An overview of the methodological approach to the in vitro study of anti-infective biomaterials

S. aureus develops biofilms on titanium within 2 weeks in vitro

BACKGROUND

The formation of biofilms, characterized by cell aggregation and extracellular polymeric substance (EPS) production, is a common feature of periprosthetic joint infections (PJI).

OBJECTIVE

The current study aimed to investigate the development of biofilm features in vitro within less than 3 weeks by Staphylococcus aureus isolated from PJIs.

METHODS

Biofilms were grown on sandblasted titanium discs, and fluorescence spectroscopy and microscopy were used to observe biofilm maturation for 21 days.

RESULTS

DNA mass decreased initially, then increased from day 5 onwards, and decreased again after day 7. The proportion of living to dead bacteria oscillated until day 7 and increased at day 10 for strain A and day 14 for strain B. EPS mass decreased initially and then continuously increased. Multilayer bacterial organization was observed at day 7.

CONCLUSION

Cell aggregation occurred during the first week, followed by EPS production in the second week, and characteristic biofilm features were observed within 1 to 2 weeks.

Extracellular DNA (eDNA). A Major Ubiquitous Element of the Bacterial Biofilm Architecture

After the first ancient studies on microbial slime (the name by which the biofilm matrix was initially indicated), multitudes of studies on the morphology, composition and physiology of biofilms have arisen. The emergence of the role that biofilms play in the pathogenesis of recalcitrant and persistent clinical infections, such as periprosthetic orthopedic infections, has reinforced scientific interest. Extracellular DNA (eDNA) is a recently uncovered component that is proving to be almost omnipresent in the extracellular polymeric substance (EPS) of biofilm. This macromolecule is eliciting unprecedented consideration for the critical impact on the pathogenesis of chronic clinical infections. After a systematic review of the literature, an updated description of eDNA in biofilms is presented, with a special focus on the latest findings regarding its fundamental structural role and the contribution it makes to the complex architecture of bacterial biofilms through interactions with a variety of other molecular components of the biofilm matrix.

Broad-Spectrum Anti-Adhesive Coating Based on an Extracellular Polymer from a Marine Cyanobacterium

Medical device-associated infections are a major health threat, representing about half of all hospital-acquired infections. Current strategies to prevent this problem based on device coatings with antimicrobial compounds (antibiotics or antiseptics) have proven to be insufficient, often toxic, and even promoting bacterial resistance. Herein, we report the development of an infection-preventive coating (CyanoCoating) produced with an extracellular polymer released by the marine cyanobacterium Cyanothece sp. CCY 0110. CyanoCoating was prepared by spin-coating and its bacterial anti-adhesive efficiency was evaluated against relevant etiological agents (Staphylococcus aureus, S. epidermidis, Pseudomonas aeruginosa and Escherichia coli) and platelets, both in the presence or absence of human plasma proteins. CyanoCoating cytotoxicity was assessed using the L929 fibroblasts cell line. CyanoCoating exhibited a smooth topography, low thickness and high hydrophilic properties with mild negative charge. The non-cytotoxic CyanoCoating prevented adhesion of all the bacteria tested (≤80%) and platelets (<87%), without inducing platelet activation (even in the presence of plasma proteins). The significant reduction in protein adsorption (<77%) confirmed its anti-adhesive properties. The development of this anti-adhesive coating is an important step towards the establishment of a new technological platform capable of preventing medical device-associated infections, without inducing thrombus formation in blood-contacting applications.

Implantable Device-Related Infection

Over half of the nearly two million healthcare-associated infections can be attributed to indwelling medical devices. In this review, we highlight the difficulty in diagnosing implantable device-related infection and how this leads to a likely underestimate of the prevalence. We then provide a length-scale conceptualization of device-related infection pathogenesis. Within this conceptualization we focus specifically on biofilm formation and the role of host immune and coagulation systems. Using this framework, we describe how current and developing preventative strategies target specific processes along the entire length-scale. In light of the significant time horizon for the development and translation of new preventative technologies, we also emphasize the need for parallel development of in situ treatment strategies. Specific examples of both preventative and treatment strategies and how they align with the length-scale conceptualization are described.

