Polymicrobial wound infections: pathophysiology and current therapeutic approaches

Silver-pig skin nanocomposites and mesenchymal stem cells: suitable antibiofilm cellular dressings for wound healing

Background

Treatment of severe or chronic skin wounds is an important challenge facing medicine and a significant health care burden. Proper wound healing is often affected by bacterial infection; where biofilm formation is one of the main risks and particularly problematic because it confers protection to microorganisms against antibiotics. One avenue to prevent bacterial colonization of wounds is the use of silver nanoparticles (AgNPs); which have proved to be effective against non-multidrug-resistant and multidrug-resistant bacteria. In addition, the use of mesenchymal stem cells (MSC) is an excellent option to improve wound healing due to their capability for differentiation and release of relevant growth factors. Finally, radiosterilized pig skin (RPS) is a biomatrix successfully used as wound dressing to avoid massive water loss, which represents an excellent carrier to deliver MSC into wound beds. Together, AgNPs, RPS and MSC represent a potential dressing to control massive water loss, prevent bacterial infection and enhance skin regeneration; three essential processes for appropriate wound healing with minimum scaring.

Results

We synthesized stable 10 nm-diameter spherical AgNPs that showed 21- and 16-fold increase in bacteria growth inhibition (in comparison to antibiotics) against clinical strains Staphylococcus aureus and Stenotrophomonas maltophilia, respectively. RPS samples were impregnated with different AgNPs suspensions to develop RPS-AgNPs nanocomposites with different AgNPs concentrations. Nanocomposites showed inhibition zones, in Kirby–Bauer assay, against both clinical bacteria tested. Nanocomposites also displayed antibiofilm properties against S. aureus and S. maltophilia from RPS samples impregnated with 250 and 1000 ppm AgNPs suspensions, respectively. MSC were isolated from adipose tissue and seeded on nanocomposites; cells survived on nanocomposites impregnated with up to 250 ppm AgNPs suspensions, showing 35% reduction in cell viability, in comparison to cells on RPS. Cells on nanocomposites proliferated with culture days, although the number of MSC on nanocomposites at 24 h of culture was lower than that on RPS.

Conclusions

AgNPs with better bactericide activity than antibiotics were synthesized. RPS-AgNPs nanocomposites impregnated with 125 and 250 ppm AgNPs suspensions decreased bacterial growth, decreased biofilm formation and were permissive for survival and proliferation of MSC; constituting promising multi-functional dressings for successful treatment of skin wounds.

Electronic supplementary material

The online version of this article (10.1186/s12951-017-0331-0) contains supplementary material, which is available to authorized users.

Synthesized zinc peroxide nanoparticles (ZnO2-NPs): a novel antimicrobial, anti-elastase, anti-keratinase, and anti-inflammatory approach toward polymicrobial burn wounds

Increasing of multidrug resistance (MDR) remains an intractable challenge for burn patients. Innovative nanomaterials are also in high demand for the development of new antimicrobial biomaterials that inevitably have opened new therapeutic horizons in medical approaches and lead to many efforts for synthesizing new metal oxide nanoparticles (NPs) for better control of the MDR associated with the polymicrobial burn wounds. Recently, it seems that metal oxides can truly be considered as highly efficient inorganic agents with antimicrobial properties. In this study, zinc peroxide NPs (ZnO₂-NPs) were synthesized using the co-precipitation method. Synthesized ZnO₂-NPs were characterized by X-ray diffraction, Fourier transformed infrared, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and ultraviolet-visible spectroscopy. The characterization techniques revealed synthesis of the pure phase of non-agglomerated ZnO₂-NPs having sizes in the range of 15–25 nm with a transition temperature of 211°C. Antimicrobial activity of ZnO₂-NPs was determined against MDR Pseudomonas aeruginosa (PA) and Aspergillus niger (AN) strains isolated from burn wound infections. Both strains, PA6 and AN4, were found to be more susceptible strains to ZnO₂-NPs. In addition, a significant decrease in elastase and keratinase activities was recorded with increased concentrations of ZnO₂-NPs until 200 µg/mL. ZnO₂-NPs revealed a significant anti-inflammatory activity against PA6 and AN4 strains as demonstrated by membrane stabilization, albumin denaturation, and proteinase inhibition. Moreover, the results of in vivo histopathology assessment confirmed the potential role of ZnO₂-NPs in the improvement of skin wound healing in the experimental animal models. Clearly, the synthesized ZnO₂-NPs have demonstrated a competitive capability as antimicrobial, anti-elastase, anti-keratinase, and anti-inflammatory candidates, suggesting that the ZnO₂-NPs are promising metal oxides that are potentially valued for biomedical applications.

