Simultaneous ultrasound-assisted hybrid polyzwitterion/antimicrobial peptide nanoparticles synthesis and deposition on silicone urinary catheters for prevention of biofilm-associated infections

Nosocomial infections caused by antibiotic-resistant bacteria are constantly growing healthcare threats, as they are the reason for the increased mortality, morbidity, and considerable financial burden due to the poor infection outcomes. Indwelling medical devices, such as urinary catheters, are frequently colonized by bacteria in the form of biofilms that cause dysfunction of the device and severe chronic infections. The current treatment strategies of such device-associated infections are impaired by the resistant pathogens but also by a risk of prompting the appearance of new antibiotic-resistant bacterial mechanisms. Herein, the one-step sonochemical synthesis of hybrid poly(sulfobetaine) methacrylate/Polymyxin B nanoparticles (pSBMA@PM NPs) coating was employed to engineer novel nanoenabled silicone catheters with improved antifouling, antibacterial, and antibiofilm efficiencies. The synergistic mode of action of nanohybridized zwitterionic polymer and antimicrobial peptide led to complete inhibition of the nonspecific protein adsorption and up to 97% reduction in Pseudomonas aeruginosa biofilm formation, in comparison with the pristine silicone. Additionally, the bactericidal activity in the hybrid coating reduced the free-floating and surface-attached bacterial growth by 8 logs, minimizing the probability for further P. aeruginosa spreading and host invasion. This coating was stable for up to 7 days under conditions simulating the real scenario of catheter usage and inhibited by 80% P. aeruginosa biofilms. For the same time of use, the pSBMA@PM NPs coating did not affect the metabolic activity and morphology of mammalian cells, demonstrating their capacity to control antibiotic-resistant biofilm-associated bacterial infections.Peer ReviewedPostprint (published version

Nanostructured coatings for controlling bacterial biofilms and antibiotic resistance

