Efficacy of NVC-422 against Staphylococcus aureus biofilms in a sheep biofilm model of sinusitis

Pathophysiology and management of Staphylococcus aureus in nasal polyp disease

INTRODUCTION

Staphylococcus aureus (S. aureus) is a common pathogen that frequently colonizes the sinonasal cavity. Recent studies demonstrated the essential role of Staphylococcus aureus in the pathophysiology of uncontrolled severe chronic rhinosinusitis with nasal polyps (NP) by initiating an immune response to the germ and its products, resulting in type 2 inflammation.

AREAS COVERED

This review aims to summarize the evidence for the role of S. aureus in the development of NP disease including S. aureus-related virulence factors, the pathophysiologic mechanisms used by S. aureus, and the synergistic effects of S. aureus and other pathogens. It also describes the current management of S. aureus associated with NPs as well as potential therapeutic strategies that are used in clinical practice.

EXPERT OPINION

S. aureus is able to damage the nasal mucosal epithelial barrier, impair the clearance of the host immune system, and trigger adaptive and innate immune reactions which lead to the formation of inflammation and nasal polyp growth. Further studies should focus on the development of novel therapeutic strategies, such as biologics, bacteriophages, probiotics, and nanomedicine, which could be used to treat S. aureus and its immunological consequences in the future.

Novel strategies for inhibition of bacterial biofilm in chronic rhinosinusitis

An important role has been recently reported for bacterial biofilm in the pathophysiology of chronic diseases, such as chronic rhinosinusitis (CRS). CRS, affecting sinonasal mucosa, is a persistent inflammatory condition with a high prevalence around the world. Although the exact pathological mechanism of this disease has not been elicited yet, biofilm formation is known to lead to a more significant symptom burden and major objective clinical indicators. The high prevalence of multidrug-resistant bacteria has severely restricted the application of antibiotics in recent years. Furthermore, systemic antibiotic therapy, on top of its insufficient concentration to eradicate bacteria in the sinonasal biofilm, often causes toxicity, antibiotic resistance, and an effect on the natural microbiota, in patients. Thus, coming up with alternative therapeutic options instead of systemic antibiotic therapy is emphasized in the treatment of bacterial biofilm in CRS patients. The use of topical antibiotic therapy and antibiotic eluting sinus stents that induce higher antibiotic concentration, and decrease side effects could be helpful. Besides, recent research recognized that various natural products, nitric oxide, and bacteriophage therapy, in addition to the hindered biofilm formation, could degrade the established bacterial biofilm. However, despite these improvements, new antibacterial agents and CRS biofilm interactions are complicated and need extensive research. Finally, most studies were performed in vitro, and more preclinical animal models and human studies are required to confirm the collected data. The present review is specifically discussing potential therapeutic strategies for the treatment of bacterial biofilm in CRS patients.

Safety and efficacy of a bacteriophage cocktail in an in vivo model of Pseudomonas aeruginosa sinusitis

Pseudomonas aeruginosa (PA) is a bacterial pathogen that frequently displays antibiotic resistance. Its presence within the sinuses of chronic rhinosinusitis sufferers is associated with poorer quality of life. Obligately lytic bacteriophages (phages) are viruses that infect, replicate within, and lyse bacteria, causing bacterial death. The aims of this study were to assess the safety and efficacy of a PA phage cocktail (CT-PA) in a sheep model of rhinosinusitis. The sheep rhinosinusitis model was adapted to simulate PA infection in sheep frontal sinuses. To assess efficacy, after a 7-day biofilm formation period, sheep received twice-daily frontal trephine flushes of CT-PA or saline for 1 week. Biofilm quantitation on frontal sinus mucosa was performed using LIVE/DEAD BacLight staining. To assess safety, sheep received twice-daily frontal trephine flushes of CT-PA or vehicle control for 3 weeks. Blood and fecal samples were collected throughout treatment. Histopathology of frontal sinus, lung, heart, liver, spleen, and kidney tissue was performed. Sinus cilia were visualized using scanning electron microscopy (SEM). The Efficacy arm showed a statistically significant reduction in biofilm biomass with all concentrations of CT-PA tested (P < 0.05). Phage presence in sinuses was maintained for at least 16hours after the final flush. All Safety arm sheep completed 3 weeks of treatment. Phage was detected consistently in feces and sporadically in blood and organ samples. Histology and SEM of tissues revealed no treatment-related damage. In conclusion, CT-PA was able to decrease sinus PA biofilm at concentrations of 10⁸-10¹⁰ PFU/mL. No safety concerns were noted.