Candida-Bacteria Interactions: Their Impact on Human Disease

Candida species are the most common infectious fungal species in humans; out of the approximately 150 known species, Candida albicans is the leading pathogenic species, largely affecting immunocompromised individuals. Apart from its role as the primary etiology for various types of candidiasis, C. albicans is known to contribute to polymicrobial infections. Polymicrobial interactions, particularly between C. albicans and bacterial species, have gained recent interest in which polymicrobial biofilm virulence mechanisms have been studied including adhesion, invasion, quorum sensing, and development of antimicrobial resistance. These trans-kingdom interactions, either synergistic or antagonistic, may help modulate the virulence and pathogenicity of both Candida and bacteria while uniquely impacting the pathogen-host immune response. As antibiotic and antifungal resistance increases, there is a great need to explore the intermicrobial cross-talk with a focus on the treatment of Candida-associated polymicrobial infections. This article explores the current literature on the interactions between Candida and clinically important bacteria and evaluates these interactions in the context of pathogenesis, diagnosis, and disease management.

Application of Hyperosmotic Nanoemulsions in Wound Healing: Partial Thickness Injury Model in Swine

Objective: In this work, we introduce a novel hyperosmotic nanoemulsion (HNE) topical agent for use in wound healing. These topical emulsion complexes combine a lipophilic thymol nanoemulsion with a hyperosmotic saccharide matrix. This combination has been previously shown to possess synergistic antimicrobial activity against a host of common and drug-resistant pathogens in vitro. Approach: In this study, we present additional data to assess the safety and efficacy of these emulsions in a partial thickness injury model in swine. Ten wounds sized 2 × 3.5 cm were created in 18 pigs using an electrodermatome set at a depth of 0.76 mm. The wounds were subsequently contaminated with a cocktail of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans at 5 × 10⁷ total colony forming unit per wound. Treatments were subdivided in the control group and emulsion concentrations at 0.0%, 0.01%, 0.03%, and 0.063% thymol content. Longitudinal metrics for wound healing included rate of reepithelialization, wound bed color measurements, amount of wound exudate, wound swab culture data, and histological examination at 4, 7, and 14 days. The cosmetics of the healed wound were obtained at day 14 with three-dimensional photogrammetry. Results: Experimental results showed that HNE reduced the wound level bacteria count by ∼0.5-1 log versus controls after 24 h. The amount of pathogen reduction was weakly correlated to the concentration of the emulsion. In addition, all HNE groups maintained a moist wound environment and showed increased fibrin formation and improved hemostatic response. Innovation: No significant difference in the rate of reepithelialization or wound closure was found between treatment concentrations and control groups. HNE treatment did not demonstrate any adverse host tissue response. Conclusion: These results suggest HNE may be a candidate for reducing wound bacterial counts without compromising reepithelialization.

Shaping of cutaneous function by encounters with commensals

The skin is the largest organ in the human body and provides the first line of defence against environmental attack and pathogen invasion. It harbor multiple commensal microbial communities at different body sites, which play important roles in sensing the environment, protecting against colonization and infection of pathogens, and guiding the host immune system in response to foreign invasions. The skin microbiome is largely variable between individuals and body sites, with several core commensal members commonly shared among individuals at the healthy state. These microbial commensals are essential to skin health and can potentially lead to disease when their abundances and activities change due to alterations in the environment or in the host. While recent advances in sequencing technologies have enabled a large number of studies to characterize the taxonomic composition of the skin microbiome at various body sites and under different physiological conditions, we have limited understanding of the microbiome composition and dynamics at the strain level, which is highly important to many microbe-related diseases. Functional studies of the skin microbial communities and the interactions among community members and with the host are currently scant, warranting future investigations. In this review, we summarize the recent findings on the skin microbiome, highlighting the roles of the major commensals, including bacteria, fungi and bacteriophages, in modulating skin functions in health and disease. Functional studies of the skin microbiota at the metatranscriptomic and proteomic levels are also included to illustrate the interactions between the microbiota and the host skin.

