pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

Application of phage-derived enzymes for enhancing food safety

Foodborne pathogens such as Salmonella, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus present significant public health threats, causing widespread illness and economic loss. Contaminated food is responsible for an estimated 600 million illnesses and 420,000 deaths annually, with low- and middle-income countries facing losses of approximately $110 billion each year. Traditional methods to ensure food safety, including antimicrobials and preservatives, can contribute to the development of antimicrobial-resistant bacteria, highlighting the need for alternative strategies. Bacteriophages are gaining renewed attention as promising alternatives to conventional antibiotics due to their specifically target bacteria and their lower potential for causing adverse effects. However, their practical application is limited by challenges such as narrow host ranges, the emergence of phage-resistant bacteria, and stability issues. Recent research has shifted focus towards phage-derived enzymes, including endolysins, depolymerases, holins, and spanins, which are involved in the phage lytic cycle. These enzymes, as potential approaches to food safety, have demonstrated significant efficacy in targeting and lysing bacterial pathogens, making them suitable for controlling foodborne pathogens and preventing foodborne illnesses. Phage-derived enzymes also show promise in controlling biofilms and enhancing antimicrobial activity when combined with other antimicrobials. Therefore, this review emphasizes recent advancements in the use of the phage-derived enzymes for food safety, addresses their limitations, and suggests strategies to enhance their effectiveness in food processing and storage environments.

Functionalization of Biomimetic Polydopamine Shells Constructed onto Bismuth-Core Particles for pH-Mediated Drug Targeting to Heal Bacterial Infections

Nonhealing chronic bacterial infections are very challenging to both patients and the healthcare-providing system. Multimodal therapy enhances the antibiotic efficacy to treat infections via combating multidrug resistance through cumulative therapeutic effects. Functionalized polydopamine (PDA)-coated Bi particles having a core-shell structure may treat such chronic infections. We fabricated a new advanced material based on Tris-functionalized PDA and Bi using a facile three-step protocol for healing drug-resistant bacterial infections. The fabrication of Bi particles, PDA coating on Bi particles, and their Tris functionalization were confirmed by X-ray diffraction, and spectroscopic and thermogravimetric analyses. Tris-functionalized PDA-coated Bi particles, abbreviated as Bi/PDA-Tris, exhibited a higher average diameter, improved hydrophilicity, aqueous dispersity, and colloidal stability. Bi/PDA-Tris showed a delicate surface morphology, narrow size distribution, spherical shape, and core-shell structure. In vitro bovine serum albumin and hemolysis assays showed minimal protein adsorption and the desirable hemocompatibility of Bi/PDA-Tris. Antibacterial gentamicin (GM)-immobilized Bi/PDA-Tris showed pH-mediated sustained drug release kinetics under acidic conditions. The in vitro study of GM-loaded Bi/PDA-Tris particles exhibited significant bacterial growth inhibition and bactericidal activity. Tris functionalization effectively enhances the antibacterial efficacy of the PDA shell under acidic conditions to target and heal bacterial infections. This approach has introduced economic, nontoxic, easy-to-use, relatively more biocompatible Bi particles as a substituent for precise metals like Pt, Au, and Ag for the development of core-shell composite materials.

The rational design, biofunctionalization and biological properties of orthopedic porous titanium implants: a review

Porous titanium implants are becoming an important tool in orthopedic clinical applications. This review provides a comprehensive survey of recent advances in porous titanium implants for orthopedic use. First, the review briefly describes the characteristics of bone and the design requirements of orthopedic implants. Subsequently, the pore size and structural design of porous titanium alloy materials are presented, then we introduce the application of porous titanium alloy implants in orthopedic clinical practice, including spine surgery, joint surgery, and the treatment of bone tumors. Following that, we describe the surface modifications applied to porous titanium implants to obtain better biological functions. Finally, we discuss incorporating environmental responsive mechanisms into porous titanium alloy materials to achieve additional functionalities.

