The High Impact of Staphylococcus aureus Biofilm Culture Medium on In Vitro Outcomes of Antimicrobial Activity of Wound Antiseptics and Antibiotic

Preparation and Biological Activity of Lignin-Silver Hybrid Nanoparticles

Silver nanoparticles (AgNPs) are excellent antimicrobial agents and promising candidates for preventing or treating bacterial infections caused by antibiotic resistant strains. However, their increasing use in commercial products raises concerns about their environmental impact. In addition, traditional physicochemical approaches often involve harmful agents and excessive energy consumption, resulting in AgNPs with short-term colloidal stability and silver ion leaching. To address these issues, we designed stable hybrid lignin-silver nanoparticles (AgLigNPs) intended to effectively hit bacterial envelopes as a main antimicrobial target. The lignin nanoparticles (LigNPs), serving as a reducing and stabilizing agent for AgNPs, have a median size of 256 nm and a circularity of 0.985. These LigNPs were prepared using the dialysis solvent exchange method, producing spherical particles stable under alkaline conditions and featuring reducing groups oriented toward a wrinkled surface, facilitating AgNPs synthesis and attachment. Maximum accumulation of silver on the LigNP surface was observed at a mass reaction ratio mAg:mLig of 0.25, at pH 11. The AgLigNPs completely inhibited suspension growth and reduced biofilm development by 50% in three tested strains of Pseudomonas aeruginosa at a concentration of 80/9.5 (lignin/silver) mg L-1. Compared to unattached AgNPs, AgLigNPs required two to eight times lower silver concentrations to achieve complete inhibition. Additionally, our silver-containing nanosystems were effective against bacteria at safe concentrations in HEK-293 and HaCaT tissue cultures. Stability experiments revealed that the nanosystems tend to aggregate in media used for bacterial cell cultures but remain stable in media used for tissue cultures. In all tested media, the nanoparticles retained their integrity, and the presence of lignin facilitated the prevention of silver ions from leaching. Overall, our data demonstrate the suitability of AgLigNPs for further valorization in the biomedical sector.

The chronic wound milieu changes essential oils' antibiofilm activity-an in vitro and larval model study

Essential Oils (EOs) are currently being researched as potential antibiofilm agents to combat infections related to chronic wound biofilms. As documented in the literature, EOs' in vitro antibacterial properties are often assessed using standard microbiological media and conditions that do not accurately reflect the actual environment of a chronic wound. To address this issue, In vitro Wound Milieu (IVWM) medium, which closely resembles the environment of a chronic wound, was applied for culturing S. aureus biofilms (n = 12) in this research. Biofilms cultivated in the standard Tryptic Soy Broth (TSB) medium served as a control for the experiment. Key biofilm features were analyzed and compared. Subsequently, staphylococci were exposed to the activity of thyme or rosemary EOs (T-EO and R-EO, respectively). As proof of concept, the cytotoxicity of T-EO and its antimicrobial in vivo activity were assessed using a G. mellonella larvae model. Key features of biofilm-forming cells were lower in the IVWM than in the TSB medium: biomass (up to 8 times), metabolic activity (up to 9 times), cell number (up to 100 times), and the live/dead cells ratio. Conversely, biofilm thickness was higher (up to 25%) in IVWM. These differences translated into varied responses of the biofilms to EOs exposure. The application of T-EO led to a greater reduction (up to 2 times) in 67% of biofilm-forming strains in IVWM compared to the TSB medium. Conversely, exposure to R-EO resulted in a higher reduction (up to 2.6 times) of 83% of biofilm-forming strains in TSB than in IVWM. The application of T-EO was not only non-toxic to G. mellonella larvae but also increased the survival of larvae infected with staphylococci (from 48 to 85%). Our findings suggest that EOs not only show promise as agents for treating biofilm-related wound infections but also that providing conditions reflecting the specific niche of the human body is of paramount importance in influencing the results obtained. However, before clinical application, challenges related to the methods of assessing their activity, microbial intra-species variability, and different levels of activity of various EOs should be analyzed and standardized.

