Effect of Poly(Vinyl Pyrrolidone) on Iodine Release from Acrylate-Endcapped Urethane-Based Poly(Ethylene Glycol) Hydrogels as Antibacterial Wound Dressing.

Infections are still a major cause of morbidity in burn wounds. Although silver has been used strongly in past centuries as an anti-bacterial, it can lead to allergic reactions, bacterial resistance, and delayed wound healing. Iodine-based antibacterials are becoming an interesting alternative. In this work, the effect of complexation with poly(vinyl pyrrolidone) (PVP) and poly(ethylene oxide) (PEO)-based polymers is explored by using different acrylate-endcapped urethane-based poly(ethylene glycol) (AUP) polymers, varying the molar mass (MM) of the poly(ethylene glycol) (PEG) backbone, with possible addition of PVP. The higher MM AUP outperforms the swelling potential of commercial wound dressings such as Kaltostat, Aquacel Ag, and Hydrosorb and all MM show superior mechanical properties. The addition of iodine to the polymers is compared to Iso-Betadine Tulle (IBT). Interestingly, the addition of PVP does not lead to increased iodine complexation compared to the blank AUP polymers, while all have a prolonged iodine release compared to the IBT, which leads to a burst release. The observed prolonged release also leads to larger inhibition zones during antibacterial tests. Complexing iodine in AUP polymers with or without PVP leads to antimicrobial wound dressings which may hold potential for future application to treat infected wounds.

Pooling isolates to address the diversity in antimicrobial susceptibility of Pseudomonas aeruginosa in cystic fibrosis.

IMPORTANCE: People with cystic fibrosis (pwCF) often suffer from chronic lung infections with Pseudomonas aeruginosa. While antibiotics are still commonly used to treat P. aeruginosa infections, there is a high discordance between in vitro and in vivo antibiotic efficacy, which contributes to suboptimal antibiotic therapy. In the present study, we found that isolates from the same sputum sample had highly diverse antibiotic resistance profiles [based on the minimal inhibitory concentration (MIC)], which may explain the reported discrepancy between in vitro and in vivo antibiotic efficacy. Through systematic analysis, we report that pooling nine isolates per sputum sample significantly decreased intrasample diversity in MIC and influenced clinical interpretation of antibiotic susceptibility tests compared to single isolate testing. Hence, pooling of isolates may offer a solution to obtain a consistent MIC test result and could lead to optimizing antibiotic therapy in pwCF and other infectious diseases where diversity in antibiotic resistance is observed.

Antibiofilm Activities of Borneol-Citral-Loaded Pickering Emulsions against Pseudomonas aeruginosa and Staphylococcus aureus in Physiologically Relevant Chronic Infection Models.