The accelerated emergence of drug resistant bacteria is one of the most serious problems in healthcare and the difficulties in finding new antibiotics make it even more challenging. To overcome the action of antibiotics bacteria develop effective resistance mechanisms including the formation of biofilms. Biofilms are bacterial communities of cells embedded in a self-produced polymeric matrix commonly found on medical devices such as indwelling catheters. When pathogens adopt this mode of growth on the surface, they effectively circumvent host immune defences and antibiotic therapy, causing severe and life threatening infections. This thesis focuses on the development of advanced nanoscale materials and coatings for controlling bacterial biofilms and the emergence of drug resistance. To this end, acylase and amylase enzymes degrading essential for the biofilm growth components, were innovatively combined into hybrid nanocoatings to impart antibiofilm functionalities onto indwelling medical devices. Alternatively, ultrasound-assisted nanotransformation of antimicrobials was used as a tool for enhancing their antibacterial efficacy and overcoming the intrinsic drug resistant mechanisms in Gram-negative bacteria. These strategies offer new perspectives for prevention and treatment of biofilm infections, limiting the selection and spread of antibiotic resistance. The first part of the thesis describes the building of enzyme multilayer coatings able to interfere with bacterial quorum sensing (QS) and prevent biofilm establishment on silicone urinary catheters. This was achieved by alternate deposition of negatively charged acylase and oppositely charged polyethylenimine in a Layer-by-Layer (LbL) fashion. The acylase-coated catheters degraded bacterial signalling molecules and inhibited the QS process of Gram-negative bacteria. These coatings also significantly reduced the biofilm growth on urinary catheters under conditions mimicking the real situation in catheterised patients, without affecting the human cells viability. Acylase was further combined with the matrix degrading amylase enzyme into hybrid multilayer coatings able to interfere simultaneously with bacterial QS signals and biofilm integrity. The LbL assembly of both enzymes into hybrid nanocoatings resulted in stronger biofilm inhibition as a function of acylase or amylase location in the multi-layer coating. Hybrid nanocoatings with the QS inhibiting acylase as outermost layer reduced the occurrence of single and multi-species biofilms on silicone catheters in vitro and in an in vivo animal model. The thesis also reports on the efficacy of nanomaterials for prevention and eradication of antibiotic resistant biofilms. Multilayer assemblies that contain in their structure and release on demand antibacterial polycationic nanospheres (NSs) were engineered on silicone surfaces. A polycationic aminocellulose (AC) conjugate was first transformed into NSs with enhanced bactericidal activity and then combined with hyaluronic acid to build bacteria-responsive layers on silicone material. When challenged with bacteria these multilayers disassembled gradually inhibiting both planktonic and biofilm modes of bacterial growth. The same AC NSs were also covalently immobilised on silicone material using epoxy-amine conjugation chemistry. The intact NSs on the silicone material were able to inhibit bacterial biofilm growth, suggesting the potential of epoxy-amine curing reaction for generation of stable non-leaching coatings on silicone-based medical devices. Finally, ultrasound-assisted nanotransformation of penicillin G was used as a strategy to boost its activity towards bacteria. The efficient penetration of the NSs within a biomimetic membranes sustained the theory that they may reach the periplasmic space in Gram-negative bacteria and exert their bactericidal activity "unrecognised" as a threat by bacteria for selection of resistance.La rápida aparición de bacterias resistentes a fármacos es uno de los problemas más graves del sistema sanitario convirtiéndose en un gran reto encontrar nuevos antibióticos. Para superar la acción de los antibióticos, las bacterias utilizan diferentes mecanismos de resistencia incluyendo la formación de biopelículas. Las biopelículas son comunidades complejas de células bacterianas unidas por una matriz polimérica comúnmente encontradas en dispositivos médicos invasivos como los catéteres urinarios. Cuando los patógenos adoptan este modo de crecimiento en superficies, evitan eficazmente las defensas inmunitarias y el efecto de los antibióticos, causando infecciones. Esta tesis se centra en el desarrollo de nuevos materiales y recubrimientos nanoestructurados para el control de biopelículas bacterianas y la reducción de su resistencia a antibióticos. Por lo tanto, las enzimas acilasa y amilasa, capaces de degradar los componentes necesarios de las bacterias para formar biopelículas, se combinaron de forma innovadora en nanorecubrimientos híbridos para intervenir en el crecimiento de las biopelículas en dispositivos médicos permanentes. Además, la transformación de agentes antimicrobianos a forma "nano" se utilizó para mejorar su eficacia antibacteriana y superarlos mecanismos de resistencia a fármacos de las bacterias. Estas estrategias ofrecen nuevas perspectivas para el tratamiento de las infecciones relacionadas con biopelículas, limitando la selección y propagación de la resistencia bacteriana. La primera parte de la tesis describe la generación de recubrimientos multicapa de enzimas capaces de interferir con el sistema de comunicación bacteriana, denominado quórum sensing (QS) y prevenir la formación de biopelículas en el superficie de los catéteres urinarios. Esto se consiguió por deposición alternada de acilasa, cargada negativamente, y polietilenimina, cargada de manera opuesta, en la forma de capa a capa (LbL). Los catéteres recubiertos con acilasa inhibieron el proceso QS de bacterias Gram-negativas y redujeron significativamente el crecimiento de biopelículas en los catéteres urinarios en condiciones que imitaban la situación real en pacientes cateterizados. Adicionalmente, la acilasa se combinó con la enzima amilasa en recubrimientos híbridos capaces de interferir con las señales de comunicación entre bacterias y la integridad de la matriz de la biopelícula. El ensamblaje de las dos enzimas en recubrimientos híbridos dio lugar a una inhibición de la formación de biopelículas más fuerte en función de la localización de la acilasa o de la amilasa en la multicapa. Nanorecubrimientos con acilasa en la capa más externa redujo la formación de biopelículas en catéteres de silicona in vitro y en un modelo animal in vivo. La tesis también muestra la eficacia de nanomateriales para el control de biopelículas bacterianas. Las nanoesferas (NSs) antibacterianas, que contienen en su estructura multicapas ensambladas que se liberan bajo demanda, fueron depositados sobre silicona. Aminocelulosa (AC) se transformó primero en NSs obteniendo una mejor actividad bactericida y luego se combinó con ácido hialurónico para construir capas sensibles a las bacterias. Cuando se ponen en contacto con bacterias, estas capas se desmontan gradualmente inhibiendo las formas planctónicas y biopelículas. Los mismos ACNS también se inmovilizaron sobre silicona usando epoxi-amina. Las NSs intactas fueron capaces de inhibir el crecimiento de la biopelícula, lo que demuestra el potencial de la reacción de epoxi-amina para la generación de recubrimientos estables en dispositivos médicos de silicona. Finalmente, la nanotransformación de la penicilina G se utilizó como otra estrategia para aumentar la actividad del antibiótico hacia bacterias. Se demostró la a penetración efectiva de las partículas dentro de membrananas biomimeticas sugiera que las partículas alcanzan el espacio periplásmico en las bacterias y ejercen su actividad bactericida.Postprint (published version