Chitosan-Based Dressing as a Sustained Delivery System for Bioactive Cytokines

Wounds represent a common occurrence in human life. Consequently, scientific investigations are underway to advance wound healing methodologies, with a notable focus on dressings imbued with biologically active compounds capable of orchestrating the wound microenvironment through meticulously regulated release mechanisms. Among these bioactive agents are cytokines, which, when administered to the wound milieu without appropriate protection, undergo rapid loss of their functional attributes. Within the context of this research, we present a method for fabricating dressings enriched with G-CSF (granulocyte colony-stimulating factor) or GM-CSF (granulocyte-macrophage colony-stimulating factor), showcasing both biological activity and protracted release dynamics. Based on Ligasano, a commercial polyurethane foam dressing, and chitosan crosslinked with TPP (sodium tripolyphosphate), these dressings are noncytotoxic and enable cytokine incorporation. The recovery of cytokines from dressings varied based on the dressing preparation and storage techniques (without modification, drying, freeze-drying followed by storage at 4 °C or freeze-drying followed by storage at 24 °C) and cytokine type. Generally, drying reduced cytokine levels and their bioactivity, especially with G-CSF. The recovery of G-CSF from unmodified dressings was lower compared to GM-CSF (60% vs. 80%). In summary, our freeze-drying approach enables the storage of G-CSF or GM-CSF enriched dressings at 24 °C with minimal cytokine loss, preserving their biological activity and thus enhancing future clinical availability.

Culture Shock: An Investigation into the Tolerance of Pathogenic Biofilms to Antiseptics in Environments Resembling the Chronic Wound Milieu

Credible assessment methods must be applied to evaluate antiseptics' in vitro activity reliably. Studies indicate that the medium for biofilm culturing should resemble the conditions present at the site of infection. We cultured S. aureus, S. epidermidis, P. aeruginosa, C. albicans, and E. coli biofilms in IVWM (In Vitro Wound Milieu)-the medium reflecting wound milieu-and were compared to the ones cultured in the laboratory microbiological Mueller-Hinton (MH) medium. We analyzed and compared crucial biofilm characteristics and treated microbes with polyhexamethylene biguanide hydrochloride (PHMB), povidone-iodine (PVP-I), and super-oxidized solution with hypochlorites (SOHs). Biofilm biomass of S. aureus and S. epidermidis was higher in IVWM than in MH medium. Microbes cultured in IVWM exhibited greater metabolic activity and thickness than in MH medium. Biofilm of the majority of microbial species was more resistant to PHMB and PVP-I in the IVWM than in the MH medium. P. aeruginosa displayed a two-fold lower MBEC value of PHMB in the IVWM than in the MH medium. PHMB was more effective in the IVWM than in the MH medium against S. aureus biofilm cultured on a biocellulose carrier (instead of polystyrene). The applied improvement of the standard in vitro methodology allows us to predict the effects of treatment of non-healing wounds with specific antiseptics.

Biodiversity of Skin Microbiota as an Important Biomarker for Wound Healing

Cutaneous wound healing is a natural and complex repair process that is implicated within four stages. However, microorganisms (e.g., bacteria) can easily penetrate through the skin tissue from the wound bed, which may lead to disbalance in the skin microbiota. Although commensal and pathogenic bacteria are in equilibrium in normal skin, their imbalance in the wound area can cause the delay or impairment of cutaneous wounds. Moreover, skin microbiota is in constant crosstalk with the immune system and epithelial cells, which has significance for the healing of a wound. Therefore, understanding the major bacteria species in the cutaneous wound as well as their communication with the immune system has gained prominence in a way that allows for the emergence of a new perspective for wound healing. In this review, the major bacteria isolated from skin wounds, the role of the crosstalk between the cutaneous microbiome and immune system to heal wounds, the identification techniques of these bacteria populations, and the applied therapies to manipulate the skin microbiota are investigated.