Phytochemicals are promising antibacterials for the development of novel antibiofilm drugs, but their antibiofilm activity in physiologically relevant model systems is poorly characterized. As the host microenvironment can interfere with the activity of the phytochemicals, mimicking the complex environment found in biofilm associated infections is essential to predict the clinical potential of novel phytochemical-based antimicrobials. In the present study, we examined the antibiofilm activity of borneol, citral, and combinations of both as well as their Pickering emulsions against Staphylococcus aureus and Pseudomonas aeruginosa in an in vivo-like synthetic cystic fibrosis medium (SCFM2) model, an in vitro wound model (consisting of an artificial dermis and blood components at physiological levels), and an in vivo Galleria mellonella model. The Pickering emulsions demonstrated an enhanced biofilm inhibitory activity compared to both citral and the borneol/citral combination, reducing the minimum biofilm inhibitory concentration (MBIC) values up to 2 to 4 times against P. aeruginosa PAO1 and 2 to 8 times against S. aureus P8-AE1 in SCMF2. In addition, citral, the combination borneol/citral, and their Pickering emulsions can completely eliminate the established biofilm of S. aureus P8-AE1. The effectiveness of Pickering emulsions was also demonstrated in the wound model with a reduction of up to 4.8 log units in biofilm formation by S. aureus Mu50. Furthermore, citral and Pickering emulsions exhibited a significant degree of protection against S. aureus infection in the G. mellonella model. The present findings reveal the potential of citral- or borneol/citral-based Pickering emulsions as a type of alternative antibiofilm candidate to control pathogenicity in chronic infection. IMPORTANCE There is clearly an urgent need for novel formulations with antimicrobial and antibiofilm activity, but while there are plenty of studies investigating them using simple in vitro systems, there is a lack of studies in which (combinations of) phytochemicals are evaluated in relevant models that closely resemble the in vivo situation. Here, we examined the antibiofilm activity of borneol, citral, and their combination as well as Pickering emulsions (stabilized by solid particles) of these compounds. Activity was tested against Staphylococcus aureus and Pseudomonas aeruginosa in in vitro models mimicking cystic fibrosis sputum and wounds as well as in an in vivo Galleria mellonella model. The Pickering emulsions showed drastically increased antibiofilm activity compared to that of the compounds as such in both in vitro models and protected G. mellonella larvae from S. aureus-induced killing. Our data show that Pickering emulsions from phytochemicals are potentially useful for treating specific biofilm-related chronic infections.

Microbial diversity and antimicrobial susceptibility in endotracheal tube biofilms recovered from mechanically ventilated COVID-19 patients.

In patients with acute respiratory failure, mechanical ventilation through an endotracheal tube (ET) may be required to correct hypoxemia and hypercarbia. However, biofilm formation on these ETs is a risk factor for infections in intubated patients, as the ET can act as a reservoir of microorganisms that can cause infections in the lungs. As severely ill COVID-19 patients often need to be intubated, a better knowledge of the composition of ET biofilms in this population is important. In Spring 2020, during the first wave of the COVID-19 pandemic in Europe, 31 ETs were obtained from COVID-19 patients at Ghent University Hospital (Ghent, Belgium). Biofilms were collected from the ET and the biofilm composition was determined using culture-dependent (MALDI-TOF mass spectrometry and biochemical tests) and culture-independent (16S and ITS1 rRNA amplicon sequencing) approaches. In addition, antimicrobial resistance was assessed for isolates collected via the culture-dependent approach using disc diffusion for 11 antimicrobials commonly used to treat lower respiratory tract infections. The most common microorganisms identified by the culture-dependent approach were those typically found during lung infections and included both presumed commensal and potentially pathogenic microorganisms like Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa and Candida albicans. More unusual organisms, such as Paracoccus yeei, were also identified, but each only in a few patients. The culture-independent approach revealed a wide variety of microbes present in the ET biofilms and showed large variation in biofilm composition between patients. Some biofilms contained a diverse set of bacteria of which many are generally considered as non-pathogenic commensals, whereas others were dominated by a single or a few pathogens. Antimicrobial resistance was widespread in the isolates, e.g. 68% and 53% of all isolates tested were resistant against meropenem and gentamicin, respectively. Different isolates from the same species recovered from the same ET biofilm often showed differences in antibiotic susceptibility. Our data suggest that ET biofilms are a potential risk factor for secondary infections in intubated COVID-19 patients, as is the case in mechanically-ventilated non-COVID-19 patients.

Piezoelectric hybrid scaffolds mineralized with calcium carbonate for tissue engineering: Analysis of local enzyme and small-molecule drug delivery, cell response and antibacterial performance.