Strategies to prevent the occurrence of resistance against antibiotics by using advanced materials

This is a post-peer-review, pre-copyedit version of an article published in Applied microbiology and biotechnology The final authenticated version is available online at: http://dx.doi.org/10.1007/s00253-018-8776-0Drug resistance occurrence is a global healthcare concern responsible for the increased morbidity and mortality in hospitals, time of hospitalisation and huge financial loss. The failure of the most antibiotics to kill Bsuperbugs^ poses the urgent need to develop innovative strategies aimed at not only controlling bacterial infection but also the spread of resistance. The prevention of pathogen host invasion by inhibiting bacterial virulence and biofilm formation, and the utilisation of bactericidal agents with different mode of action than classic antibiotics are the two most promising new alternative strategies to overcome antibiotic resistance. Based on these novel approaches, researchers are developing different advanced materials (nanoparticles, hydrogels and surface coatings) with novel antimicrobial properties. In this review, we summarise the recent advances in terms of engineered materials to prevent bacteria-resistant infections according to the antimicrobial strategies underlying their design.Peer ReviewedPostprint (author's final draft

Layer-by-Layer coating of aminocellulose and quorum quenching acylase on silver nanoparticles synergistically eradicate bacteria and their biofilms

The emergence of antibiotic-resistant bacteria and the failure of the existing antibacterial therapeutics call for development of novel treatment strategies. Furthermore, the formation of bacterial biofilms restricts drug penetration and efficiency, causing life-threatening infections. Bacterial attachment and biofilm formation are regulated by the cell-to-cell communication phenomenon called quorum sensing (QS). In this work, antimicrobial silver nanoparticles (AgNPs) are decorated in a layer-by-layer fashion with the oppositely charged aminocellulose (AM) and acylase to generate hybrid nanoentities with enhanced antibacterial and antibiofilm activities as well as reduced cytotoxicity. Acylase, a quorum-quenching enzyme that degrades the QS signals in the extracellular environment of bacteria, disrupts the bacterial QS process and together with the bactericidal AM synergistically lowers fourfold the minimum inhibitory concentration of the AgNPs templates toward Gram-negative Pseudomonas aeruginosa (P. aeruginosa). The hybrid nanoparticles in eightfold-lower concentration than the AgNPs inhibit 45% of the QS-regulated virulence factors produced by the reporter Chromobacterium violaceum bacterial strain and reduce by 100% the P. aeruginosa biofilm formation. Moreover, the sequential deposition of antibacterial/antibiofilm active and biocompatible biopolymers onto the AgNPs allows the engineering of safe nanomaterials that do not affect the viability of human cells.Peer ReviewedPostprint (published version

