ultimate tensile strength and corresponding mesh expansion. The only statistical difference was with respect to mesh orientation relative to the applied load. The tensile strength increased by 1.36 N while the expansion was reduced by 1.33 mm between different mesh orientations.

Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh Samples Under Varying Scan Parameters

Cavitation-based ultrasound histotripsy has shown potential for treating infections on surgical mesh. The goal of this paper was to explore a new scan strategy while assessing the impact of scan speed, scan step size, and the number of cycles in the tone burst on the destruction of S. aureus biofilms grown on surgical mesh samples using ultrasound histotripsy pulses (150 MPa/-17 MPa). For each exposure, the number of colony forming units (CFUs) on the mesh and released onto the surrounding gel was quantified. Most of the exposed mesh samples had no CFUs, and there was a statistically significant reduction in CFUs on the mesh for each of the exposures, with an average reduction of 3.8 log₁₀ relative to the sham. Compared with the sham, there was also a statistically significant reduction in CFUs on the gel with the highest exposures.

Chronic Pseudomonas aeruginosa biofilm infection impairs murine S100A8/A9 and neutrophil effector cytokines-implications for delayed wound closure?

The impact of Pseudomonas aeruginosa biofilm infections in chronic wounds and clinical implication for healing is receiving increased attention. However, the pathophysiology of host/pathogen interplay is not fully understood. By further revealing the mechanisms, necessary new treatment strategies may be identified. Since the background for chronic wounds is diverse, representative animal models are important. We assessed host response and spontaneous wound closure in the relatively resistant C3H/HeN and the susceptible BALB/c mouse strain. Full-thickness burn wounds were inflicted in 108 mice. Pseudomonas aeruginosa biofilm (106 colony forming units) was injected subcutaneously in 72 mice, euthanised day 4, 7 or 10 days post-infection. Wounds were analysed for neutrophil host response markers: S100A8/A9, keratinocyte-derived chemokine and granulocyte-colony stimulating factor. Total peripheral blood leucocyte and polymorphonuclear count were assessed in parallel. Histopathology evaluated wound inflammatory burden. Photoplanimetry described macroscopical wound closure. Stable chronic wound infection was established in all challenged mice. Pseudomonas aeruginosa biofilm suppressed neutrophil host response in wounds. C3H/HeN mice achieved earlier systemic inflammatory control and healed faster than BALB/c mice. Pseudomonas aeruginosa biofilms perturb host defence thereby inducing a steady state of chronic infection which may impair wound healing. These results indicate therapeutic options for immune modulation of biofilm-infected wounds.

Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh Samples Under Varying Pulse Durations

Prior studies demonstrated that histotripsy generated by high-intensity tone bursts to excite a bubble cloud adjacent to a medical implant can destroy the bacteria biofilm responsible for the infection. The goal of this paper was to treat Staphylococcus aureus (S. aureus) biofilms on surgical mesh samples while varying the number of cycles in the tone burst to minimize collateral tissue damage while maximizing therapy effectiveness. S. aureus biofilms were grown on 1-cm square surgical mesh samples. The biofilms were then treated in vitro using a spherically focused transducer (1.1 MHz, 12.9-cm focal length, 12.7-cm diameter) using either a sham exposure or histotripsy pulses with tone burst durations of 3, 5, or 10 cycles (pulse repetition frequency of 333 Hz, peak compressional pressure of 150 MPa, peak rarefactional pressure of 17 MPa). After treatment, the number of colony forming units (CFUs) on the mesh and the surrounding gel was independently determined. The number of CFUs remaining on the mesh for the sham exposure (4.8 ± 0.9-log₁₀) (sample mean ± sample standard deviation-log10 from 15 observations) was statistically significantly different from the 3-cycle (1.9 ± 1.5-log₁₀), 5-cycle (2.2 ± 1.1-log₁₀), and 10-cycle exposures (1 ± 1.5-log₁₀) with an average reduction in the number of CFUs of 3.1-log₁₀. The numbers of CFUs released into the gel for both the sham and exposure groups were the same within a bound of 0.86-log₁₀, but this interval was too large to deduce the fate of the bacteria in the biofilm following the treatment.

Surgical site infections following instrumented stabilization of the spine

Background

Implant-associated infections are still a feared complication in the field of orthopedics. Bacteria attach to the implant surface and form so-called biofilm colonies that are often difficult to diagnose and treat. Since the majority of studies focus on prosthetic joint infections (PJIs) of the hip and knee, current treatment options (eg, antibiotic prophylaxis) of implant-associated infections have mostly been adapted according to these results.

Objective

The aim of this study was to evaluate patients with surgical site infections following instrumented stabilization of the spine with regard to detected bacteria species and the course of the disease.

Patients and methods

We performed a retrospective single-center analysis of implant-associated infections of the spine from 2010 to 2014. A total of 138 patients were included in the study. The following parameters were evaluated: C-reactive protein serum concentration, microbiological evaluation of tissue samples, the time course of the disease, indication for instrumented stabilization of the spine, localization of the infection, and the number of revision surgeries required until cessation of symptoms.

Results

Coagulase-negative Staphylococcus spp. were most commonly detected (n=69, 50%), followed by fecal bacteria (n=46, 33.3%). In 23.2% of cases, no bacteria were detected despite clinical suspicion of an infection. Most patients suffered from degenerative spine disorders (44.9%), followed by spinal fractures (23.9%), non-degenerative scoliosis (20.3%), and spinal tumors (10.1%). Surgical site infections occurred predominantly within 3 months (64.5%), late infections after 2 years were rare (4.3%), in particular when compared with PJIs. Most cases were successfully treated after 1 revision surgery (60.9%), but there were significant differences between bacteria species. Fecal bacteria were more difficult to treat and often required more than 1 revision surgery.