As the next generation of materials for bone reconstruction, we propose a multifunctional bioactive platform based on biodegradable piezoelectric polyhydroxybutyrate (PHB) fibrous scaffolds for tissue engineering with drug delivery capabilities. To use the entire surface area for local drug delivery, the scaffold surface was uniformly biomineralized with biocompatible calcium carbonate (CaCO3) microparticles in a vaterite-calcite polymorph mixture. CaCO3-coated PHB scaffolds demonstrated a similar elastic modulus compared to that of pristine one. However, reduced tensile strength and failure strain of 31% and 67% were observed, respectively. The biomimetic immobilization of enzyme alkaline phosphatase (ALP) and glycopeptide antibiotic vancomycin (VCM) preserved the CaCO3-mineralized PHB scaffold morphology and resulted in partial recrystallization of vaterite to calcite. In comparison to pristine scaffolds, the loading efficiency of CaCO3-mineralized PHB scaffolds was 4.6 and 3.5 times higher for VCM and ALP, respectively. Despite the increased number of cells incubated with ALP-immobilized scaffolds (up to 61% for non-mineralized and up to 36% for mineralized), the CaCO3-mineralized PHB scaffolds showed cell adhesion; those containing both VCM and ALP molecules had the highest cell density. Importantly, no toxicity for pre-osteoblastic cells was detected, even in the VCM-immobilized scaffolds. In contrast with antibiotic-free scaffolds, the VCM-immobilized ones had a pronounced antibacterial effect against gram-positive bacteria Staphylococcus aureus. Thus, piezoelectric hybrid PHB scaffolds modified with CaCO3 layers and immobilized VCM/ALP are promising materials in bone tissue engineering.

Biological activity and antimicrobial property of Cu/a-C:H nanocomposites and nanolayered coatings on titanium substrates.

Infection associated with titanium based implants remains the most serious problem in implant surgery hence it is important to find optimal strategies to prevent infections. In the present study, we investigated the surface properties, antibacterial activity and biocompatibility of nanocomposite coatings based on an amorphous hydrocarbon (a-C:H) film containing copper nanoparticles (CuNPs) deposited on Ti discs via a gas aggregation cluster source. Three different Cu/a-C:H coatings with approximately the same amount of embedded CuNPs with and without barrier a-C:H layer were fabricated. The obtained results revealed that different structures of the produced coatings have significantly different release rates of Cu ions from the coatings into the aqueous media. This subsequently influences the antibacterial efficiency and osteoblast cell viability of the treated coatings. Coatings with the highest number of CuNPs resulted in excellent antibacterial activity exhibiting approximately 4 log reduction of E.coli and S.aureus after 24 h incubation. The cytotoxicity study revealed that after 7 day cell seeding, even the coating with the highest Cu at.% (4 at.%) showed a cell viability of Ì´90%. Consequently, the coating, formed with a properly tailored number of CuNPs and a-C:H barrier thickness offer a strong antibacterial effect without any harm to osteoblast cells.

First Report of Candidemia Clonal Outbreak Caused by Emerging Fluconazole-Resistant Candida parapsilosis Isolates Harboring Y132F and/or Y132F+K143R in Turkey.

Clonal outbreaks of fluconazole-resistant (FLZR) Candida parapsilosis isolates have been reported in several countries. Despite its being the second leading cause of candidemia, the azole resistance mechanisms and the clonal expansion of FLZR C. parapsilosis blood isolates have not been reported in Turkey. In this study, we consecutively collected C. parapsilosis blood isolates (n = 225) from the fifth largest hospital in Turkey (2007 to 2019), assessed their azole susceptibility pattern using CLSI M27-A3/S4, and sequenced ERG11 for all and MRR1, TAC1, and UPC2 for a selected number of C. parapsilosis isolates. The typing resolution of two widely used techniques, amplified fragment length polymorphism typing (AFLP) and microsatellite typing (MST), and the biofilm production of FLZR isolates with and without Y132F were compared. Approximately 27% of isolates were FLZR (60/225), among which 90% (54/60) harbored known mutations in Erg11, including Y132F (24/60) and Y132F+K143R (19/60). Several mutations specific to FLZR isolates were found in MRR1, TAC1, and UPC2 AFLP grouped isolates into two clusters, while MST revealed several clusters. The majority of Y132F/Y132F+K143R isolates grouped in clonal clusters, which significantly expanded throughout 2007 to 2019 in neonatal wards. Candida parapsilosis isolates carrying Y132F were associated with significantly higher mortality and less biofilm production than other FLZR isolates. Collectively, we documented the first outbreak of FLZR C. parapsilosis blood isolates in Turkey. The MRR1, TAC1, and UPC2 mutations exclusively found in FLZR isolates establishes a basis for future studies, which will potentially broaden our knowledge of FLZR mechanisms in C. parapsilosis MST should be a preferred method for clonal analysis of C. parapsilosis isolates in outbreak scenarios.