The microbiological signature of human cutaneous leishmaniasis lesions exhibits restricted bacterial diversity compared to healthy skin

Localised cutaneous leishmaniasis (LCL) is the most common form of cutaneous leishmaniasis characterised by single or multiple painless chronic ulcers, which commonly presents with secondary bacterial infection. Previous culture-based studies have found staphylococci, streptococci, and opportunistic pathogenic bacteria in LCL lesions, but there have been no comparisons to normal skin. In addition, this approach has strong bias for determining bacterial composition. The present study tested the hypothesis that bacterial communities in LCL lesions differ from those found on healthy skin (HS). Using a high throughput amplicon sequencing approach, which allows for better populational evaluation due to greater depth coverage and the Quantitative Insights Into Microbial Ecology pipeline, we compared the microbiological signature of LCL lesions with that of contralateral HS from the same individuals.Streptococcus, Staphylococcus,Fusobacterium and other strict or facultative anaerobic bacteria composed the LCL microbiome. Aerobic and facultative anaerobic bacteria found in HS, including environmental bacteria, were significantly decreased in LCL lesions (p < 0.01). This paper presents the first comprehensive microbiome identification from LCL lesions with next generation sequence methodology and shows a marked reduction of bacterial diversity in the lesions.

Chronic Wound Biofilms: Pathogenesis and Potential Therapies

Chronic wounds are a growing medical problem that cause high rates of morbidity and mortality, costing the healthcare industry in the United States millions of dollars annually. Chronic wound healing is hampered by the presence of bacterial infections that form biofilms, in which the bacteria are encased in exopolysaccharide (EPS) and are less metabolically active than their free-living counterparts. Bacterial biofilms make chronic wounds more refractory to treatment and slow tissue repair by stimulating chronic inflammation at the wound site. Bacterial species communicate through a mechanism known as quorum sensing (QS) to regulate and coordinate the gene expression that is important for virulence-factor production, including biofilm formation. This review focuses on the relationships between chronic wounds, biofilms, and QS in the virulence of chronic-wound pathogens.

Auxotrophic Actinobacillus pleurpneumoniae grows in multispecies biofilms without the need for nicotinamide-adenine dinucleotide (NAD) supplementation

Background

Actinobacillus pleuropneumoniae is the etiologic agent of porcine contagious pleuropneumonia, which causes important worldwide economic losses in the swine industry. Several respiratory tract infections are associated with biofilm formation, and A. pleuropneumoniae has the ability to form biofilms in vitro. Biofilms are structured communities of bacterial cells enclosed in a self-produced polymer matrix that are attached to an abiotic or biotic surface. Virtually all bacteria can grow as a biofilm, and multi-species biofilms are the most common form of microbial growth in nature. The goal of this study was to determine the ability of A. pleuropneumoniae to form multi-species biofilms with other bacteria frequently founded in pig farms, in the absence of pyridine compounds (nicotinamide mononucleotide [NMN], nicotinamide riboside [NR] or nicotinamide adenine dinucleotide [NAD]) that are essential for the growth of A. pleuropneumoniae.

Results

For the biofilm assay, strain 719, a field isolate of A. pleuropneumoniae serovar 1, was mixed with swine isolates of Streptococcus suis, Bordetella bronchiseptica, Pasteurella multocida, Staphylococcus aureus or Escherichia coli, and deposited in 96-well microtiter plates. Based on the CFU results, A. pleuropneumoniae was able to grow with every species tested in the absence of pyridine compounds in the culture media. Interestingly, A. pleuropneumoniae was also able to form strong biofilms when mixed with S. suis, B. bronchiseptica or S. aureus. In the presence of E. coli, A. pleuropneumoniae only formed a weak biofilm. The live and dead populations, and the matrix composition of multi-species biofilms were also characterized using fluorescent markers and enzyme treatments. The results indicated that poly-N-acetyl-glucosamine remains the primary component responsible for the biofilm structure.

Conclusions

In conclusion, A. pleuropneumoniae apparently is able to satisfy the requirement of pyridine compounds through of other swine pathogens by cross-feeding, which enables A. pleuropneumoniae to grow and form multi-species biofilms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0742-3) contains supplementary material, which is available to authorized users.

Do Polymicrobial Intra-Abdominal Infections Have Worse Outcomes than Monomicrobial Intra-Abdominal Infections?

BACKGROUND

Numerous studies have demonstrated microorganism interaction through signaling molecules, some of which are recognized by other bacterial species. This interspecies synergy can prove detrimental to the human host in polymicrobial infections. We hypothesized that polymicrobial intra-abdominal infections (IAI) have worse outcomes than monomicrobial infections.

