Controlled drug delivery systems in eradicating bacterial biofilm-associated infections

Drug delivery systems (DDS) have extensively progressed over the past decades for eradicating the bacteria embedded in biofilms while minimizing the side effects of antimicrobials on the normal tissues. They possess potential in solving the challenges of intrinsic antimicrobial-resistance and poor penetration of antimicrobials into biofilms. However, the guidelines for developing a controlled DDS for combating bacterial biofilms are limited. In this review, classical mechanisms and mathematical models of DDS were summarized in order to lay the foundation of controlled DDS development. Strategies for building controlled DDS were proposed based on the process of biofilm formation, including surface coatings, fibers, nanoparticles as DDS to prevent biofilm formation and eradicate bacterial biofilm-associated infections. The challenges that still remain in DDS design were discussed and future directions were suggested. We hope this review could give a "road map" to inspire readers and boost the development of the new generation of controlled drug release system for antimicrobial applications

Recent advances and future challenges in the use of nanoparticles for the dispersal of infectious biofilms

Increasing occurrence of intrinsically antimicrobial-resistant, human pathogens and the protective biofilm-mode in which they grow, dictates a need for the alternative control of infectious biofilms. Biofilm bacteria utilize dispersal mechanisms to detach parts of a biofilm as part of the biofilm life-cycle during times of nutrient scarcity or overpopulation. We here identify recent advances and future challenges in the development of dispersants as a new infection-control strategy. Deoxyribonuclease (DNase) and other extracellular enzymes can disrupt the extracellular matrix of a biofilm to cause dispersal. Also, a variety of small molecules, reactive oxygen species, nitric oxide releasing compounds, peptides and molecules regulating signaling pathways in biofilms have been described as dispersants. On their own, dispersants do not inhibit bacterial growth or kill bacterial pathogens. Both natural, as well as artificial dispersants, are unstable and hydrophobic which necessitate their encapsulation in smart nanocarriers, like pH-responsive micelles, liposomes or hydrogels. Depending on their composition, nanoparticles can also possess intrinsic dispersant properties. Bacteria dispersed from an infectious biofilm end up in the blood circulation where they are cleared by host immune cells. However, this sudden increase in bacterial concentration can also cause sepsis. Simultaneous antibiotic loading of nanoparticles with dispersant properties or combined administration of dispersants and antibiotics can counter this threat. Importantly, biofilm remaining after dispersant administration appears more susceptible to existing antibiotics. Being part of the natural biofilm life-cycle, no signs of "dispersant-resistance" have been observed. Dispersants are therewith promising for the control of infectious biofilms. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Lipid-Based Antimicrobial Delivery-Systems for the Treatment of Bacterial Infections

Many nanotechnology-based antimicrobials and antimicrobial-delivery-systems have been developed over the past decades with the aim to provide alternatives to antibiotic treatment of infectious-biofilms across the human body. Antimicrobials can be loaded into nanocarriers to protect them against de-activation, and to reduce their toxicity and potential, harmful side-effects. Moreover, antimicrobial nanocarriers such as micelles, can be equipped with stealth and pH-responsive features that allow self-targeting and accumulation in infectious-biofilms at high concentrations. Micellar and liposomal nanocarriers differ in hydrophilicity of their outer-surface and inner-core. Micelles are self-assembled, spherical core-shell structures composed of single layers of surfactants, with hydrophilic head-groups and hydrophobic tail-groups pointing to the micellar core. Liposomes are composed of lipids, self-assembled into bilayers. The hydrophilic head of the lipids determines the surface properties of liposomes, while the hydrophobic tail, internal to the bilayer, determines the fluidity of liposomal-membranes. Therefore, whereas micelles can only be loaded with hydrophobic antimicrobials, hydrophilic antimicrobials can be encapsulated in the hydrophilic, aqueous core of liposomes and hydrophobic or amphiphilic antimicrobials can be inserted in the phospholipid bilayer. Nanotechnology-derived liposomes can be prepared with diameter

Synergy between "Probiotic" Carbon Quantum Dots and Ciprofloxacin in Eradicating Infectious Biofilms and Their Biosafety in Mice

