Understanding Biofilms and Novel Approaches to the Diagnosis, Prevention, and Treatment of Medical Device-Associated Infections

Bacterial Biofilm Formation Using PCL/Curcumin Electrospun Fibers and Its Potential Use for Biotechnological Applications

Electrospun nanofibers are used for many applications due to their large surface area, mechanical properties, and bioactivity. Bacterial biofilms are the cause of numerous problems in biomedical devices and in the food industry. On the other hand, these bacterial biofilms can produce interesting metabolites. Hence, the objective of this study is to evaluate the efficiency of poly (Ɛ- caprolactone)/Curcumin (PCL/CUR) nanofibers to promote bacterial biofilm formation. These scaffolds were characterized by scanning electron microscopy (SEM), which showed homogeneous fibers with diameters between 441-557 nm; thermogravimetric analysis and differential scanning calorimetry (TGA and DSC) demonstrated high temperature resilience with degradation temperatures over >350 °C; FTIR and ¹H-NMR serve as evidence of CUR incorporation in the PCL fibers. PCL/CUR scaffolds successfully promoted the formation of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa biofilms. These results will be valuable in the study of controlled harvesting of pathogenic biofilms as well as in metabolites production for biotechnological purposes.

Polyurethane-Based Coatings with Promising Antibacterial Properties

In coatings technology, the possibility of introducing specific characteristics at the surface level allows for the manufacture of medical devices with efficient and prolonged antibacterial properties. This efficiency is often achieved by the use of a small amount of antibacterial molecules, which can fulfil their duty while limiting eventual releasing problems. The object of this work was the preparation and characterization of silver, titanium dioxide and chitosan polyurethane-based coatings. Coatings with the three antibacterials were prepared using different deposition techniques, using a brush or a bar coater automatic film applicator, and compared to solvent casted films prepared with the same components. For silver containing materials, an innovative strategy contemplating the use and preparation of silver nanoparticles in a single step-method was employed. This preparation was obtained starting from a silver precursor and using a single compound as the reducing agent and stabilizer. Ultraviolet-visible spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, contact angle measurements and adhesion test experiments were used to characterize the prepared coatings. Promising antibacterial properties, measured via direct and indirect methods, were registered for all the silver-based materials.

Alcohol dehydrogenase modulates quorum sensing in biofilm formations of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a common opportunistic nosocomial pathogen, which is able to produce biofilms on the surface of indwelling medical devices, and consequentially causes severe infections in clinical settings. In order to identify genes that involved in the biofilm formation of A. baumannii, the differential expression of genes between biofilms and planktonic cells was analyzed by RNAseq assay and validated in clinical isolates. The RNAseq data showed that 264 genes were up-regulated, while 240 genes were down-regulated in the biofilms of A. baumannii. Among them, the gene encoding alcohol dehydrogenase (ADH), a known molecule of bacterial quorum sensing (QS) system that plays a key role in biofilm formation bacteria, was one of the most up-regulated gene in both reference strains and clinical isolates. Functional studies using ADH inhibitor disulfiram and activator taurine further demonstrated that the presence of disulfiram significantly inhibit the cell growth, motility and biofilm formation, paralleled by a decreased expression of QS-related genes, including AbaI, A1S_0109, and A1S_0112, in a dose-dependent manner; vice versa, the addition of ADH activator taurine, and QS molecule C12- homoserine lactone synthase (HSL) led a dose-dependent increase of bacterial growth, motility and biofilm production, along with an increased expression of QS-related genes in both reference strains and clinical isolates of A. baumannii. These results suggested that the ADH was a key molecule able to modulate the QS system and promote the biofilm formation, growth and motility in A. baumannii.

Antimicrobial action of 1,10-phenanthroline-based compounds on carbapenemase-producing Acinetobacter baumannii clinical strains: efficacy against planktonic- and biofilm-growing cells

Therapeutic options are limited for patients infected with Acinetobacter baumannii due to its multidrug-resistance profile. So, the search for new antimicrobials against this gram-negative bacterial pathogen has become a worldwide priority. The present study aimed to evaluate the effects of 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendione), [Ag(phendione)₂]ClO₄ (Ag-phendione) and [Cu(phendione)₃](ClO₄)₂·4H₂O (Cu-phendione) on 26 carbapenemase-producing A. baumannii strains. The susceptibility to carbapenems was performed by detecting the metallo-beta-lactamase (MBL) genes by PCR and by determining the MIC. Also, disk diffusion method was applied to evaluate the susceptibility to other antimicrobial classes. The test compounds were evaluated on both planktonic- and biofilm-growing bacterial cells. The results revealed that all A. baumannii strains had the intrinsic bla_oxa-51 gene, and at least one of the bla_oxa-23 or bla_oxa-24 genes. The geometric mean MIC and minimum bactericidal concentration (MBC) values, respectively, were as follows: Cu-phendione (1.56 and 2.30 μM), Ag-phendione (2.48 and 3.63 μM), phendione (9.44 and 9.70 μM), and phen (70.46 and 184.28 μM). The test compounds (at 0.5 × MIC) affected the biofilm formation and disrupted the mature biofilm, in a typically dose-dependent manner, reducing biomass and viability parameters. Collectively, silver and copper-phendione derivatives presented potent antimicrobial action against planktonic- and biofilm-forming cells of carbapenemase-producing A. baumannii.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Biofilm and Chronic Nonhealing Wound Infections

In this review, the author summarizes the role of biofilm formation in chronic nonhealing wound infections along with characteristics of biofilm formation, diagnosis, detection, and treatment. Because biofilms are still not clearly understood, treatment and diagnosis are currently difficult.