Unraveling the Applicability of LbL Coatings for Drug Delivery in Dental Implant-Related Infection Treatment

Peri-implantitis is an inflammatory condition caused by bacterial biofilms adhered on dental implant surfaces that cause progressive tissue destruction from the host's inflammatory response. The adverse effects of peri-implantitis progression can go beyond just losing the implant. This highlights the importance of implementing strategies to stabilize disease in the short term. Layer-by-layer (LbL) assembly is a promising avenue in the field of peri-implantitis management due to its applicability with a variety of substances, in addition to being an easy, versatile, and flexible process for multilayer formation to act directly in the affected site. In this Review, our objective is to offer comprehensive chemical and biological insights into the LbL system, clarifying its specific application as antimicrobial coatings, with concern for the physical site and purpose. Additionally, we delve deeper into the concepts of onset and progression of peri-implantitis, aiming to elucidate the precise indications for employing the LbL system as a coating for implant abutments in peri-implantitis treatment. Finally, we correlate the chemical composition of the LbL system with its functionality while also addressing the challenges posed by the uncontrolled environment of the oral cavity, which ultimately restricts its clinical applicability.

Local antimicrobial delivery systems for prophylaxis and treatment of periprosthetic traumatological infections

Infections associated with implants are the most serious complications in joint replacement surgeries and can jeopardize the functionality of orthopedic implants. Local antimicrobial delivery could enable antibiotics to attain concentrations above the minimum inhibitory concentration (MIC) threshold at the joint replacement site while preventing systemic side effects. Therefore, there is a dire need for the development of improved biomaterial-based delivery systems for local antibiotic administration in prosthetic infections. In this context, this review highlights the latest breakthroughs in the design of biomaterial-based formulations intended for the prophylaxis and treatment of prosthetic infections. Delivery systems for distinct forms of administration (i.e., direct intra-articular administration, loading into bone cements, coating of implant surfaces, or loading into hydrogels) are here comprehensively compiled with a focus on the design of microparticles and nanosystems for local antimicrobial administration and their impact on distinct in vitro and in vivo models of implant infections.

Tuning the Localized Microenvironment near a Continuous Glucose Meter to Ensure Monitoring Accuracy and Longevity by Plasma-Induced Grafting Zwitterionic Brushes

Diabetes mellitus is a metabolic disorder that affects millions of individuals worldwide. Continuous glucose monitoring (CGM) offers a prevalent method for continuously monitoring interstitial glucose levels instead of traditional self-monitoring of blood glucose (BG), eliminating the need for finger pricking and providing only discrete data. However, challenges in accuracy persist in CGM, including substantial noise interference and tissue fluid erosion, as well as the pH fluctuations in the localized ISF microenvironment during acute inflammation periods. Herein, we reported a facile atmospheric plasma-induced grafting technique to surface functionalize a zwitterionic brush coating on the sensor, with the aim to adjust the sensor's microenvironmental chemistry. The zwitterionic brush-coated CGM (Z-coated CGM) could regulate pH values with a good glucose response in the pH range from 6.2 to 7.6 and a prolonged sensor life over the uncoated sensor. We evaluated the rat practice that the Z-coated CGM consistently outperformed the uncoated in tracking BG fluctuations, with higher correlation coefficients and significant noise reduction for both non-recalibration and recalibration. This technology holds substantial implications for subcutaneous embedded glucose monitors and facilitates CGMs in achieving independence from routine BG fingerstick calibrations.