Immobilization of antimicrobial core-shell nanospheres onto silicone for prevention of Escherichia coli biofilm formation

Escherichia coli (E. coli) strains are among the most frequently isolated microorganisms in urinary tract infections able to colonize the surface of urinary catheters and form biofilms. These biofilms are highly resistant to antibiotics and host immune system, resulting in increased morbidity and mortality rates. Strategies to prevent biofilm development, especially via restricting the initial stages of bacteria attachment are therefore urgently needed. Herein, a common urinary catheter material – polydimethylsiloxane (PDMS) – was covalently functionalized with antibacterial aminocellulose nanospheres (ACNSs) using the epoxy/amine grafting chemistry. The PDMS surface was pre-activated with (3-glycidyloxypropyl)-triethoxysilane to introduce epoxy functionalities prior to immobilization of the intact ACNSs via its amino groups. The AC biopolymer was first sonochemically processed into NSs improving by up to 80% its potential to prevent the E. coli biofilm formation on a polystyrene surface. The silicone surface decorated with these NSs demonstrated efficient inhibition of E. coli biofilms, reducing the total biomass when compared with pristine silicone material. Therefore, the functionalization of silicone-based materials with ACNSs shows promise as potential platform for prevention of biofilm-associated infections caused by E. coli.Peer ReviewedPostprint (author's final draft

Nano-formulation endows quorum quenching enzyme-antibiotic hybrids with improved antibacterial and antibiofilm activities against pseudomonas aeruginosa

The emergence of antibiotic resistant bacteria coupled with the shortage of efficient antibacterials is one of the most serious unresolved problems for modern medicine. In this study, the nano-hybridization of the clinically relevant antibiotic, gentamicin, with the bacterial pro-pathological cell-to-cell communication-quenching enzyme, acylase, is innovatively employed to increase its antimicrobial efficiency against Pseudomonas aeruginosa planktonic cells and biofilms. The sonochemically generated hybrid gentamicin/acylase nano-spheres (GeN_AC NSs) showed a 16-fold improved bactericidal activity when compared with the antibiotic in bulk form, due to the enhanced physical interaction and disruption of the P. aeruginosa cell membrane. The nano-hybrids attenuated 97 ± 1.8% of the quorum sensing-regulated virulence factors’ production and inhibited the bacterium biofilm formation in an eight-fold lower concentration than the stand-alone gentamicin NSs. The P. aeruginosa sensitivity to GeN_AC NSs was also confirmed in a real time assay monitoring the bacterial cells elimination, using a quartz crystal microbalance with dissipation. In protein-enriched conditions mimicking the in vivo application, these hybrid nano-antibacterials maintained their antibacterial and antibiofilm effectiveness at concentrations innocuous to human cells. Therefore, the novel GeN_AC NSs with complementary modes of action show potential for the treatment of P. aeruginosa biofilm infections at a reduced antibiotic dosage.Peer ReviewedPostprint (published version

Nanotransformation of vancomycin overcomes the intrinsic resistance of Gram-negative bacteria

The increased emergence of antibiotic-resistant bacteria is a growing public health concern, and although new drugs are constantly being sought, the pace of development is slow compared with the evolution and spread of multidrug- resistant species. In this study, we developed a novel broad-spectrum antimicrobial agent by simply transforming vancomycin into nanoform using sonochemistry. Vancomycin is a glycopeptide antibiotic largely used for the treatment of infections caused by Gram-positive bacteria but inefficient against Gram-negative species. The nanospherization extended its effect toward Gram-negative Escherichia coli and Pseudomonas aeruginosa, making these bacteria up to 10 and 100 times more sensitive to the antibiotic, respectively. The spheres were able to disrupt the outer membranes of these bacteria, overcoming their intrinsic resistance toward glycopeptides. The penetration of nanospheres into a Langmuir monolayer of bacterial membrane phospholipids confirmed the interaction of the nanoantibiotic with the membrane of E. coli cells, affecting their physical integrity, as further visualized by scanning electron microscopy. Such mechanism of antibacterial action is unlikely to induce mutations in the evolutionary conserved bacterial membrane, therefore reducing the possibility of acquiring resistance. Our results indicated that the nanotransformation of vancomycin could overcome the inherent resistance of Gram-negative bacteria toward this antibiotic and disrupt mature biofilms at antibacterial-effective concentrations.Peer ReviewedPostprint (author's final draft