Orally administrated probiotic bacteria can aid antibiotic treatment of intestinal infections, but their arrival at their intestinal target site is hampered by killing in the gastrointestinal tract and by antibiotics solely intended for pathogen killing. Carbon-quantum-dots are extremely small nanoparticles and can be derived from different sources, including bacteria. Here, we hypothesize that carbon-quantum-dots inherit antibacterial activity from probiotic source bacteria to fulfill a similar role as live probiotics in intestinal infection therapy. Physico-chemical analyses indicated that carbon-quantum-dots, hydrothermally derived from Bifidobacterium breve (B-C-dots), inherited proteins and polysaccharides from their source-bacteria. B-C-dots disrupted biofilm matrices of Escherichia coli and Salmonella typhimurium biofilms through extensive reactive-oxygen-species (ROS)-generation, causing a decrease in volumetric bacterial-density in biofilms. Decreased bacterial densities leave more open space in biofilms and have enhanced ciprofloxacin penetration and killing potential in an E. coli biofilm pre-exposed to probiotic B-C-dots. Pathogenic carbon-quantum-dots hydrothermally derived from E. coli (E-C-dots) did not disrupt pathogenic biofilms nor enhance E. coli killing potential by ciprofloxacin. B-C-dots were biosafe in mice upon daily administration, while E-C-dots demonstrated a decrease in white blood cell and platelet counts and an increase in C-reactive protein levels. Therefore, the way is paved for employing probiotic carbon-quantum-dots instead of viable, probiotic bacteria for synergistic use with existing antibiotics in treating intestinal infections

Applications and Perspectives of Cascade Reactions in Bacterial Infection Control

Cascade reactions integrate two or more reactions, of which each subsequent reaction can only start when the previous reaction step is completed. Employing natural substrates in the human body such as glucose and oxygen, cascade reactions can generate reactive oxygen species (ROS) to kill tumor cells, but cascade reactions may also have potential as a direly needed, novel bacterial infection-control strategy. ROS can disintegrate the EPS matrix of infectious biofilm, disrupt bacterial cell membranes, and damage intra-cellular DNA. Application of cascade reactions producing ROS as a new infection-control strategy is still in its infancy. The main advantages for infection-control cascade reactions include the fact that they are non-antibiotic based and induction of ROS resistance is unlikely. However, the amount of ROS generated is generally low and antimicrobial efficacies reported are still far <3-4 log units necessary for clinical efficacy. Increasing the amounts of ROS generated by adding more substrate bears the risk of collateral damage to tissue surrounding an infection site. Collateral tissue damage upon increasing substrate concentrations may be prevented by locally increasing substrate concentrations, for instance, using smart nanocarriers. Smart, pH-responsive nanocarriers can self-target and accumulate in infectious biofilms from the blood circulation to confine ROS production inside the biofilm to yield long-term presence of ROS, despite the short lifetime (nanoseconds) of individual ROS molecules. Increasing bacterial killing efficacies using cascade reaction components containing nanocarriers constitutes a first, major challenge in the development of infection-control cascade reactions. Nevertheless, their use in combination with clinical antibiotic treatment may already yield synergistic effects, but this remains to be established for cascade reactions. Furthermore, specific patient groups possessing elevated levels of endogenous substrate (for instance, diabetic or cancer patients) may benefit from the use of cascade reaction components containing nanocarriers

Liposomes with Water as a pH-Responsive Functionality for Targeting of Acidic Tumor and Infection Sites

A lipid named DCPA was synthesized under microwave-assisted heating. DCPA possesses a pyridine betaine, hydrophilic group that can be complexed with water through hydrogen bonding (DCPA-H2O). DCPA-H2O liposomes became protonated relatively fast already at p

Accepting higher morbidity in exchange for sacrificing fewer animals in studies developing novel infection-control strategies.

