Polymicrobial Biofilm Organization of Staphylococcus aureus and Pseudomonas aeruginosa in a Chronic Wound Environment

Understanding and treating diabetic foot ulcers: Insights into the role of cutaneous microbiota and innovative therapies

Background

Notoriously known as the silent pandemic, chronic, non-healing diabetic foot ulcers (DFUs), pose a significant rate of incidence for amputation and are a major cause of morbidity. Alarmingly, the treatment and management strategies of chronic wounds represent a significant economic and health burden as well as a momentous drain on resources with billions per annum being spent in the US and UK alone. Defective wound healing is a major pathophysiological condition which propagates an acute wound to a chronic wound, further propelled by underlying conditions such as diabetes and vascular complications which are more prevalent amongst the elderly. Chronic wounds are prone to infection, which can exacerbate the condition, occasionally resulting in amputation for the patient, despite the intervention of modern therapies. However, amputation can only yield a 5-year survival rate for 50% of patients, highlighting the need for new treatments for chronic wounds.

Findings

The dynamic cutaneous microbiota is comprised of diverse microorganisms that often aid wound healing. Conversely, the chronic wound microbiome consists of a combination of common skin commensals such as Staphylococcus aureus and Staphylococcus epidermidis, as well as the opportunistic pathogen Pseudomonas aeruginosa. These bacteria have been identified as the most prevalent bacterial pathogens isolated from chronic wounds and contribute to prolific biofilm formation decreasing the efficiency of antimicrobials and further perpetuating a hyper-inflammatory state.

Discussion and Conclusion

Here, we review recent advances and provide a new perspective on alternative treatments including phage and microbiome transplant therapies and how the definitive role of the cutaneous microbiota impacts the aetiology of DFUs.

Sanitization of hydroponic farming facilities in Singapore: what, why, and how

This study performed microbial analysis of nutrient film technique (NFT) hydroponic systems on three indoor farms in Singapore (the "what"). To justify the necessity of sanitizing hydroponic systems, strong biofilm-forming bacteria were isolated from the facility and investigated for their influence on Salmonella colonization on polyvinyl chloride (PVC) coupons in hydroponic nutrient solutions (the "why"). Finally, sanitization solutions were evaluated with both laboratory-scale and field-scale tests (the "how"). As a result, the microbiome composition in NFT systems was found to be highly farm specific. The strong biofilm formers Corynebacterium tuberculostearicum C2 and Pseudoxanthomonas mexicana C3 were found to facilitate the attachment and colonization of Salmonella on PVC coupons. When forming dual-species biofilms, the presence of C2 and C3 also significantly promoted the growth of Salmonella (P < 0.05). Compared with hydrogen peroxide (H2O2) and sodium percarbonate (SPC), sodium hypochlorite (NaOCl) exhibited superior efficacy in biofilm removal. At 50 ppm, NaOCl reduced the Salmonella Typhimurium, C2, and C3 counts to <1 log CFU/cm2 within 12 h, whereas neither 3% H2O2 nor 1% SPC achieved this effect. In operational hydroponic systems, the concentration of NaOCl needed to achieve biofilm elimination increased to 500 ppm, likely due to the presence of organic matter accumulated during crop cultivation and the greater persistence of naturally formed multispecies biofilms. Sanitization using 500 ppm NaOCl for 12 h did not impede subsequent plant growth, but chlorination byproduct chlorate was detected at high levels in the hydroponic solution and in plants in the sanitized systems without rinsing.

IMPORTANCE

This study's significance lies first in its elucidation of the necessity of sanitizing hydroponic farming systems. The microbiome in hydroponic systems, although mostly nonpathogenic, might serve as a hotbed for pathogen colonization and thus pose a risk for food safety. We thus explored sanitization solutions with both laboratory-scale and field-scale tests. Of the three tested sanitizers, NaOCl was the most effective and economical option, whereas one must note the vital importance of rinsing the hydroponic systems after sanitization with NaOCl.