Effectiveness of a polyhexamethylene biguanide-containing wound cleansing solution using experimental biofilm models

OBJECTIVE

Antiseptics are widely used in wound management to prevent or treat wound infections, and have been shown to have antibiofilm efficacy. The objective of this study was to assess the effectiveness of a polyhexamethylene biguanide (PHMB)-containing wound cleansing and irrigation solution on model biofilm of pathogens known to cause wound infections compared with a number of other antimicrobial wound cleansing and irrigation solutions.

METHOD

Staphylococcus aureus and Pseudomonas aeruginosa single-species biofilms were cultured using microtitre plate and Centers for Disease Control and Prevention (CDC) biofilm reactor methods. Following a 24-hour incubation period, the biofilms were rinsed to remove planktonic microorganisms and then challenged with wound cleansing and irrigation solutions. Following incubation of the biofilms with a variety of concentrations of the test solutions (50%, 75% or 100%) for 20, 30, 40, 50 or 60 minutes, remaining viable organisms from the treated biofilms were quantified.

RESULTS

The six antimicrobial wound cleansing and irrigation solutions used were all effective in eradicating Staphylococcus aureus biofilm bacteria in both test models. However, the results were more variable for the more tolerant Pseudomonas aeruginosa biofilm. Only one of the six solutions (sea salt and oxychlorite/NaOCl-containing solution) was able to eradicate Pseudomonas aeruginosa biofilm using the microtitre plate assay. Of the six solutions, three (a solution containing PHMB and poloxamer 188 surfactant, a solution containing hypochlorous acid (HOCl) and a solution containing NaOCl/HOCl) showed increasing levels of eradication of Pseudomonas aeruginosa biofilm microorganisms with increasing concentration and exposure time. Using the CDC biofilm reactor model, all six cleansing and irrigation solutions, except for the solution containing HOCl, were able to eradicate Pseudomonas aeruginosa biofilms such that no viable microorganisms were recovered.

CONCLUSION

This study demonstrated that a PHMB-containing wound cleansing and irrigation solution was as effective as other antimicrobial wound irrigation solutions for antibiofilm efficacy. Together with the low toxicity, good safety profile and absence of any reported acquisition of bacterial resistance to PHMB, the antibiofilm effectiveness data support the alignment of this cleansing and irrigation solution with antimicrobial stewardship (AMS) strategies.

Comparison of antibiofilm activity of low-concentrated hypochlorites vs polyhexanide-containing antiseptic

Chronic wound infection is highly associated with morbidity and endangers the patient's life. Therefore, wound care products must have a potent antimicrobial and biofilm-eradicating effect. In this work, the antimicrobial/antibiofilm activity of two low-concentrated chlorine-based and releasing solutions was investigated on a total of 78 strains of methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans, using the cohesive spectrum of in vitro settings, including microtiter plate models, biofilm-oriented antiseptic test, cellulose-based biofilm model, biofilm bioreactors and Bioflux model. The antiseptic containing polyhexamethylene biguanide was used in the character of usability control of performed tests. The results obtained by static biofilm models indicate that low-concentrated chlorine-based and releasing solutions display none to moderate antibiofilm activity, while data obtained by means of the Bioflux model, providing flow conditions, indicate the moderate antibiofilm activity of substances compared with the polyhexanide antiseptic. Considering in vitro data presented in this manuscript, the earlier reported favorable clinical results of low-concentrated hypochlorites should be considered rather an effect of their rinsing activity combined with low cytotoxicity but not the antimicrobial effect per se. For the treatment of heavily biofilm-infected wounds, polyhexanide should be considered the agent of choice because of its higher efficacy against pathogenic biofilms.