Multimodal silver-chitosan-acylase nanoparticles inhibit bacterial growth and biofilm formation by gram-negative pseudomonas aeruginosa bacterium

Pseudomonas aeruginosa bacteria originate severe infections in hospitalized patients and those with chronic debilitating diseases leading to increased morbidity and mortality, longer hospitalization and huge financial burden to the healthcare system. The clinical relevance of P. aeruginosa infections is increased by the capability of this bacterium to grow in biofilms and develop multidrug resistant mechanisms that preclude conventional antibiotic treatments. Herein, we engineered novel multimodal nanocomposites that integrate in the same entity antimicrobial silver nanoparticles (NPs), the intrinsically antimicrobial, but biocompatible biopolymer chitosan, and the anti-infective quorum quenching enzyme acylase I. Acylase present in the NPs specifically degraded the signal molecules governing bacterial cell-to-cell communication and inhibited by ~55 % P. aeruginosa biofilm formation, while the silver/chitosan template altered the integrity of bacterial membrane, leading to complete eradication of planktonic bacteria. The innovative combination of multiple bacteria targeting modalities resulted in 100-fold synergistic enhancement of the antimicrobial efficacy of the nanocomposite at lower and non-hazardous towards human skin cells concentrations, compared to the silver/chitosan NPs alone.Peer ReviewedPostprint (published version

Multifunctional ZnO NPs-chitosan-gallic acid hybrid nanocoating to overcome contact lenses associated conditions and discomfort

Contact lenses (CL) provide visual correction but their use may also induce several adverse effects causative of discomfort and conditions that lead to stop or discontinue their use. Discomfort is mainly caused by insufficient wetting, impairment of the antioxidant defence system and eye infections. The current work reports on a single step sonochemical coating of CL with ZnO nanoparticles (NPs), chitosan (CS) and gallic acid (GA). GA and CS are expected to improve the comfort of CL by imparting respectively antioxidant properties and enhanced wettability, while their combination with ZnO NPs provides the CL with antimicrobial properties. The ternary composite coating presents high antibacterial efficiency (> 4.5 logs reduction) against S. aureus causative of CL-related conditions, and maintains good biocompatibility (> 72 %) with human cell lines. The obtained multi-functionality on the CL did not affect their geometry and refractive properties.Peer ReviewedPostprint (author's final draft

Interaction of silver-lignin nanoparticles with mammalian mimetic membranes

Silver nanoparticles (AgNPs) have broad spectrum antibacterial activity, but their toxicity to human cells has raised concerns related to their use as disinfectants or coatings of medically relevant surfaces. To address this issue, NPs comprising intrinsically bactericidal and biocompatible biopolymer and Ag with high antibacterial efficacy against common pathogens and compatibility to human cells have been engineered. However, the reason for their lower toxicity compared to AgNPs has not yet been elucidated. This work studies the in vitro interaction of AgLNPs with model mammalian membranes through two approaches: (i) Langmuir films and (ii) supported planar bilayers studied by quartz crystal microbalance and atomic force spectroscopy. These approaches elucidate the interactions of AgLNPs with the model membranes indicating a prominent effect of the bioresourced lignin to facilitate the binding of AgLNPs to the mammalian membrane, without penetrating through it. This study opens a new avenue for engineering of hybrid antimicrobial biopolymer – Ag or other metal NPs with improved bactericidal effect whereas maintaining good biocompatibilityPeer ReviewedPostprint (published version