Fabrication of Microporous Coatings on Titanium Implants with Improved Mechanical, Antibacterial, and Cell-Interactive Properties.

The success of an orthopedic implant therapy depends on successful bone integration and the prevention of microbial infections. In this work, plasma electrolytic oxidation (PEO) was performed to deposit TiO2 coatings enriched with Ca, P, and Ag on titanium to improve its surface properties and antibacterial efficacy while maintaining normal biological functions and thus to enhance the performance of orthopedic implants. After PEO treatment, the surface of Ti was converted to anatase and rutile TiO2, hydroxyapatite, and calcium titanate phases. The presence of these crystalline phases was further increased with an increased Ag content in the coatings. The developed coatings also exhibited a more porous morphology with an improved surface wettability, roughness, microhardness, and frictional coefficient. In vitro antibacterial assays indicated that the Ag-doped coatings can significantly prevent the growth of both Staphylococcus aureus and Escherichia coli by releasing Ag+ ions, and the ability to prevent these bacteria was enhanced by increasing the Ag content in the coatings, resulting in a maximal 6-log reduction of E. coli and a maximal 5-log reduction of S. aureus after 24 h of incubation. Moreover, the in vitro cytocompatibility evaluation of the coatings showed that the osteoblast (MC3T3) cell integration on the PEO-based coatings was greatly improved compared to untreated Ti and no notable impact on their cytocompatibility was observed on increasing the amount of Ag in the coating. In conclusion, the coating with favorable physicochemical and mechanical properties along with controlled silver ion release can offer an excellent antibacterial performance and osteocompatibility and can thus become a prospective coating strategy to face current challenges in orthopedics.

Investigation of Ag/a-C:H Nanocomposite Coatings on Titanium for Orthopedic Applications.

One of the leading causes of failure for any bone implant is implant-associated infections. The implant-bone interface is in fact the crucial site of infection where both the microorganisms and cells compete to populate the newly introduced implant surface. Most of the work dealing with this issue has focused on the design of implant coatings capable of preventing infection while ignoring cell proliferation or vice versa. The present study is therefore focused on investigating the antibacterial and biological properties of nanocomposite coatings based on an amorphous hydrocarbon (a-C:H) matrix containing silver nanoparticles (AgNPs). a-C:H coatings with varying silver concentrations were generated directly on medical grade titanium substrates using a combination of a gas aggregation source (GAS) and a plasma-enhanced chemical vapor deposition (PE-CVD) process. The obtained results revealed that the surface silver content increased from 1.3 at % to 5.3 at % by increasing the used DC magnetron current in the GAS from 200 to 500 mA. The in vitro antibacterial assays revealed that the nanocomposites with the highest number of silver content exhibited excellent antibacterial activities resulting in a 6-log reduction of Escherichia coli and a 4-log reduction of Staphylococcus aureus after 24 h of incubation. An MTT assay, fluorescence live/dead staining, and SEM microscopy observations of MC3T3 cells seeded on the uncoated and coated Ti substrates also showed that increasing the amount of AgNPs in the nanocomposites had no notable impact on their cytocompatibility, while improved cell proliferation was especially observed for the nanocomposites possessing a low amount of AgNPs. These controllable Ag/a-C:H nanocomposites on Ti substrates, which simultaneously provide an excellent antibacterial performance and good biocompatibility, could thus have promising applications in orthopedics and other biomedical implants.