Polyhexamethylene biguanide and its antimicrobial role in wound healing: a narrative review

A wound offers an ideal environment for the growth and proliferation of a variety of microorganisms which, in some cases, may lead to localised or even systemic infections that can be catastrophic for the patient; the development of biofilms exacerbates these infections. Over the past few decades, there has been a progressive development of antimicrobial resistance (AMR) in microorganisms across the board in healthcare sectors. Such resistant microorganisms have arisen primarily due to the misuse and overuse of antimicrobial treatments, and the subsequent ability of microorganisms to rapidly change and mutate as a defence mechanism against treatment (e.g., antibiotics). These resistant microorganisms are now at such a level that they are of grave concern to the World Health Organization (WHO), and are one of the leading causes of illness and mortality in the 21st century. Treatment of such infections becomes imperative but presents a significant challenge for the clinician in that treatment must be effective but not add to the development of new microbes with AMR. The strategy of antimicrobial stewardship (AMS) has stemmed from the need to counteract these resistant microorganisms and requires that current antimicrobial treatments be used wisely to prevent amplification of AMR. It also requires new, improved or alternative methods of treatment that will not worsen the situation. Thus, any antimicrobial treatment should be effective while not causing further development of resistance. Some antiseptics fall into this category and, in particular, polyhexamethylene hydrochloride biguanide (PHMB) has certain characteristics that make it an ideal solution to this problem of AMR, specifically within wound care applications. PHMB is a broad-spectrum antimicrobial that kills bacteria, fungi, parasites and certain viruses with a high therapeutic index, and is widely used in clinics, homes and industry. It has been used for many years and has not been shown to cause development of resistance; it is safe (non-cytotoxic), not causing damage to newly growing wound tissue. Importantly there is substantial evidence for its effective use in wound care applications, providing a sound basis for evidence-based practice. This review presents the evidence for the use of PHMB treatments in wound care and its alignment with AMS for the prevention and treatment of wound infection.

The Assessment of Activity of Antiseptic Agents against Biofilm of Staphylococcus aureus Measured with the Use of Processed Microscopic Images

Staphylococcal biofilms are major causative factors of non-healing wound infections. Their treatment algorithms recommend the use of locally applied antiseptic agents to counteract the spread of infection. The efficacy of antiseptics against biofilm is assessed in vitro by a set of standard quantitative and semi-quantitative methods. The development of software for image processing additionally allowed for the obtainment of quantitative data from microscopic images of biofilm dyed with propidium iodine and SYTO-9 reagents, differentiating dead cells from live ones. In this work, the method of assessment of the impact of antiseptic agents on staphylococcal biofilm in vitro, based on biofilms’ processed images, was proposed and scrutinized with regard to clinically relevant antiseptics, polyhexanide, povidone–iodine and hypochlorite. The standard quantitative culturing method was applied to validate the obtained data from processed images. The results indicated significantly higher activity of polyhexanide and povidone–iodine than hypochlorite against staphylococcal biofilm. Taking into account the fact that in vitro results of the efficacy of antiseptic agents against staphylococcal biofilm are frequently applied to back up their use in hospitals and ambulatory units, our work should be considered an important tool; providing reliable, quantitative data in this regard.

The Medium Composition Impacts Staphylococcus aureus Biofilm Formation and Susceptibility to Antibiotics Applied in the Treatment of Bone Infections

The biofilm-associated infections of bones are life-threatening diseases, requiring application of dedicated antibiotics in order to counteract the tissue damage and spread of microorganisms. The in vitro analyses on biofilm formation and susceptibility to antibiotics are frequently carried out using methods that do not reflect conditions at the site of infection. To evaluate the influence of nutrient accessibility on Staphylococcus aureus biofilm development in vitro, a cohesive set of analyses in three different compositional media was performed. Next, the efficacy of four antibiotics used in bone infection treatment, including gentamycin, ciprofloxacin, levofloxacin, and vancomycin, against staphylococcal biofilm, was also assessed. The results show a significant reduction in the ability of biofilm to grow in a medium containing elements occurring in the serum, which also translated into the diversified changes in the efficacy of used antibiotics, compared to the setting in which conventional media were applied. The differences indicate the need for implementation of adequate in vitro models that closely mimic the infection site. The results of the present research may be considered an essential step toward the development of in vitro analyses aiming to accurately indicate the most suitable antibiotic to be applied against biofilm-related infections of bones.