Conclusion

In summary, we were able to demonstrate significant differences between spinal implant-associated infections and PJIs. These aspects should be considered early on in the treatment of surgical site infections following instrumented stabilization of the spine.

Immune Modulating Topical S100A8/A9 Inhibits Growth of Pseudomonas aeruginosa and Mitigates Biofilm Infection in Chronic Wounds

Pseudomonas aeruginosa biofilm maintains and perturbs local host defense, hindering timely wound healing. Previously, we showed that P. aeruginosa suppressed S100A8/A9 of the murine innate host defense. We assessed the potential antimicrobial effect of S100A8/A9 on biofilm-infected wounds in a murine model and P. aeruginosa growth in vitro. Seventy-six mice, inflicted with a full-thickness burn wound were challenged subcutaneously (s.c.) by 10⁶ colony-forming units (CFUs) of P. aeruginosa biofilm. Mice were subsequently randomized into two treatment groups, one group receiving recombinant murine S100A8/A9 and a group of vehicle controls (phosphate-buffered saline, PBS) all treated with s.c. injections daily for up to five days. Wounds were analyzed for quantitative bacteriology and contents of key inflammatory markers. Count of blood polymorphonuclear leukocytes was included. S100A8/A9-treatment ameliorated wound infection, as evaluated by quantitative bacteriology (p ≤ 0.05). In vitro, growth of P. aeruginosa was inhibited dose-dependently by S100A8/A9 in concentrations from 5 to 40 μg/mL, as determined by optical density-measurement (OD-measurement) and quantitative bacteriology. Treatment slightly augmented key inflammatory cytokine Tumor Necrosis Factor-α (TNF-α), but dampened interferon-γ (IFN-γ) levels and blood polymorphonuclear count. In conclusion, topical S100A8/A9 displays remarkable novel immune stimulatory and anti-infective properties in vivo and in vitro. Importantly, treatment by S100A8/A9 provides local infection control. Implications for a role as adjunctive treatment in healing of chronic biofilm-infected wounds are discussed.

Diagnosis of biofilm infections in cystic fibrosis patients

Chronic Pseudomonas aeruginosa biofilm lung infection in cystic fibrosis patients is the best described biofilm infection in medicine. The initial focus can be the paranasal sinuses and then follows repeated colonization and infection of the lungs by aspiration. The matrix of the biofilms is dominated by alginate and the pathogenesis of tissue damage is immune complex-mediated chronic inflammation dominated by polymorphonuclear leukocytes and their products (DNA, oxygen radicals and proteases). The P. aeruginosa biofilm infection can be diagnosed by microscopy of lung tissue, sputum and mucus from the paranasal sinuses, where aggregates of the bacteria are found surrounded by the abundant alginate matrix. Specific PNA-FISH probes can be used to identify P. aeruginosa and other pathogens in situ in the biofilms. Growth of mucoid colonies from the locations mentioned above is also diagnostic for biofilm infection. Rise of specific anti-P. aeruginosa antibodies is likewise diagnostic, IgG in serum in case of lung infection, sIgA in saliva or nasal secretions in case of paranasal sinus infection. Similar approaches have been developed to diagnose chronic biofilm infections in cystic fibrosis caused by other pathogens e.g., Stenotrophomonas, Burkholderia multivorans, Achromobacter xylosoxidans and Mycobacterium abscessus complex.

Going beyond the Control of Quorum-Sensing to Combat Biofilm Infections

Most bacteria attach to surfaces where they form a biofilm, cells embedded in a complex matrix of polymers. Cells in biofilms are much better protected against noxious agents than free-living cells. As a consequence it is very difficult to control pathogens with antibiotics in biofilm infections and novel targets are urgently needed. One approach aims at the communication between cells to form and to maintain a biofilm, a process called quorum-sensing. Water soluble small-sized molecules mediate this process and a number of antagonists of these compounds have been found. In this review natural compounds and synthetic drugs which do not interfere with the classical quorum-sensing compounds are discussed. For some of these compounds the targets are still not known, but others interfere with the formation of exopolysaccharides, virulence factors, or cell wall synthesis or they start an internal program of biofilm dispersal. Some of their targets are more conserved among pathogens than the receptors for quorum sensing autoinducers mediating quorum-sensing, enabling a broader application of the drug. The broad spectrum of mechanisms, the diversity of bioactive compounds, their activity against several targets, and the conservation of some targets among bacterial pathogens are promising aspects for several clinical applications of this type of biofilm-controlling compound in the future.

A personal history of research on microbial biofilms and biofilm infections

The observation of aggregated microorganisms surrounded by a self-produced matrix adhering to surfaces or located in tissues or secretions is as old as microbiology, with both Leeuwenhoek and Pasteur describing the phenomenon. In environmental and technical microbiology, biofilms were already shown 80-90 years ago to be important for biofouling on submerged surfaces, e.g. ships. The concept of biofilm infections and their importance in medicine is, however, < 40 years old and was started by Jendresen's observations of acquired dental pellicles and my own observations of heaps of Pseudomonas aeruginosa cells in sputum and lung tissue from chronically infected cystic fibrosis patients. The term biofilm was introduced into medicine in 1985 by Costerton. In the following decades, it became obvious that biofilm infections are widespread in medicine, and their importance is now generally accepted.