METHODS

Data from the Study to Optimize Peritoneal Infection Therapy (STOP-IT), a prospective, multicenter, randomized controlled trial, were reviewed for all occurrences of IAI having culture results available. Patients in STOP-IT had been randomized to receive four days of antibiotics vs. antibiotics until two days after clinical symptom resolution. Patients with polymicrobial and monomicrobial infections were compared by univariable analysis using the Wilcoxon rank sum, χ(2), and Fisher exact tests.

RESULTS

Culture results were available for 336 of 518 patients (65%). The durations of antibiotic therapy in polymicrobial (n = 225) and monomicrobial IAI (n = 111) were equal (p = 0.78). Univariable analysis demonstrated similar demographics in the two populations. The 37 patients (11%) with inflammatory bowel disease were more likely to have polymicrobial IAI (p = 0.05). Polymicrobial infections were not associated with a higher risk of surgical site infection, recurrent IAI, or death.

CONCLUSION

Contrary to our hypothesis, polymicrobial IAI do not have worse outcomes than monomicrobial infections. These results suggest polymicrobial IAI can be treated the same as monomicrobial IAI.

Inhibition of filamentous fungi by ketoconazole-functionalized electrospun nanofibers

Nanotechnology strategies have been used for delivery and controlled release of antimicrobial drugs. Electrospun nanofibers can be versatile vehicles to incorporate antimicrobials. In this work, poly-ε-caprolactone nanofibers functionalized with ketoconazole were produced by electrospinning and tested against filamentous fungi. Ketoconazole-free nanofibers were produced as controls. Functionalized nanofibers showed antifungal activity against Aspergillus flavus, A. carbonarius, A. niger, Aspergillus sp. A29, Fusarium oxysporum and Penicillium citrinum by agar diffusion test. Inhibitory zones ranging from 6 to 44mm were observed, this larger inhibition was against A. flavus. The nanofibers were incubated in different simulant solutions to evaluate the ketoconazole release, which was only detected in the solution containing 5% (v/v) Tween 20. Electron microscopy images showed the nanofibers with ketoconazole presented mean diameters of 526nm, and the degradation of the nanofiber structures could be observed by electron microscopy after incubation in simulant solution. Infrared and thermal analyses indicated that ketoconazole was dispersed without chemical interactions with the polycaprolactone matrix. These results suggest that polycaprolactone nanofibers incorporating ketoconazole may be an interesting alternative to control pathogenic fungi.

Infected animal models for tissue engineering

Infection is one of the most common complications associated with medical interventions and implants. As tissue engineering strategies to replace missing or damaged tissue advance, the focus on prevention and treatment of concomitant infection has also begun to emerge as an important area of research. Because the in vivo environment is a complex interaction between host tissue, implanted materials, and native immune system that cannot be replicated in vitro, animal models of infection are integral in evaluating the safety and efficacy of experimental treatments for infection. In this review, considerations for selecting an animal model, established models of infection, and areas that require further model development are discussed with regard to cutaneous, fascial, and orthopedic infections.

Metal-Based Antibacterial Substrates for Biomedical Applications

The interest in nanotechnology and the growing concern for the antibiotic resistance demonstrated by many microorganisms have recently stimulated many efforts in designing innovative biomaterials and substrates with antibacterial properties. Among the implemented strategies to control the incidence of infections associated with the use of biomedical device and implants, interesting routes are represented by the incorporation of bactericidal agents onto the surface of biomaterials for the prevention of bacterial adhesion and biofilm growth. Natural products and particularly bioactive metals such as silver, copper and zinc represent an interesting alternative for the development of advanced biomaterials with antimicrobial properties. This review presents an overview of recent progress in the modification of biomaterials as well as the most attractive techniques for the deposition of antimicrobial coatings on different substrates for biomedical application. Moreover, some research activities and results achieved by the authors in the development of antibacterial materials are also presented and discussed.

Atmospheric pressure nonthermal plasmas for bacterial biofilm prevention and eradication

Biofilms are three-dimensional structures formed by surface-attached microorganisms and their extracellular products. Biofilms formed by pathogenic microorganisms play an important role in human diseases. Higher resistance to antimicrobial agents and changes in microbial physiology make treating biofilm infections very complex. Atmospheric pressure nonthermal plasmas (NTPs) are a novel and powerful tool for antimicrobial treatment. The microbicidal activity of NTPs has an unspecific character due to the synergetic actions of bioactive components of the plasma torch, including charged particles, reactive species, and UV radiation. This review focuses on specific traits of biofilms, their role in human diseases, and those effects of NTP that are helpful for treating biofilm infections. The authors discuss NTP-based strategies for biofilm control, such as surface modifications to prevent bacterial adhesion, killing bacteria in biofilms, and biofilm destruction with NTPs. The unspecific character of microbicidal activity, proven polymer modification and destruction abilities, low toxicity for human tissues and absence of long-living toxic compounds make NTPs a very promising tool for biofilm prevention and control.