The cross-linked bacterial cellulose impregnated with octenidine dihydrochloride-based antiseptic as an antibacterial dressing material for highly-exuding, infected wounds

The highly absorbent, antibacterial dressings with a sustained release of the antimicrobial are considered necessary measures to counteract chronic wound biofilm-based infections. This study aimed to analyze wet and dry bacterial cellulose (BC) materials, modified by chemical cross-linking, and impregnated with an antiseptic based on octenidine dihydrochloride (OCT) in the context of its antibiofilm/antibacterial activity, exudate absorption, and cytotoxicity. The native BC was obtained from cost-effective, ecological-friendly potato juice (leftover from the starch industry). The ability to absorb and retain OCT, exudate absorption capacity, the kinetics of OCT release as well as antibiofilm/antibacterial activity of modified BC materials against biofilm-forming and planktonic bacteria (Staphylococcus aureus and Pseudomonas aeruginosa) were investigated. The performed analyses revealed that modified BC materials, thanks to their layered structure with numerous air spaces, were characterized by sustained exudate absorption and OCT release profile, which allowed them to exhibit high antimicrobial activity for up to 7 days, with a reduction of planktonic and biofilm cells of 84-100% and 69-93%, respectively. The modified BC materials showed also no cytotoxicity against fibroblast cell line L929 in vitro and were characterized by firm adhesion to the curved surfaces. These results indicate that cross-linked BC impregnated with OCT may be a particularly promising dressing material (obtained using sustainable processes), especially in the treatment of biofilm-infected, highly-exuding wounds.

The effects of rotating magnetic field and antiseptic on in vitro pathogenic biofilm and its milieu

The application of various magnetic fields for boosting the efficacy of different antimicrobial molecules or in the character of a self-reliant antimicrobial agent is considered a promising approach to eradicating bacterial biofilm-related infections. The purpose of this study was to analyze the phenomenon of increased activity of octenidine dihydrochloride-based antiseptic (OCT) against Staphylococcus aureus and Pseudomonas aeruginosa biofilms in the presence of the rotating magnetic field (RMF) of two frequencies, 5 and 50 Hz, in the in vitro model consisting of stacked agar discs, placed in increasing distance from the source of the antiseptic solution. The biofilm-forming cells' viability and morphology as well as biofilm matrix structure and composition were analyzed. Also, octenidine dihydrochloride permeability through biofilm and porous agar obstacles was determined for the RMF-exposed versus unexposed settings. The exposure to RMF or OCT apart did not lead to biofilm destruction, contrary to the setting in which these two agents were used together. The performed analyses revealed the effect of RMF not only on biofilms (weakening of cell wall/membranes, disturbed morphology of cells, altered biofilm matrix porosity, and composition) but also on its milieu (altered penetrability of octenidine dihydrochloride through biofilm/agar obstacles). Our results suggest that the combination of RMF and OCT can be particularly promising in eradicating biofilms located in such areas as wound pockets, where physical obstacles limit antiseptic activity.

The In Vitro Ability of Klebsiella pneumoniae to Form Biofilm and the Potential of Various Compounds to Eradicate It from Urinary Catheters

Urinary infections related to the presence of bacterial biofilm on catheters are responsible for loss of patients’ health and, due to their high frequency of occurrence, generate a significant economic burden for hospitals. Klebsiella pneumoniae is a pathogen frequently isolated from this type of infection. In this study, using a cohesive set of techniques performed under stationary and flow conditions, we assessed the ability of 120 K. pneumoniae strains to form biofilm on various surfaces, including catheters, and evaluated the usefulness of clinically applied and experimental compounds to remove biofilm. The results of our study indicate the high impact of intraspecies variability with respect to K. pneumoniae biofilm formation and its susceptibility to antimicrobials and revealed the crucial role of mechanical flushing out of the biofilm from the catheter’s surface with use of locally active antimicrobials. Therefore, our work, although of in vitro character, may be considered an important step in the direction of efficient reduction of K. pneumoniae biofilm-related hospital infections associated with the presence of urine catheters.