Bioactive Composition of Tropical Flowers and Their Antioxidant and Antimicrobial Properties

This study evaluated tropical flower petals' bioactive compounds and antioxidant and antimicrobial properties. The physicochemical characteristics, carotenoids, phenolics, anthocyanins, organic acids, and antioxidant activity of 67 flowers were analyzed. In addition, the antimicrobial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus mutans, Candida albicans, and Candida tropicalis of 35 species was determined. A 2 × 3 experimental design was used for the extraction of carotenoids and phenolics, including solvents and ultrasonic agitation times. The mixture of methanol-acetone-dichloromethane (1:1:2) and acetone-methanol (2:1) resulted in the highest concentration of carotenoids, while acidified 80% methanol favoured phenolic extraction. Renealmia alpinia was extremely rich in carotenoids (292.5 mg β-carotene/g DW), Pleroma heteromallum in anthocyanins (7.35 mg C-3-gl/g DW), while a high content of citric acid was found in Hibiscus rosa-sinensis (17,819 mg/100 g DW). On the other hand, Thibaudia floribunda showed the highest antioxidant activity (7.8 mmol Trolox equivalent/g DW). The main phenolics were m-coumaric acid in Acalypha poiretii (12,044 mg/100 g DW), 4-hydroxybenzoic acid in Brugmansia arborea (10,729 mg/100 g DW), and kaempferol in Dahlia pinnata (8236 mg/100 g DW). The extract of Acalypha poiretii, Brownea macrophylla, and Cavendishia nobilis showed antibacterial activity, while the extract of Pleroma heteromallum was the only one active against Candida albicans. These findings highlight the potential health benefits from certain tropical flowers.

Impact of acidic and alkaline conditions on Staphylococcus aureus and Acinetobacter baumannii interactions and their biofilms

Bacterial biofilms pose significant challenges due to their association with antibiotic resistance, metabolic adaptation, and survival under harsh conditions. Among notable pathogens forming biofilms, Staphylococcus aureus and Acinetobacter baumannii are concerning pathogens in nosocomial settings. However, their behaviour under acidic (pH 4.5) and alkaline (pH10.5) conditions, especially in co-culture setups, remains insufficiently understood. This study investigates these aspects, by examining growth rates, biofilm formation, pH shifts, phenotypic analysis, and gene expression profiles. The results showed A. baumannii exhibited reduced  growth and biofilm formation at pH 4.5, while S. aureus showed slow growth and low biofilm formation at pH10.5 in mono-cultures. S. aureus leaned towards an acidic pH (6-6.5), whereas A. baumannii shifted towards an alkaline pH (8-9). In co-culture environments, growth rates and biofilm formation increased across all pH conditions, converging towards a neutral pH over time. Phenotypic motility assays indicated that A. baumannii exhibited greater motility in alkaline conditions, while S. aureus showed increased staphyloxanthin production under acidic conditions. Gene expression analyses revealed that the fibronectin-binding protein A (FnbA) and N-acetylglucosaminyl-transferase (icaA) genes, responsible for initial attachment during biofilm formation, were highly expressed in acidic co-culture condition but poorly expressed in alkaline condition. In A. baumannii, the outer membrane protein A (OmpA) gene associated with adhesion and virulence, was upregulated in co-culture. The LuxR gene involved in quorum sensing was upregulated in acidic conditions and poorly expressed at pH 10.5. This study elucidates the metabolic adaptability and biofilm formation tendencies of S. aureus towards acidic conditions and A. baumannii towards alkaline conditions, providing insights for better management of biofilm-related infections.

Antimicrobial Sub-MIC induces Staphylococcus aureus biofilm formation without affecting the bacterial count

BACKGROUND

Biofilm formation is an essential virulence factor that creates a highly protected growth mode for Staphylococcus aureus (S. aureus) to survive in any hostile environment. Antibiotic sub-minimal inhibitory concentration (sub-MIC) may modulate the biofilm formation ability of bacterial pathogens, thereby affecting bacterial pathogenesis and infection outcomes. Intense antimicrobial therapy to treat biofilm-associated infections can control the pathogenic infection aggravation but cannot guarantee its complete eradication.

OBJECTIVE

This study aimed to assess the sub-MICs effect of 5 different antimicrobial classes on biofilm-forming capacity among Staphylococcus aureus clinical isolates using three different biofilm quantitation techniques.