Safety and Efficacy of Topical Chitogel- Deferiprone-Gallium Protoporphyrin in Sheep Model

Objectives: Increasing antimicrobial resistance has presented new challenges to the treatment of recalcitrant chronic rhinosinusitis fuelling a continuous search for novel antibiofilm agents. This study aimed to assess the safety and efficacy of Chitogel (Chitogel®, Wellington New Zealand) combined with novel antibiofilm agents Deferiprone and Gallium Protoporphyrin (CG-DG) as a topical treatment against S. aureus biofilms in vivo.

Methods: To assess safety, 8 sheep were divided into two groups of 7 day treatments (n = 8 sinuses per treatment); (1) Chitogel (CG) with twice daily saline flush, and (2) CG-DG gel with twice daily saline flush. Tissue morphology was analyzed using histology and scanning electron microscopy (SEM). To assess efficacy we used a S. aureus sheep sinusitis model. Fifteen sheep were divided into three groups of 7 day treatments (n = 10 sinuses per treatment); (1) twice daily saline flush (NT), (2) Chitogel (CG) with twice daily saline flush, and (3) CG-DG gel with twice daily saline flush. Biofilm biomass across all groups was compared using LIVE/DEAD BacLight stain and confocal scanning laser microscopy.

Results: Safety study showed no cilia denudation on scanning electron microscopy and no change in sinus mucosa histopathology when comparing CG-DG to CG treated sheep. COMSTAT2 assessment of biofilm biomass showed a significant reduction in CG-DG treated sheep compared to NT controls.

Conclusion: Results indicate that CG-DG is safe and effective against S. aureus biofilms in a sheep sinusitis model and could represent a viable treatment option in the clinical setting.

Efficacy of silk fibroin-nano silver against Staphylococcus aureus biofilms in a rabbit model of sinusitis

BACKGROUND

Staphylococcus aureus biofilms contribute significantly to the recalcitrant nature of chronic rhinosinusitis. In previous studies, it has been shown that silk fibroin-nano silver solution can eliminate S. aureus biofilms in vitro, which suggests a potential role of this novel agent in the treatment of biofilm-associated diseases, such as sinusitis.

OBJECTIVE

The aim of this study was to investigate the efficacy of silk fibroin-nano silver solution as a topical anti-biofilm agent in a rabbit model of sinusitis.

METHODS

Biofilm-associated sinusitis models were established in 24 New Zealand White rabbits by gelatin sponge placement and S. aureus inoculation through a hole drilled into the anterolateral wall of the right maxillary sinus. After 4 weeks, indwelling catheters were placed into the maxillary sinus. Different concentrations of silk fibroin-nano silver solution or normal saline were irrigated slowly into the maxillary sinus via the indwelling catheters. After 7 days of irrigation, the rabbits were sacrificed. The sinus mucosa was harvested and examined for biofilm biomass as well as morphological integrity of the epithelium by scanning electron microscopy.

RESULTS

Silk fibroin-nano silver solution was found to be most effective in reducing the biomass of the S. aureus biofilms at a concentration of 384 mg/L, followed by the concentration of 153.6 mg/L, when compared with saline. After treatment with 384 mg/L silk fibroin-nano silver solution, the biofilms were completely eliminated and the injured epithelium was almost restored with regenerated cilia on the surface.

CONCLUSION

Silk fibroin-nano silver solution was found to be an effective topical agent against S. aureus biofilms in the rabbit model of sinusitis, and its effect was concentration-dependent.

Biofilm and Osteitis in Refractory Chronic Rhinosinusitis

Our understanding of chronic rhinosinusitis (CRS) show biofilm and osteitis play a role in the disease's pathogenesis and refractory. Studies point to its role in pathogenesis and poor prognosis. Outside the research laboratory, biofilm detection remains difficult and specific treatment remains elusive. It is believed that osteitis is a nidus of inflammation and occurs more commonly in patients with refractory CRS. However, osteitis may be exacerbated by surgery and a marker of refractory disease, not a causative agent. Surgery remains the mainstay treatment for biofilm and osteitis with mechanical disruption and removal of disease load providing the most effective treatment.

Biofilms in chronic rhinosinusitis: Pathophysiology and therapeutic strategies

BACKGROUND

There is increasing evidence that biofilms are critical to the pathophysiology of chronic infections including chronic rhinosinusitis (CRS). Until relatively recently, our understanding of biofilms was limited. Recent advances in methods for biofilm identification and molecular biology have offered new insights into the role of biofilms in CRS. With these insights, investigators have begun to investigate novel therapeutic strategies that may disrupt or eradicate biofilms in CRS.