Silver Nanocoating Technology in the Prevention of Prosthetic Joint Infection

Prosthetic joint infection (PJI) is a feared complication of total joint arthroplasty associated with increased morbidity and mortality. There is a growing body of evidence that bacterial colonization and biofilm formation are critical pathogenic events in PJI. Thus, the choice of biomaterials for implanted prostheses and their surface modifications may significantly influence the development of PJI. Currently, silver nanoparticle (AgNP) technology is receiving much interest in the field of orthopaedics for its antimicrobial properties and a strong anti-biofilm potential. The great advantage of AgNP surface modification is a minimal release of active substances into the surrounding tissue and a long period of effectiveness. As a result, a controlled release of AgNPs could ensure antibacterial protection throughout the life of the implant. Moreover, the antibacterial effect of AgNPs may be strengthened in combination with conventional antibiotics and other antimicrobial agents. Here, our main attention is devoted to general guidelines for the design of antibacterial biomaterials protected by AgNPs, its benefits, side effects and future perspectives in PJI prevention.

Antibacterial surface treatment for orthopaedic implants

It is expected that the projected increased usage of implantable devices in medicine will result in a natural rise in the number of infections related to these cases. Some patients are unable to autonomously prevent formation of biofilm on implant surfaces. Suppression of the local peri-implant immune response is an important contributory factor. Substantial avascular scar tissue encountered during revision joint replacement surgery places these cases at an especially high risk of periprosthetic joint infection. A critical pathogenic event in the process of biofilm formation is bacterial adhesion. Prevention of biomaterial-associated infections should be concurrently focused on at least two targets: inhibition of biofilm formation and minimizing local immune response suppression. Current knowledge of antimicrobial surface treatments suitable for prevention of prosthetic joint infection is reviewed. Several surface treatment modalities have been proposed. Minimizing bacterial adhesion, biofilm formation inhibition, and bactericidal approaches are discussed. The ultimate anti-infective surface should be “smart” and responsive to even the lowest bacterial load. While research in this field is promising, there appears to be a great discrepancy between proposed and clinically implemented strategies, and there is urgent need for translational science focusing on this topic.

Bacterial adhesion to poly-(D,L)lactic acid blended with vitamin E: toward gentle anti-infective biomaterials

Anti-infective properties of biomedical materials are often achieved by loading or coating them with powerful bactericides. Undesirably, these bioactive molecules can damage the host cells at the biomaterial-tissues interface and, sometimes, even determine systemic toxic effects. The search for biomaterials able to actively resist infection while displaying a safe cytocompatibility profile toward eukaryotic cells is being progressively developed. Poly-(D,L)lactic acid (PLA) is a broadly used resorbable material with established biocompatibility properties. The dissolving surfaces of a biodegradable material tend to be per se elusive for bacteria. Here, films of pristine PLA, of PLA blended with vitamin E (VitE) and PLA blended with vitamin E acetate (VitE ac) were challenged in vitro with the biofilm-producers Staphylococcus epidermidis RP62A and Staphylococcus aureus ATCC25923. The bacterial adhesion properties of the different materials were investigated on small film disc specimens by a method based on microtiter plates. Adherent bacteria were quantified by both CFU plating and bioluminescence. Significant decrease in bacterial adhesion and biofilm accumulation was found on the surface of both the enriched polymers. These findings, together with the favorable intrinsic properties of PLA and the desirable bioactivities conferred by VitE, point up the VitE-blended PLA polymers as gentle anti-infective biomaterials.

The interaction of bacteria with engineered nanostructured polymeric materials: a review

Bacterial infections are a leading cause of morbidity and mortality worldwide. In spite of great advances in biomaterials research and development, a significant proportion of medical devices undergo bacterial colonization and become the target of an implant-related infection. We present a review of the two major classes of antibacterial nanostructured materials: polymeric nanocomposites and surface-engineered materials. The paper describes antibacterial effects due to the induced material properties, along with the principles of bacterial adhesion and the biofilm formation process. Methods for antimicrobial modifications of polymers using a nanocomposite approach as well as surface modification procedures are surveyed and discussed, followed by a concise examination of techniques used in estimating bacteria/material interactions. Finally, we present an outline of future sceneries and perspectives on antibacterial applications of nanostructured materials to resist or counteract implant infections.