METHODS

In this study, the effects of 5 different antimicrobial agents, namely, azithromycin, gentamicin, ciprofloxacin, doxycycline, and imipenem, at sub-MICs of 12.5%, 25%, and 50% were tested on 5 different clinical isolates of S. aureus. The biofilms formed in the absence and presence of different antimicrobial sub-MICs were then assessed using the following three different techniques: the crystal violet (CV) staining method, the quantitative PCR (qPCR) method, and the spread plate method (SPM).

RESULTS

Biofilm formation was significantly induced in 64% of the tested conditions using the CV technique. On the other hand, the qPCR quantifying the total bacterial count and the SPM quantifying the viable bacterial count showed significant induction only in 24% and 17.3%, respectively (Fig. 1). The difference between CV and the other techniques indicates an increase in biofilm biomass without an increase in bacterial growth. As expected, sub-MICs did not reduce the viable cell count, as shown by the SPM. The CV staining method revealed that sub-MICs of imipenem and ciprofloxacin had the highest significance rate (80%) showing an inductive effect on the biofilm development. On the other hand, doxycycline, azithromycin, and gentamicin displayed lower significance rates of 73%, 53%, and 47%, respectively.

CONCLUSION

Exposure to sub-MIC doses of antimicrobial agents induces the biofilm-forming capacity of S. aureus via increasing the total biomass without significantly affecting the bacterial growth of viable count.

Antibacterial and anti-biofilm activities of antibiotic-free phosphatidylglycerol/docosahexaenoic acid lamellar and non-lamellar liquid crystalline nanoparticles

Infectious diseases, particularly those associated with biofilms, are challenging to treat due to an increased tolerance to commonly used antibiotics. This underscores the urgent need for innovative antimicrobial strategies. Here, we present an alternative simple-by-design approach focusing on the development of biocompatible and antibiotic-free nanocarriers from docosahexaenoic acid (DHA) that has the potential to combat microbial infections and phosphatidylglycerol (DOPG), which is attractive for use as a biocompatible prominent amphiphilic component of Gram-positive bacterial cell membranes. We assessed the anti-bacterial and anti-biofilm activities of these nanoformulations (hexosomes and vesicles) against S. aureus and S. epidermidis, which are the most common causes of infections on catheters and medical devices by different methods (including resazurin assay, time-kill assay, and confocal laser scanning microscopy on an in vitro catheter biofilm model). In a DHA-concentration-dependent manner, these nano-self-assemblies demonstrated strong anti-bacterial and anti-biofilm activities, particularly against S. aureus. A five-fold reduction of the planktonic and a four-fold reduction of biofilm populations of S. aureus were observed after treatment with hexosomes. The nanoparticles had a bacteriostatic effect against S. epidermidis planktonic cells but no anti-biofilm activity was detected. We discuss the findings in terms of nanoparticle-bacterial cell interactions, plausible alterations in the phospholipid membrane composition, and potential penetration of DHA into these membranes, leading to changes in their structural and biophysical properties. The implications for the future development of biocompatible nanocarriers for the delivery of DHA alone or in combination with other anti-bacterial agents are discussed, as novel treatment strategies of Gram-positive infections, including biofilm-associated infections.

Characterization of the metabolism of the yeast Yarrowia lipolytica growing as a biofilm

Yarrowia lipolytica is a well-characterized yeast with remarkable metabolic adaptability. It is capable of producing various products from different carbon sources and easily switching between planktonic and biofilm states. A biofilm represents a natural means of cell immobilization that could support continuous cultivation and production processes, such as perfusion cultivation. However, the metabolic activities of Y. lipolytica in biofilms have not yet been studied in detail. Therefore, this study aimed to compare the metabolic activities of Y. lipolytica in biofilm and planktonic states. Conventionally, a stirred tank bioreactor was used to cultivate Y. lipolytica in a planktonic state. On the other hand, a trickle bed bioreactor system was used for biofilm cultivation. The low pH at 3 was maintained to favor polyol production. The accumulation of citric acid was observed over time only in the biofilm state, which significantly differed from the planktonic state. Although the biofilm cultivation process has lower productivity, it has been observed that the production rate remains constant and the total product yield is comparable to the planktonic state when supplied with 42% oxygen-enriched air. This finding indicates that the biofilm state has the potential for continuous bioprocessing applications and is possibly a feasible option.