OBJECTIVE

This review seeks to explore the evidence implicating biofilms in CRS, discuss potential anti-biofilm therapeutic strategies, and suggest future directions for research.

RESULTS

The existing evidence strongly supports the role of biofilms in the pathogenesis of CRS. Several anti-biofilm therapies have been investigated for use in CRS and these are at variable stages of development. Generally, these strategies: 1) neutralize biofilm microbes; 2) disperse existing biofilms; or 3) disrupt quorum sensing. Several of the most promising anti-biofilm therapeutic strategies are reviewed.

CONCLUSIONS

A better understanding of biofilm function and their contribution to the CRS disease process will be pivotal to the development of novel treatments that may augment and, potentially, redefine the CRS treatment paradigm. There is tremendous potential for future research.

Animal Models in CRS and Pathophysiologic Insights Gained: A Systematic Review

OBJECTIVE

Chronic rhinosinusitis (CRS) is a multifactorial inflammatory disease. In particular, CRS with eosinophilic features and/or nasal polyps (NPs) is often recalcitrant to current treatment; thus, appropriate animal models are mandatory to elucidate the pathogenesis of CRS and develop novel and efficient treatment modalities. The author reviewed the recently proposed animal models in CRS and discussed the pathophysiologic insights gained. Data Sources: Articles in the English language referenced in MEDLINE/PubMed from the year 2006 onward (for last 10 years). Review Methods: Review of the literature regarding animal models and related pathologic insights in CRS.

RESULTS

Mouse, rabbit, and sheep models of CRS have been used for studying the pathogenesis of CRS. Most of researchers adopted animal models of CRS to prove any molecular mechanisms or therapeutic efficacy. In vitro or human findings and related hypothesis were evaluated in vivo using these models. In addition, novel therapeutic candidates for CRS with or without NP have been applied to animal models.

CONCLUSION

Animal models have elicited insights into the pathogenesis of CRS and also have been useful in testing new treatment modalities. Although there are still clear limitations in the animal studies, newly proposed or revised animal models would be helpful to understand the exact pathophysiology of CRS.

Role of biofilm in children with recurrent upper respiratory tract infections

Recurrent respiratory tract infections (RRTIs) are very common in children and a major challenge for pediatricians. In the last few years, bacterial biofilms have been linked to RRTIs and antibiotic resistance, and have raised serious concerns regarding the therapeutic management of recurrent middle ear diseases, chronic rhinosinusitis, and recurrent pharyngotonsillitis. This paper aims to review the new insights into biofilm-related upper respiratory tract infections in children and possible therapeutic strategies. It focuses on the clinical implications for recurrent disease and on studies in pediatric patients. Analysis of the literature showed that the involvement of bacterial biofilm in recurrent upper airway tract infections is an emerging problem that may lead to serious concerns about infection control. Despite the large amount of research within this field, detailed insight into the complex structure of bacterial biofilms and the ultrastructural and biochemical mechanisms responsible for its evasion of the immune system and resistance to treatments is currently lacking. In the future, additional emphasis should be placed on biofilm management as a component of therapeutic strategies. This goal can be attained by finding feasible methods for detecting biofilms in vivo and identifying effective methods for administering treatments that eradicate preexisting bacterial biofilms or hinder bacterial adhesion to respiratory cells.

When and how should we treat biofilms in chronic sinusitis?

PURPOSE OF REVIEW

Biofilms have been observed on the sinus mucosa of patients with chronic rhinosinusitis and are associated with poor clinical outcomes after surgery. This article summarizes the recent studies which describe the efficacy of treating biofilms in chronic rhinosinusitis.

RECENT FINDINGS

Biofilms are polymicrobial communities comprised of bacteria that tend to be more antibiotic-resistant than when in planktonic forms. Antibiotic therapy against biofilms is usually associated with relapse following cessation of treatment and may also have an adverse effect on normal commensal microflora. Surfactants can improve clinical symptoms, but their use has been limited by side effects. Other treatment modalities that physically remove or disrupt biofilms, such as ultrasound, have shown some efficacy in small trials. The impact of surgery on biofilms has not been extensively investigated.

SUMMARY

The nature of biofilms makes their removal difficult. No currently available treatment directed against them has demonstrated lasting efficacy.