Sodium alginate-based nanofibers loaded with Capparis Sepiaria plant extract for wound healing

Burn wounds are associated with infections, drug resistance, allergic reactions, odour, bleeding, excess exudates, and scars, requiring prolonged hospital stay. It is crucial to develop wound dressings that can effectively combat allergic reactions and drug resistance, inhibit infections, and absorb excess exudates to accelerate wound healing. To overcome the above-mentioned problems associated with burn wounds, SA/PVA/PLGA/Capparis sepiaria and SA/PVA/Capparis sepiaria nanofibers incorporated with Capparis sepiaria plant extract were prepared using an electrospinning technique. Fourier-transform infrared spectroscopy confirmed the successful incorporation of the extract into the nanofibers without any interaction between the extract and the polymers. The nanofibers displayed porous morphology and a rough surface suitable for cellular adhesion and proliferation. SA/PVA/PLGA/Capparis sepiaria and SA/PVA/Capparis sepiaria nanofibers demonstrated significant antibacterial effects against wound infection-associated bacterial strains: Pseudomonas aeruginosa, Enterococcus faecalis, Mycobaterium smegmatis, Escherichia coli, Enterobacter cloacae, Proteus vulgaris, and Staphylococcus aureus. Cytocompatibility studies using HaCaT cells revealed the non-toxicity of the nanofibers. SA/PVA/PLGA/Capparis sepiaria and SA/PVA/Capparis sepiaria nanofibers exhibited hemostatic properties, resulting from the synergistic effect of the plant extract and polymers. The in vitro scratch wound healing assay showed that the SA/PVA/Capparis sepiaria nanofiber wound-healing capability is more than the plant extract and a commercially available wound dressing. The wound-healing potential of SA/PVA/Capparis sepiaria nanofiber is attributed to the synergistic effect of the phytochemicals present in the extract, their porosity, and the ECM-mimicking structure of the nanofibers. The findings suggest that the electrospun nanofibers loaded with Capparis sepiaria extract are promising wound dressings that should be explored for burn wounds.

Staphylococcus aureus biofilm: Formulation, regulatory, and emerging natural products-derived therapeutics

Staphylococcus aureus can readily form biofilm which enhances the drug-resistance, resulting in life-threatening infections involving different organs. Biofilm formation occurs due to a series of developmental events including bacterial adhesion, aggregation, biofilm maturation, and dispersion, which are controlled by multiple regulatory systems. Rapidly increasing research and development outcomes on natural products targeting S. aureus biofilm formation and/or regulation led to an emergent application of active phytochemicals and combinations. This review aimed at providing an in-depth understanding of biofilm formation and regulation mechanisms for S. aureus, outlining the most important antibiofilm strategies and potential targets of natural products, and summarizing the latest progress in combating S. aureus biofilm with plant-derived natural products. These findings provided further evidence for novel antibiofilm drugs research and clinical therapies.

A review of chemical signaling mechanisms underlying quorum sensing and its inhibition in Staphylococcus aureus

Staphylococcus aureus is a significant bacterium responsible for multiple infections and is a primary cause of fatalities among patients in hospital environments. The advent of pathogenic bacteria such as methicillin-resistant S. aureus revealed the shortcomings of employing antibiotics to treat bacterial infectious diseases. Quorum sensing enhances S. aureus's survivability through signaling processes. Targeting the key components of quorum sensing has drawn much interest nowadays as a promising strategy for combating infections caused by bacteria. Concentrating on the accessory gene regulator quorum-sensing mechanism is the most commonly suggested anti-virulence approach for S.aureus. Quorum quenching is a common strategy for controlling illnesses triggered by microorganisms since it reduces the pathogenicity of bacteria and improves bacterial biofilm susceptibility to antibiotics, thus providing an intriguing prospect for drug discovery. Quorum sensing inhibition reduces selective stresses and constrains the emergence of antibiotic resistance while limiting bacterial pathogenicity. This review examines the quorum sensing mechanisms involved in S. aureus, quorum sensing targets and gene regulation, environmental factors affecting quorum sensing, quorum sensing inhibition, natural products as quorum sensing inhibitory agents and novel therapeutical strategies to target quorum sensing in S. aureus as drug developing technique to augment conventional antibiotic approaches.