Unraveling the determinants of antibiotic resistance evolution in farmland under fertilizations

Organic fertilization is a major driver potentiating soil antibiotic resistance in farmland. However, it remains unclear how bacterial antibiotic resistance evolves in fertilized soils and even spreads to crops. Compared with no fertilizer and commercial fertilizer treatments, organic fertilizers markedly increased the abundance of soil antibiotic resistance genes (ARGs) but the relatively weaker transfer of resistance genes from soil to crops. The introduction of organic fertilizers enriches the soil with nutrients, driving indigenous microorganisms towards a K-strategy. The pH, EC, and nutrients as key drivers influenced the ARGs abundance. The neutral (pH 7.2), low salt (TDS 1.4 %) and mesotrophic (carbon content 3.54 g/L) habitats similar to the soil environment conditioned by organic fertilizers. These environmental conditions clearly prolonged the persistence of resistant plasmids, and facilitated their dissemination to massive conjugators soil microbiome but not to plant endophytes. This suggested that organic fertilizers inhibited the spread of ARGs to crops. Moreover, the composition of conjugators showed differential selection of resistant plasmids by endophytes under these conditions. This study sheds light on the evolution and dissemination of antibiotic resistance in farmlands and can aid in the development of antimicrobial resistance control strategies in agriculture.

Spatial Resolution for X-ray Excited Luminescence Chemical Imaging (XELCI)

Measuring chemical concentrations at the surface of implanted medical devices is important for elucidating the local biochemical environment, especially during implant infection. Although chemical indicator dyes enable chemical measurements in vitro, they are usually ineffective when measuring through tissue because the background obscures the dye signal and scattering dramatically reduces the spatial resolution. X-ray excited luminescent chemical imaging (XELCI) is a recent imaging modality which overcomes these limitations using a focused X-ray beam to excite a small spot of red light on scintillator-coated medical implants with well-defined location (because X-rays are minimally scattered) and low background. A spectrochemical indicator film placed over the scintillator layer, e.g., a polymer film containing pH-indicator dyes, absorbs some of the luminescence according to the local chemical environment, and this absorption is then detected by measuring the light intensity/spectrum passing through the tissue. A focused X-ray beam is used to scan point-by-point with a spatial resolution mainly limited by the X-ray beam width with minimum increase from X-ray absorption and scattering in the tissue. X-ray resolution, implant surface specificity, and chemical sensitivity are the three key features of XELCI. Here, we study spatial resolution using optically absorptive targets. For imaging a series of lines, the 20-80% knife-edge resolution was ∼285 (±15) μm with no tissue and 475 ± 18 and 520 ± 34 μm, respectively, through 5 and 10 mm thick tissue. Thus, doubling the tissue depth did not appreciably change the spatial resolution recorded through the tissue. This shows the promise of XELCI for submillimeter chemical imaging through tissue.

Functionalized orthopaedic implant as pH electrochemical sensing tool for smart diagnosis of hardware infection