Carmellose Mucoadhesive Oral Films Containing Vermiculite/Chlorhexidine Nanocomposites as Innovative Biomaterials for Treatment of Oral Infections

Infectious stomatitis represents the most common oral cavity ailments. Current therapy is insufficiently effective because of the short residence time of topical liquid or semisolid medical formulations. An innovative application form based on bioadhesive polymers featuring prolonged residence time on the oral mucosa may be a solution to this challenge. This formulation consists of a mucoadhesive oral film with incorporated nanocomposite biomaterial that is able to release the drug directly at the target area. This study describes the unique approach of preparing mucoadhesive oral films from carmellose with incorporating a nanotechnologically modified clay mineral intercalated with chlorhexidine. The multivariate data analysis was employed to evaluate the influence of the formulation and process variables on the properties of the medical preparation. This evaluation was complemented by testing the antimicrobial and antimycotic activity of prepared films with the aim of finding the most suitable composition for clinical application. Generally, the best results were obtained with sample containing 20 mg of chlorhexidine diacetate carried by vermiculite, with carmellose in the form of nonwoven textile in its structure. In addition to its promising physicomechanical, chemical, and mucoadhesive properties, the formulation inhibited the growth of Staphylococcus and Candida; the effect was prolonged for tens of hours.

Approach to chronic wound infections

Infection is the likeliest single cause of delayed healing in healing of chronic open wounds by secondary intention. If neglected it can progress from contamination to colonization and local infection through to systemic infection, sepsis and multiple organ dysfunction syndrome, and it can be life-threatening. Infection in chronic wounds is not as easy to define as in acute wounds, and is complicated by the presence of biofilms. There is, as yet, no diagnostic for biofilm presence, but it contributes to excessive inflammation - through excessive and prolonged stimulation of nitric oxide, inflammatory cytokines and free radicals - and activation of immune complexes and complement, leading to a delay in healing. Control of biofilm is a key part of chronic wound management. Maintenance debridement and use of topical antimicrobials (antiseptics) are more effective than antibiotics, which should be reserved for treating spreading local and systemic infection. The continuing rise of antimicrobial resistance to antibiotics should lead us to reserve their use for these indications, as no new effective antibiotics are in the research pipeline. Antiseptics are effective through many mechanisms of action, unlike antibiotics, which makes the development of resistance to them unlikely. There is little evidence to support the theoretical risk that antiseptics select resistant pathogens. However, the use of antiseptic dressings for preventing and managing biofilm and infection progression needs further research involving well-designed, randomized controlled trials.

Characterization of local delivery with amphotericin B and vancomycin from modified chitosan sponges and functional biofilm prevention evaluation

Polymicrobial musculoskeletal wound infections are troublesome complications and can be difficult to treat when caused by invasive fungi or bacteria. However, few local antifungal delivery systems have been studied. Chitosan and polyethylene glycol (PEG) sponge local antifungal delivery systems have been developed for adjunctive therapy to reduce musculoskeletal wound contamination. This study evaluated the effects of blending PEG, at 6,000 or 8,000 g/mol, with chitosan in sponge form on in vitro amphotericin B and vancomycin elution, eluate activity, cytocompatibility, and in vivo prevention of a bacterial biofilm. Blended chitosan sponges released both amphotericin B and vancomycin in vitro. All tested amphotericin B eluates remained active against Candida albicans, and vancomycin eluates from blended sponges maintained activity against Staphylococcus aureus. Amphotericin B eluates obtained after 1 h from blended sponges elicited 62-95% losses in fibroblast viability, but 3 h eluates only caused 22-60% decreases in viability. In a Staphylococcus aureus infected mouse catheter biofilm prevention model, vancomycin loaded chitosan/PEG 6000 sponge cleared bacteria from 100% of the catheters, with reduced clearance rate observed in other sponges. These results indicate that the chitosan/PEG blended sponges have potential for local antifungal and/or antibiotic combination delivery as an adjunctive therapy to prevent wound infections.