Multifunctional antibacterial hydrogels for chronic wound management

Chronic wounds have gradually evolved into a global health challenge, comprising long-term non-healing wounds, local tissue necrosis, and even amputation in severe cases. Accordingly, chronic wounds place a considerable psychological and economic burden on patients and society. Chronic wounds have multifaceted pathogenesis involving excessive inflammation, insufficient angiogenesis, and elevated reactive oxygen species levels, with bacterial infection playing a crucial role. Hydrogels, renowned for their excellent biocompatibility, moisture retention, swelling properties, and oxygen permeability, have emerged as promising wound repair dressings. However, hydrogels with singular functions fall short of addressing the complex requirements associated with chronic wound healing. Hence, current research emphasises the development of multifunctional antibacterial hydrogels. This article reviews chronic wound characteristics and the properties and classification of antibacterial hydrogels, as well as their potential application in chronic wound management.

Extracellular vesicles from Staphylococcus aureus promote the pathogenicity of Pseudomonas aeruginosa

Co-infections with Staphylococcus aureus and Pseudomonas aeruginosa are common in patients with chronic wounds, but little is known about their synergistic effect mediated by extracellular vesicles (EVs). In this study, we investigated the effect of EVs derived from S. aureus (SaEVs) on the pathogenicity of P. aeruginosa. By using lipophilic dye, we could confirm the fusion between SaEV and P. aeruginosa membranes. However, SaEVs did not alter the growth and antibiotic susceptible pattern of P. aeruginosa. Differential proteomic analysis between SaEV-treated and non-treated P. aeruginosa was performed, and the results revealed that lipopolysaccharide (LPS) biosynthesis protein in P. aeruginosa significantly increased after SaEV-treatment. Regarding this result, we also found that SaEVs promoted LPS production, biofilm formation, and expression of polysaccharide polymerization-related genes in P. aeruginosa. Furthermore, invasion of epithelial cells by SaEV-pretreated P. aeruginosa was enhanced. On the other hand, uptake of P. aeruginosa by RAW 264.7 macrophages was impaired after pretreatment P. aeruginosa with SaEVs. Proteomic analysis SaEVs revealed that SaEVs contain the proteins involving in host cell colonization, inhibition of host immune response, anti-phagocytosis of the macrophages, and protein translocation and iron uptake of S. aureus. In conclusion, SaEVs serve as a mediator that promote P. aeruginosa pathogenicity by enhancing LPS biosynthesis, biofilm formation, epithelial cell invasion, and macrophage uptake impairment.

The Staphylococcus aureus ArlS Kinase Inhibitor Tilmicosin Has Potent Anti-Biofilm Activity in Both Static and Flow Conditions

Staphylococcus aureus can form biofilms on biotic surfaces or implanted materials, leading to biofilm-associated diseases in humans and animals that are refractory to conventional antibiotic treatment. Recent studies indicate that the unique ArlRS regulatory system in S. aureus is a promising target for screening inhibitors that may eradicate formed biofilms, retard virulence and break antimicrobial resistance. In this study, by screening in the library of FDA-approved drugs, tilmicosin was found to inhibit ArlS histidine kinase activity (IC50 = 1.09 μM). By constructing a promoter-fluorescence reporter system, we found that tilmicosin at a concentration of 0.75 μM or 1.5 μM displayed strong inhibition on the expression of the ArlRS regulon genes spx and mgrA in the S. aureus USA300 strain. Microplate assay and confocal laser scanning microscopy showed that tilmicosin at a sub-minimal inhibitory concentration (MIC) had a potent inhibitory effect on biofilms formed by multiple S. aureus strains and a strong biofilm-forming strain of S. epidermidis. In addition, tilmicosin at three-fold of MIC disrupted USA300 mature biofilms and had a strong bactericidal effect on embedded bacteria. Furthermore, in a BioFlux flow biofilm assay, tilmicosin showed potent anti-biofilm activity and synergized with oxacillin against USA300.