Influence of the Aliphatic Side Chain on the Near Atmospheric Pressure Plasma Polymerization of 2-Alkyl-2-oxazolines for Biomedical Applications.

Plasma polymerization is gaining popularity as a technique for coating surfaces due to the low cost, ease of operation, and substrate-independent nature. Recently, the plasma polymerization (or deposition) of 2-oxazoline monomers was reported resulting in coatings that have potential applications in regenerative medicine. Despite the structural versatility of 2-oxazolines, only a few monomers have been subjected to plasma polymerization. Within this study, however, we explore the near atmospheric pressure plasma polymerization of a range of 2-oxazoline monomers, focusing on the influence of the aliphatic side-chain length (methyl to butyl) on the plasma polymerization process conditions as well as the properties of the obtained coatings. While side-chain length had only a minor influence on the chemical composition, clear effects on the plasma polymerization conditions were observed, thus gaining valuable insights in the plasma polymerization process as a function of monomer structure. Additionally, cytocompatibility and cell attachment on the coatings obtained by 2-oxazoline plasma polymerization was assessed. The coatings displayed strong cell interactive properties, whereby cytocompatibility increased with increasing aliphatic side-chain length of the monomer, reaching up to 93% cell viability after 1 day of cell culture compared to tissue culture plates. As this is in stark contrast to the antifouling behavior of the parent polymers, we compared the properties and composition of the plasma-polymerized coatings to the parent polymers revealing that a significantly different coating structure was obtained by plasma polymerization.

Lipid-Based Quaternary Ammonium Sophorolipid Amphiphiles with Antimicrobial and Transfection Activities.

Twelve new quaternary ammonium sophorolipids with long alkyl chains on the nitrogen atom were synthesized starting from oleic and petroselinic acid-based sophorolipids. These novel derivatives were evaluated for their antimicrobial activity against selected Gram-negative and Gram-positive bacteria and their transfection efficacies on three different eukaryotic cell lines in vitro as good activities were demonstrated for previously synthesized derivatives. Self-assembly properties were also evaluated. All compounds proved to possess antimicrobial and transfection properties, and trends could be observed based on the length of the nitrogen substituent and the total length of the sophorolipid tail. Moreover, all long-chain quaternary ammonium sophorolipids form micelles, which proved to be a prerequisite to induce antimicrobial activity and transfection capacity. These results are promising for future healthcare applications of long-chained quaternary ammonium sophorolipids.

The Antimicrobial Peptide lin-SB056-1 and Its Dendrimeric Derivative Prevent Pseudomonas aeruginosa Biofilm Formation in Physiologically Relevant Models of Chronic Infections.