Bactericidal activity of N-chlorotaurine against biofilm-forming bacteria grown on metal disks

Many orthopedic surgeons consider surgical irrigation and debridement with prosthesis retention as a treatment option for postoperative infections. Usually, saline solution with no added antimicrobial agent is used for irrigation. We investigated the activity of N-chlorotaurine (NCT) against various biofilm-forming bacteria in vitro and thereby gained significant information on its usability as a soluble and well-tolerated active chlorine compound in orthopedic surgery. Biofilms of Staphylococcus aureus were grown on metal alloy disks and in polystyrene dishes for 48 h. Subsequently, they were incubated for 15 min to 7 h in buffered solutions containing therapeutically applicable concentrations of NCT (1%, 0.5%, and 0.1%; 5.5 to 55 mM) at 37°C. NCT inactivated the biofilm in a time- and dose-dependent manner. Scanning electron microscopy revealed disturbance of the biofilm architecture by rupture of the extracellular matrix. Assays with reduction of carboxanilide (XTT) showed inhibition of the metabolism of the bacteria in biofilms. Quantitative cultures confirmed killing of S. aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa biofilms on metal alloy disks by NCT. Clinical isolates were slightly more resistant than ATCC type strains, but counts of CFU were reduced at least 10-fold by 1% NCT within 15 min in all cases. NCT showed microbicidal activity against various bacterial strains in biofilms. Whether this can be transferred to the clinical situation should be the aim of future studies.

Bacteriophage Reduces Biofilm of Staphylococcus Aureus Ex Vivo Isolates from Chronic Rhinosinusitis Patients

Background

Staphylococcus aureus is the most common organism in recalcitrant chronic rhinosinusitis (CRS) and is often resistant to traditional antibiotic therapy. Bacteriophages (“phages”) are a potential candidate for a new, effective therapy. For phages to be useful in setting CRS, two minimum requirements must be presented: (1) phages must be effective against S. aureus biofilms and (2) phages must have a broad spectrum of activity. This study aimed to assess the in vitro activity of a phage cocktail (CockTail of Staphylococcus aureus specific bacteriophage [CT-SA]) against S. aureus biofilms and a broad panel of strains isolated from patients with CRS.

Methods

The study examined 66 clinical isolates (CIs) of S. aureus. All isolates were tested for the susceptibility to phage lysis by spotting CT-SA onto bacterial lawns. To measure its effect on S. aureus biofilms, a minimum biofilm eradication concentration assay was used, using five S. aureus isolates. Biofilms of these isolates were grown, treated with CT-SA for 48 hours, fluorescently stained, and viewed using confocal scanning laser microscopy.

Results

CT-SA lysed 62 of 66 (94%) CIs of S. aureus. CT-SA treatment yielded significant reductions in biofilm mass for 4/5 CIs tested and for ATCC 25923. Challenge of S. aureus with a single phage resulted in the emergence of bacteriophage-insensitive mutants (BIM) with a frequency of 10−7, and challenge with CT-SA completely prevented their development.

Conclusion

This study indicates that phage cocktail CT-SA can effectively eliminate S. aureus, in planktonic and biofilm forms, from the great majority of CIs from this hospital setting. In addition, its potential effect in preventing the emergence BIMs was a established. Thus, CT-SA has the potential to treat S. aureus infection and biofilm in CRS patients.

N-chloramines, a promising class of well-tolerated topical anti-infectives

Antibiotic resistance is a growing public health crisis. To address the development of bacterial resistance, the use of antibiotics has to be minimized for nonsystemic applications in humans, as well as in animals and plants. Possible substitutes with low potential for developing resistance are active chlorine compounds that have been in clinical use for over 180 years. These agents are characterized by pronounced differences in their chlorinating and/or oxidizing activity, with hypochlorous acid (HOCl) as the strongest and organic chloramines as the weakest members. Bacterial killing in clinical practice is often associated with unwanted side effects such as chlorine consumption, tissue irritation, and pain, increasing proportionally with the chlorinating/oxidizing potency. Since the chloramines are able to effectively kill pathogens (bacteria, fungi, viruses, protozoa), their application as anti-infectives is advisable, all the more so as they exhibit additional beneficial properties such as destruction of toxins, degradation of biofilms, and anticoagulative and anti-inflammatory activities. Within the ample field of chloramines, the stable N-chloro derivatives of β-aminosulfonic acids are most therapeutically advanced. Being available as sodium salts, they distinguish themselves by good solubility and absence of smell. Important representatives are N-chlorotaurine, a natural compound occurring in the human immune system, and novel mono- and dichloro derivatives of dimethyltaurine, which feature improved stability.