Solving polymicrobial puzzles: evolutionary dynamics and future directions

Polymicrobial infections include various microorganisms, often necessitating different treatment methods than a monomicrobial infection. Scientists have been puzzled by the complex interactions within these communities for generations. The presence of specific microorganisms warrants a chronic infection and impacts crucial factors such as virulence and antibiotic susceptibility. Game theory is valuable for scenarios involving multiple decision-makers, but its relevance to polymicrobial infections is limited. Eco-evolutionary dynamics introduce causation for multiple proteomic interactions like metabolic syntropy and niche segregation. The review culminates both these giants to form evolutionary dynamics (ED). There is a significant amount of literature on inter-bacterial interactions that remain unsynchronised. Such raw data can only be moulded by analysing the ED involved. The review culminates the inter-bacterial interactions in multiple clinically relevant polymicrobial infections like chronic wounds, CAUTI, otitis media and dental carries. The data is further moulded with ED to analyse the niche colonisation of two notoriously competitive bacteria: S.aureus and P.aeruginosa. The review attempts to develop a future trajectory for polymicrobial research by following recent innovative strategies incorporating ED to curb polymicrobial infections.

Differential Susceptibility of Mixed Polymicrobial Biofilms Involving Ocular Coccoid Bacteria (Staphylococcus aureus and S. epidermidis) and a Filamentous Fungus (Fusarium solani) on Ex Vivo Human Corneas

Biofilms confer several advantages to the organisms associated with them, such as increased resistances to antibacterial and antifungal compounds compared to free living cells. Compared to monomicrobial biofilms involving a single microorganism, biofilms composed of microorganisms affiliated to bacterial and fungal kingdoms are predominant in nature. Despite the predominance of polymicrobial biofilms, and more so mixed polymicrobial biofilms, they are rarely studied. The objective of the current study is to evaluate the potential of ocular bacteria and a filamentous fungus to form monomicrobial and mixed polymicrobial biofilms on synthetic and natural substrates and to monitor their response to antibiotics. In this sense, we demonstrated that the ocular pathogens Staphylococcus aureus, S. epidermidis, and Fusarium solani form monomicrobial and mixed polymicrobial biofilms both on tissue culture polystyrene plates and on ex vivo human corneas from cadavers using confocal microscopy and scanning electron microscopy. Additionally, the mixed polymicrobial biofilms involving the above ocular bacteria and a filamentous fungus were less susceptible to different antibacterials and antifungals in relation to the corresponding control planktonic cells. Further, the MICs to the screened antibacterials and antifungals in polymicrobial biofilms involving a bacterium or a fungus was either increased, decreased, or unchanged compared to the corresponding individual bacterial or fungal biofilm. The results would be useful to the ophthalmologist to plan effective treatment regimens for the eye since these are common pathogens of the eye causing keratitis, endophthalmitis, conjunctivitis, etc.

Do Anti-Biofilm Antibiotics Have a Place in the Treatment of Diabetic Foot Osteomyelitis?

The choice of antibiotic regimens for use in patients presenting with diabetic foot osteomyelitis and their duration differs according to the situation. Antibiotics play a more important role in the medical option where no infected bone has been resected, while their role is reduced but not negligible in the case of surgical options. Some studies have reported the presence of biofilm structures in bone samples taken from patients with diabetic foot osteomyelitis, which raises the question of the place of anti-biofilm antibiotic regimens in this setting. During the last two decades, clinical studies have suggested a potential benefit for anti-biofilm antibiotics, mainly rifampicin against staphylococci and fluoroquinolones against gram-negative bacilli. However, no data from randomized controlled studies have been reported so far. The present work provides a summary of the available data on the question of the place of anti-biofilm antibiotics for the treatment of diabetic foot osteomyelitis, but also the potential limitations of such treatments.