Antimicrobial peptides (AMPs) are promising templates for the development of novel antibiofilm drugs. Despite the large number of studies on screening and optimization of AMPs, only a few of these evaluated the antibiofilm activity in physiologically relevant model systems. Potent in vitro activity of AMPs often does not translate into in vivo effectiveness due to the interference of the host microenvironment with peptide stability/availability. Hence, mimicking the complex environment found in biofilm-associated infections is essential to predict the clinical potential of novel AMP-based antimicrobials. In the present study, we examined the antibiofilm activity of the semi-synthetic peptide lin-SB056-1 and its dendrimeric derivative (lin-SB056-1)2-K against Pseudomonas aeruginosa in an in vivo-like three-dimensional (3-D) lung epithelial cell model and an in vitro wound model (consisting of an artificial dermis and blood components at physiological levels). Although moderately active when tested alone, lin-SB056-1 was effective in reducing P. aeruginosa biofilm formation in association with 3-D lung epithelial cells in combination with the chelating agent EDTA. The dimeric derivative (lin-SB056-1)2-K demonstrated an enhanced biofilm-inhibitory activity as compared to both lin-SB056-1 and the lin-SB056-1/EDTA combination, reducing the number of biofilm-associated bacteria up to 3-Log units at concentrations causing less than 20% cell death. Biofilm inhibition by (lin-SB056-1)2-K was reported both for the reference strain PAO1 and cystic fibrosis lung isolates of P. aeruginosa. In addition, using fluorescence microscopy, a significant decrease in biofilm-like structures associated with 3-D cells was observed after peptide exposure. Interestingly, effectiveness of (lin-SB056-1)2-K was also demonstrated in the wound model with a reduction of up to 1-Log unit in biofilm formation by P. aeruginosa PAO1 and wound isolates. Overall, combination treatment and peptide dendrimerization emerged as promising strategies to improve the efficacy of AMPs, especially under challenging host-mimicking conditions. Furthermore, the results of the present study underlined the importance of evaluating the biological properties of novel AMPs in in vivo-like model systems representative of specific infectious sites in order to make a more realistic prediction of their therapeutic success, and avoid the inclusion of unpromising peptides in animal studies and clinical trials.

Detection and quantification of Enterococcus faecalis RNPP-type quorum sensing peptides in bacterial culture media by UHPLC-MS.

Bacteria communicate with each other using quorum sensing; i.e. the production and sensing of signalling molecules. Enterococcus faecalis, a Gram-positive bacterium, employs peptides as quorum sensing molecules. These peptides have previously been isolated from culture media by elaborate, time and medium-consuming sample preparation approaches and specific bacteria-based bio-sensors. Here, a method for the detection and quantification of all nine currently reported E. faecalis quorum sensing peptides belonging to the RNPP family in bacterial cell culture medium was developed. The approach developed consists of solid-phase extraction (SPE) sample preparation followed by a UHPLC-triple quadrupole mass spectroscopic method, operated in Multiple Reaction Monitoring (MRM) mode. All nine peptides were quantified with a total analysis time below 90 min per sample and limited cell culture medium volumes of only 1 ml per sample. A method verification, performed in uniplicate, was carried out to obtain an idea of the method performance. The recovery varied between 19.9 and 119.0%, and the limit of detection is in the low nM range. Analytical stability, carry-over and dilution integrity were investigated and were acceptable. This method will be a useful tool in the investigation of the roles of the RNPP-type quorum sensing peptides in microbial processes.

Community Composition Determines Activity of Antibiotics against Multispecies Biofilms.

In young cystic fibrosis (CF) patients, Staphylococcus aureus is typically the most prevalent organism, while in adults, Pseudomonas aeruginosa is the major pathogen. More recently, it was observed that also Streptococcus anginosus plays an important role in exacerbations of respiratory symptoms. These species are often coisolated from CF lungs, yet little is known about whether antibiotic killing of one species is influenced by the presence of others. In the present study, we compared the activities of various antibiotics against S. anginosus, S. aureus, and P. aeruginosa when grown in monospecies biofilms with the activity observed in a multispecies biofilm. Our results show that differences in antibiotic activity against species grown in mono- and multispecies biofilms are species and antibiotic dependent. Fewer S. anginosus cells are killed by antibiotics that interfere with cell wall synthesis (amoxicillin plus sulbactam, cefepime, imipenem, meropenem, and vancomycin) in the presence of S. aureus and P. aeruginosa, while for ciprofloxacin, levofloxacin, and tobramycin, no difference was observed. In addition, we observed that the cell-free supernatant of S. aureus, but not that of P. aeruginosa biofilms, also caused this decrease in killing. Overall, S. aureus was more affected by antibiotic treatment in a multispecies biofilm, while for P. aeruginosa, no differences were observed between growth in mono- or multispecies biofilms. The results of the present study suggest that it is important to take the community composition into account when evaluating the effect of antimicrobial treatments against certain species in mixed biofilms.