In the orthopaedic surgery field, the use of medical implants to treat a patient's bone fracture is nowadays a common practice, nevertheless, it is associated with possible cases of infection. The consequent hardware infection can lead to implant failure and systemic infections, with prolonged hospitalization, time-consuming rehabilitation treatments, and extended antibiotic therapy. Hardware infections are strictly related to bacterial adhesion to the implant, leading to infection occurrence and consequent pH decreasing from physiological level to acid pH. Here, we demonstrate the new strategy to use an orthopaedic implant functionalized with iridium oxide film as the working electrode for the potentiometric monitoring of pH in hardware infection diagnosis. A functional investigation was focused on selecting the implant material, namely titanium, titanium alloy, and stainless steel, and the component, namely screws and implants. After selecting the titanium-based implant as the working electrode and a silver wire as the reference electrode in the final configuration of the smart sensing orthopaedic implant, a calibration curve was performed in standard solutions. An equation equal to y = (0.76 ± 0.02) - (0.068 ± 0.002) x, R2 = 0.996, was obtained in the pH range of 4-8. Subsequently, hysteresis, interference, matrix effect, recovery study, and storage stability were investigated to test the overall performance of the sensing device, demonstrating the tremendous potential of electrochemical sensors to deliver the next generation of smart orthopaedic implants.

Recent advances on the formation, detection, resistance mechanism, and control technology of Listeria monocytogenes biofilm in food industry

Listeria monocytogenes is an important foodborne pathogen that causes listeriosis, a severe and fatal condition. Biofilms are communities of microorganisms nested within a self-secreted extracellular polymeric substance, and they protect L. monocytogenes from environmental stresses. Biofilms, once formed, can lead to the persistence of L. monocytogenes in processing equipment and are therefore considered to be a major concern for the food industry. This paper briefly introduces the recent advancements on biofilm formation characteristics and detection methods, and focuses on analysis of the mechanism of L. monocytogenes biofilm resistance; Moreover, this paper also summarizes and discusses the existing different techniques of L. monocytogenes biofilm control according to the physical, chemical, biological, and combined strategies, to provide a theoretical reference to aid the choice of effective control technology in the food industry.

Etiology, pathology, and host-impaired immunity in medical implant-associated infections

Host impaired immunity and pathogens adhesion factors are the key elements in analyzing medical implant-associated infections (MIAI). The infection chances are further influenced by surface properties of implants. This review addresses the medical implant-associated pathogens and summarizes the etiology, pathology, and host-impaired immunity in MIAI. Several bacterial and fungal pathogens have been isolated from MIAI; together, they form cross-kingdom species biofilms and support each other in different ways. The adhesion factors initiate the pathogen's adherence on the implant's surface; however, implant-induced impaired immunity promotes the pathogen's colonization and biofilm formation. Depending on the implant's surface properties, immune cell functions get slow or get exaggerated and cause immunity-induced secondary complications resulting in resistant depression and immuno-incompetent fibro-inflammatory zone that compromise implant's performance. Such consequences lead to the unavoidable and straightforward conclusion for the downstream transformation of new ideas, such as the development of multifunctional implant coatings.

A growing battlefield in the war against biofilm-induced antimicrobial resistance: insights from reviews on antibiotic resistance

Biofilms are a common survival strategy employed by bacteria in healthcare settings, which enhances their resistance to antimicrobial and biocidal agents making infections difficult to treat. Mechanisms of biofilm-induced antimicrobial resistance involve reduced penetration of antimicrobial agents, increased expression of efflux pumps, altered microbial physiology, and genetic changes in the bacterial population. Factors contributing to the formation of biofilms include nutrient availability, temperature, pH, surface properties, and microbial interactions. Biofilm-associated infections can have serious consequences for patient outcomes, and standard antimicrobial therapies are often ineffective against biofilm-associated bacteria, making diagnosis and treatment challenging. Novel strategies, including antibiotics combination therapies (such as daptomycin and vancomycin, colistin and azithromycin), biofilm-targeted agents (such as small molecules (LP3134, LP3145, LP4010, LP1062) target c-di-GMP), and immunomodulatory therapies (such as the anti-PcrV IgY antibodies which target Type IIIsecretion system), are being developed to combat biofilm-induced antimicrobial resistance. A multifaceted approach to diagnosis, treatment, and prevention is necessary to address this emerging problem in healthcare settings.