Preventing bacterial infections from becoming the leading cause of death by the year 2050 requires the development of novel, infection-control strategies, building heavily on biomaterials science, including nanotechnology. Pre-clinical (animal) studies are indispensable for this development. Often, animal infection outcomes bear little relation to human clinical outcome. Here, we review conclusions from pathogen-inoculum dose-finding pilot studies for evaluation of novel infection-control strategies in murine models. Pathogen-inoculum doses are generally preferred that produce the largest differences in quantitative infection outcome parameters between a control and an experimental group, without death or termination of animals due to having reached an inhumane end-point during the study. However, animal death may represent a better end-point for evaluation than large differences in outcome parameters or number of days over which infection persists. The clinical relevance of lower pre-clinical outcomes, such as bioluminescence, colony forming units (CFUs) retrieved or more rapid clearance of infection is unknown, as most animals cure infection without intervention, depending on pathogen-species and pathogen-inoculum dose administered. In human clinical practice, patients suffering from infection present to hospital emergency wards, frequently in life-threatening conditions. Animal infection-models should therefore use prevention of death and recurrence of infection as primary efficacy targets to be addressed by novel strategies. To compensate for increased animal morbidity and mortality, animal experiments should solely be conducted for pre-clinical proof of principle and safety. With the advent of sophisticated in vitro models, we advocate limiting use of animal models when exploring pathogenesis or infection mechanisms

Protection of DNase in the shell of a pH-responsive, antibiotic-loaded micelle for biofilm targeting, dispersal and eradication

DNase can break down the extracellular matrix that keeps infectious bacterial biofilm together through cleavage of eDNA. Herewith, biofilm bacteria can become dispersed to assist antibiotic eradication but this has hitherto remained an in vitro possibility. In vivo DNase is rapidly broken down in blood, impeding blood-injection of DNase combined with antibiotics to cure bacterial infections. Herein, we report the synthesis of pH-responsive, self-targeting micelles self-assembled from a solution of poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) and poly(ε-caprolactone)-block-poly(amino ester) (PCL-b-PAE) with DNase conjugated to PAE-blocks. At physiological pH, this conjugation protected DNase inside the micellar shell, while PEG prevented adsorption of blood-borne proteins to the micelles. PAE became positively-charged below pH 6.4 facilitating self-targeting to an infectious biofilm. Simultaneously, PAE became hydrophilic and stretched to expose DNase upon accumulation in an infectious S. aureus biofilm where it degraded the biofilm matrix. PEG/PAE-DNase micelles internally core-loaded with ciprofloxacin significantly better eradicated murine pneumonia after blood-injection than ciprofloxacin-loaded PEG/PAE micelles without conjugated DNase or ciprofloxacin free in solution. Considering that DNase is clinically approved for use in cystic fibrosis patients, this paves the way for clinical translation of ciprofloxacin-loaded, PEG/PAE-DNase micelles for the treatment of pneumonia and other infections that can be reached through self-targeting after blood-injection

Proton-mediated burst of dual-drug loaded liposomes for biofilm dispersal and bacterial killing

Exposure of infectious biofilms to dispersants induces high bacterial concentrations in blood that may cause sepsis. Preventing sepsis requires simultaneous biofilm dispersal and bacterial killing. Here, self-targeting DCPA(2-(4-((1,5-bis(octadecenoyl)1,5-dioxopentan-2-yl)carbamoyl)pyridin-1-ium-1-yl)acetate) liposomes with complexed water were self-assembled with ciprofloxacin loaded in-membrane and PEGylated as a lipid-membrane component, together with bromelain loaded in-core. Inside biofilms, DCPA-H2O and PEGylated ciprofloxacin became protonated, disturbing the balance in the lipid-membrane to cause liposome-burst and simultaneous release of bromelain and ciprofloxacin. Simultaneous release of bromelain and ciprofloxacin enhanced bacterial killing in Staphylococcus aureus biofilms as compared with free bromelain and/or ciprofloxacin. After tail-vein injection in mice, liposomes accumulated inside intra-abdominal staphylococcal biofilms. Subsequent liposome-burst and simultaneous release of bromelain and ciprofloxacin yielded degradation of the biofilm matrix by bromelain and higher bacterial killing without inducing septic symptoms as obtained by injection of free bromelain and ciprofloxacin. This shows the advantage of simultaneous release from liposomes of bromelain and ciprofloxacin inside a biofilm