Antimicrobial efficacy against Pseudomonas aeruginosa biofilm formation in a three-dimensional lung epithelial model and the influence of fetal bovine serum.

In vitro models that mimic in vivo host-pathogen interactions are needed to evaluate candidate drugs that inhibit bacterial virulence traits. We established a new approach to study Pseudomonas aeruginosa biofilm susceptibility on biotic surfaces, using a three-dimensional (3-D) lung epithelial cell model. P. aeruginosa formed antibiotic resistant biofilms on 3-D cells without affecting cell viability. The biofilm-inhibitory activity of antibiotics and/or the anti-biofilm peptide DJK-5 were evaluated on 3-D cells compared to a plastic surface, in medium with and without fetal bovine serum (FBS). In both media, aminoglycosides were more efficacious in the 3-D cell model. In serum-free medium, most antibiotics (except polymyxins) showed enhanced efficacy when 3-D cells were present. In medium with FBS, colistin was less efficacious in the 3-D cell model. DJK-5 exerted potent inhibition of P. aeruginosa association with both substrates, only in serum-free medium. DJK-5 showed stronger inhibitory activity against P. aeruginosa associated with plastic compared to 3-D cells. The combined addition of tobramycin and DJK-5 exhibited more potent ability to inhibit P. aeruginosa association with both substrates. In conclusion, lung epithelial cells influence the efficacy of most antimicrobials against P. aeruginosa biofilm formation, which in turn depends on the presence or absence of FBS.

Evaluation of combination therapy for Burkholderia cenocepacia lung infection in different in vitro and in vivo models.

Burkholderia cenocepacia is an opportunistic pathogen responsible for life-threatening infections in cystic fibrosis patients. B. cenocepacia is extremely resistant towards antibiotics and therapy is complicated by its ability to form biofilms. We investigated the efficacy of an alternative antimicrobial strategy for B. cenocepacia lung infections using in vitro and in vivo models. A screening of the NIH Clinical Collection 1&2 was performed against B. cenocepacia biofilms formed in 96-well microtiter plates in the presence of tobramycin to identify repurposing candidates with potentiator activity. The efficacy of selected hits was evaluated in a three-dimensional (3D) organotypic human lung epithelial cell culture model. The in vivo effect was evaluated in the invertebrate Galleria mellonella and in a murine B. cenocepacia lung infection model. The screening resulted in 60 hits that potentiated the activity of tobramycin against B. cenocepacia biofilms, including four imidazoles of which econazole and miconazole were selected for further investigation. However, a potentiator effect was not observed in the 3D organotypic human lung epithelial cell culture model. Combination treatment was also not able to increase survival of infected G. mellonella. Also in mice, there was no added value for the combination treatment. Although potentiators of tobramycin with activity against biofilms of B. cenocepacia were identified in a repurposing screen, the in vitro activity could not be confirmed nor in a more sophisticated in vitro model, neither in vivo. This stresses the importance of validating hits resulting from in vitro studies in physiologically relevant model systems.

Screening a repurposing library for potentiators of antibiotics against Staphylococcus aureus biofilms.

Staphylococcus aureus biofilms are involved in a wide range of infections that are extremely difficult to treat with conventional antibiotic therapy. We aimed to identify potentiators of antibiotics against mature biofilms of S. aureus Mu50, a methicillin-resistant and vancomycin-intermediate-resistant strain. Over 700 off-patent drugs from a repurposing library were screened in combination with vancomycin in a microtitre plate (MTP)-based biofilm model system. This led to the identification of 25 hit compounds, including four phenothiazines among which thioridazine was the most potent. Their activity was evaluated in combination with other antibiotics both against planktonic and biofilm-grown S. aureus cells. The most promising combinations were subsequently tested in an in vitro chronic wound biofilm infection model. Although no synergistic activity was observed against planktonic cells, thioridazine potentiated the activity of tobramycin, linezolid and flucloxacillin against S. aureus biofilm cells. However, this effect was only observed in a general biofilm model and not in a chronic wound model of biofilm infection. Several drug compounds were identified that potentiated the activity of vancomycin against biofilms formed in a MTP-based biofilm model. A selected hit compound lost its potentiating activity in a model that mimics specific aspects of wound biofilms. This study provides a platform for discovering and evaluating potentiators against bacterial biofilms and highlights the necessity of using relevant in vitro biofilm model systems.