Activated Polyhydroxyalkanoate Meshes Prevent Bacterial Adhesion and Biofilm Development in Regenerative Medicine Applications

Regenerative medicine has become an extremely valuable tool offering an alternative to conventional therapies for the repair and regeneration of tissues. The re-establishment of tissue and organ functions can be carried out by tissue engineering strategies or by using medical devices such as implants. However, with any material being implanted inside the human body, one of the conundrums that remains is the ease with which these materials can get contaminated by bacteria. Bacterial adhesion leads to the formation of mature, alive and complex three-dimensional biofilm structures, further infection of surrounding tissues and consequent development of complicated chronic infections. Hence, novel tissue engineering strategies delivering biofilm-targeted therapies, while at the same time allowing tissue formation are highly relevant. In this study our aim was to develop surface modified polyhydroxyalkanoate-based fiber meshes with enhanced bacterial anti-adhesive and juvenile biofilm disrupting properties for tissue regeneration purposes. Using reactive and amphiphilic star-shaped macromolecules as an additive to a polyhydroxyalkanoate spinning solution, a synthetic antimicrobial peptide, Amhelin, with strong bactericidal and anti-biofilm properties, and Dispersin B, an enzyme promoting the disruption of exopolysaccharides found in the biofilm matrix, were covalently conjugated to the fibers by addition to the solution before the spinning process. Staphylococcus epidermidis is one of the most problematic pathogens responsible for tissue-related infections. The initial antibacterial screening showed that Amhelin proved to be strongly bactericidal at 12 μg/ml and caused >50% reductions of biofilm formation at 6 μg/ml, while Dispersin B was found to disperse >70% of pre-formed biofilms at 3 μg/ml. Regarding the cytotoxicity of the agents toward L929 murine fibroblasts, a CC50 of 140 and 115 μg/ml was measured for Amhelin and Dispersin B, respectively. Optimization of the electrospinning process resulted in aligned fibers. Surface activated fibers with Amhelin and Dispersin B resulted in 83% reduction of adhered bacteria on the surface of the fibers. Additionally, the materials developed were found to be cytocompatible toward L929 murine fibroblasts. The strategy reported in this preliminary study suggests an alternative approach to prevent bacterial adhesion and, in turn biofilm formation, in materials used in regenerative medicine applications such as tissue engineering.

Pentadecanal and pentadecanoic acid coatings reduce biofilm formation of Staphylococcus epidermidis on PDMS

Staphylococcus epidermidis is well known to be one of the major causes of infections related to medical devices, mostly due to its strong capacity to form device-associated biofilms. Nowadays, these infections represent a severe burden to the public health system and the necessity of novel antibacterial strategies for the treatment of these difficult-to-eradicate infections is urgent. The Antarctic marine bacterium Pseudoalteromonas haloplanktis TAC125 was found to be able to produce an anti-biofilm molecule, the pentadecanal, active against S. epidermidis. In this work, we modified one of the most widely used silicone-based polymers, polydimethylsiloxane (PDMS), by adsorption of pentadecanal and its most promising derivative, pentadecanoic acid, on the PDMS surface. The biofilm formation of S. epidermidis RP62A on both untreated and modified PDMS was performed in a parallel plate flow chamber system, demonstrating the capability of the proposed anti-biofilm coatings to strongly reduce the biofilm formation. Furthermore, drug-release capacity and long-term efficacy (21 days) were also proven for the pentadecanoic acid coating.

Differential Susceptibility of Catheter Biomaterials to Biofilm-Associated Infections and Their Remedy by Drug-Encapsulated Eudragit RL100 Nanoparticles

Biofilms are the cause of major bacteriological infections in patients. The complex architecture of Escherichia coli (E. coli) biofilm attached to the surface of catheters has been studied and found to depend on the biomaterial's surface properties. The SEM micrographs and water contact angle analysis have revealed that the nature of the surface affects the growth and extent of E. coli biofilm formation. In vitro studies have revealed that the Gram-negative E. coli adherence to implanted biomaterials takes place in accordance with hydrophobicity, i.e., latex > silicone > polyurethane > stainless steel. Permanent removal of E. coli biofilm requires 50 to 200 times more gentamicin sulfate (G-S) than the minimum inhibitory concentration (MIC) to remove 90% of E. coli biofilm (MBIC90). Here, in vitro eradication of biofilm-associated infection on biomaterials has been done by Eudragit RL100 encapsulated gentamicin sulfate (E-G-S) nanoparticle of range 140 nm. It is 10-20 times more effective against E. coli biofilm-associated infections eradication than normal unentrapped G-S. Thus, Eudragit RL100 mediated drug delivery system provides a promising way to reduce the cost of treatment with a higher drug therapeutic index.