Resistance development in Escherichia coli to delafloxacin at pHs 6.0 and 7.3 compared to ciprofloxacin

Understanding the resistance mechanisms of antibiotics in the micro-environment of the infection is important to assess their clinical applicability and potentially prevent resistance development. We compared the laboratory resistance evolution of Escherichia coli to delafloxacin (DLX) compared to ciprofloxacin (CIP), the co-resistance evolution, and underlying resistance mechanisms at different pHs. Three clones from each of the eight clinical E. coli isolates were subjected to subinhibitory concentrations of DLX or CIP in parallel at either pH 7.3 or 6.0. Minimum inhibitory concentrations (MICs) were regularly tested (at respective pHs), and the antibiotic concentration was adjusted accordingly. After 30 passages, MICs were determined in the presence of the efflux pump inhibitor phenylalanine-arginine-β-naphthylamide. Whole genome sequencing of the parental isolates and their resistant derivatives (n = 54) was performed. Complementation assays were carried out for selected mutations. Quantitative PCR and efflux experiments were carried out for selected derivatives. For DLX-challenged strains, resistance to DLX evolved much slower in acidic than in neutral pH, whereas for CIP-challenged strains, the opposite was the case. Mutations in the quinolone resistance-determining region were mainly seen in CIP-challenged E. coli, whereas a multifactorial mechanism including mutations in efflux-related genes played a role in DLX resistance evolution (predominantly at pH 6.0). This work provides novel insights into the resistance mechanisms of E. coli to delafloxacin and highlights the importance of understanding micro-environmental conditions at the infection site that might affect the true clinical efficacy of antibiotics and challenges our current antibiotic susceptibility-testing paradigm.

Polymyxin B stabilized DNA micelles for sustained antibacterial and antibiofilm activity against P. aeruginosa

Nucleic acid-based materials showcase an increasing potential for antimicrobial drug delivery. Although numerous reports on drug-loaded DNA nanoparticles outline their pivotal antibacterial activities, their potential as drug delivery systems against bacterial biofilms awaits further studies. Among different oligonucleotide structures, micellar nanocarriers derived from amphiphilic DNA strands are of particular interest due to their spontaneous self-assembly and high biocompatibility. However, their clinical use is hampered by structural instability upon cation depletion. In this work, we used a cationic amphiphilic antibiotic (polymyxin B) to stabilize DNA micelles destined to penetrate P. aeruginosa biofilms and exhibit antibacterial/antibiofilm properties. Our study highlights how the strong affinity of this antibiotic enhances the stability of the micelles and confirms that antibacterial activity of the novel micelles remains intact. Additionally, we show that PMB micelles can penetrate P. aeruginosa biofilms and impact their metabolic activity. Finally, PMB micelles were highly safe and biocompatible, highlighting their possible application against P. aeruginosa biofilm-colonized skin wounds.

Horizontal Gene Transfer of Antibiotic Resistance Genes in Biofilms

Most bacteria attach to biotic or abiotic surfaces and are embedded in a complex matrix which is known as biofilm. Biofilm formation is especially worrisome in clinical settings as it hinders the treatment of infections with antibiotics due to the facilitated acquisition of antibiotic resistance genes (ARGs). Environmental settings are now considered as pivotal for driving biofilm formation, biofilm-mediated antibiotic resistance development and dissemination. Several studies have demonstrated that environmental biofilms can be hotspots for the dissemination of ARGs. These genes can be encoded on mobile genetic elements (MGEs) such as conjugative and mobilizable plasmids or integrative and conjugative elements (ICEs). ARGs can be rapidly transferred through horizontal gene transfer (HGT) which has been shown to occur more frequently in biofilms than in planktonic cultures. Biofilm models are promising tools to mimic natural biofilms to study the dissemination of ARGs via HGT. This review summarizes the state-of-the-art of biofilm studies and the techniques that visualize the three main HGT mechanisms in biofilms: transformation, transduction, and conjugation.