Optimization of resazurin-based viability staining for quantification of microbial biofilms.

The resazurin-based viability staining is often used to quantify viable biofilm cells grown in microtiter plates (MTP). The non-fluorescent resazurin is reduced by metabolically active cells to resorufin which is fluorescent. The amount of fluorescence generated is related to the number of viable cells present. Unfortunately, the linear range of the method is restricted and the lower limit of quantification is approximately 10(6) colony forming units (CFU) per biofilm. The goal of the present study was to optimize this method to broaden its applicability. We added fresh growth medium and resazurin to mature Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia cenocepacia and Candida albicans biofilms formed in MTP. Subsequently, the increase in resazurin-based fluorescence was followed over time and we determined the time needed to reach a specific value of fluorescence as well as the time to reach the maximum fluorescence. These time points correlate with the number of viable cells that were initially present and results were compared to plate counts. Using these alternative read-outs, we were able to extend the linear range from 10(6)-10(8) to 10(3)-10(8) CFU per biofilm, meaning that lower numbers of viable cells can be measured and the effect of anti-biofilm treatments can be quantified more accurately. Moreover, this approach is less expensive and less laborious than conventional plating techniques.

Genomewide screening for genes involved in biofilm formation and miconazole susceptibility in Saccharomyces cerevisiae.

Infections related to fungal biofilms are difficult to treat due to the reduced susceptibility of sessile cells to most antifungal agents. Previous research has shown that 1-10% of sessile Candida cells survive treatment with high doses of miconazole (a fungicidal imidazole). The aim of this study was to identify genes involved in fungal biofilm formation and to unravel the mechanisms of resistance of these biofilms to miconazole. To this end, a screening of a Saccharomyces cerevisiae deletion mutant bank was carried out. Our results revealed that genes involved in peroxisomal transport and the biogenesis of the respiratory chain complex IV play an essential role in biofilm formation. On the other hand, genes involved in transcription and peroxisomal and mitochondrial organization seem to highly influence the susceptibility to miconazole of yeast biofilms. Additionally, our data confirm previous findings on genes involved in biofilm formation and in general stress responses. Our data suggest the involvement of peroxisomes in biofilm formation and miconazole resistance in fungal biofilms.

Eradication of Propionibacterium acnes biofilms by plant extracts and putative identification of icariin, resveratrol and salidroside as active compounds.

Propionibacterium acnes is a Gram-positive bacterium that plays an important role in the pathogenesis of acne vulgaris. This organism is capable of biofilm formation and the decreased antimicrobial susceptibility of biofilm-associated cells may hamper efficient treatment. In addition, the prolonged use of systemic antibiotic therapy is likely to lead to the development and spread of antimicrobial resistance. In the present study we investigated whether P. acnes biofilms could be eradicated by plant extracts or their active compounds, and whether other mechanisms besides killing of biofilm cells could be involved. Out of 119 plant extracts investigated, we identified five with potent antibiofilm activity against P. acnes (extracts from Epimedium brevicornum, Malus pumila, Polygonum cuspidatum, Rhodiola crenulata and Dolichos lablab). We subsequently identified icariin, resveratrol and salidroside as active compounds in three of these extracts. Extracts from E. brevicornum and P. cuspidatum, as well as their active compounds (icariin and resveratrol, respectively) showed marked antibiofilm activity when used in subinhibitory concentrations, indicating that killing of microbial cells is not their only mode of action.