An antibiofilm coating of 5-aryl-2-aminoimidazole covalently attached to a titanium surface

EPS inhibitor treatment of Salmonella impacts evolution without selecting for resistance to biofilm inhibition

Virulence factors of pathogens, such as toxin production and biofilm formation, often exhibit a public character, providing benefits to nearby non-producers. Consequently, anti-virulence drugs targeting these public traits may not select for resistance, as resistant mutants that resume production of the virulence factor share the benefits of their resistance with surrounding sensitive cells. In agreement with this, we show that even after long-term treatment with a 2-amino-imidazole (2-AI) biofilm inhibitor, Salmonella populations remained as susceptible to biofilm inhibition as the ancestral populations. Nonetheless, further genotypic and phenotypic analysis revealed that the Salmonella populations did adapt to the treatment and accumulated mutations in efflux pump regulators and alternative sigma factors. These mutations resulted in a reduced biofilm-forming capacity and increased efflux activity. Their selection was due to a growth delaying side effect of the biofilm inhibitor. Enhanced efflux activity helped overcome this growth delay, providing a fitness advantage over the ancestor. Finally, we demonstrate that chemical modification of the inhibitor enhances its specificity by partially alleviating the unintended growth delay while retaining the anti-biofilm activity, which in turn eliminated the selection pressure for increased efflux. Overall, our findings highlight that while unintended side effects can complicate anti-virulence strategies, adaptation to these effects does not necessarily restore the inhibited virulence trait. Moreover, chemical modification can mitigate these unintended side effects and enhance drug specificity.

Optimizing biofilm inhibitors: Balancing activity and toxicity in 2N-aminated 5-aryl-2-aminoimidazoles

To evaluate the effect of amination on biofilm inhibition against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, representative compounds of two previously described 5-aryl-2-aminoimidazole (5-Ar-2-AI) classes were aminated by installing an amino group at the end of the substituted n-alkyl chain. Amination led to an improvement in activity for one of the two classes, the 2N-substituted 5-Ar-2-AI class. Based on these findings, a more extensive library of 2N-substituted-aminated 5-Ar-2-AIs was synthesized having different n-alkyl and halogen substitutions on the 2N-position and the 4(5)-phenyl ring, respectively. Compounds were evaluated for their biofilm inhibitory activity against E. coli, P. aeruginosa, S. aureus, Staphylococcus epidermidis and MRSA. Additionally, their toxicity was tested on eight continuous cell lines, peripheral blood mononuclear cells and Caenorhabditis elegans, along with their genotoxicity on Capan-1. Halogenation and elongation of the n-alkyl substituent showed a positive effect on biofilm inhibitory activity, but also increased toxicity. Compromising between activity and toxicity, a non-halogenated 2N-substituted-aminated 5-Ar-2-AI compound with an intermediate n-heptyl substitution demonstrated promising broad-spectrum biofilm inhibition, making it a suitable candidate for further research in anti-infectious medical applications.

Biocompatibility Analysis of the Silver-Coated Microporous Titanium Implants Manufactured with 3D-Printing Technology

3D-printed microporous titanium scaffolds enjoy good biointegration with the residuum's soft and bone tissues, and they promote excellent biomechanical properties in attached prostheses. Implant-associated infection, however, remains a major clinical challenge. Silver-based implant coatings can potentially reduce bacterial growth and inhibit biofilm formation, thereby reducing the risk of periprosthetic infections. In the current study, a 1-µm thick silver coating was prepared on the surface of a 3D-printed microporous titanium alloy with physical vapor deposition (PVD), with a final silver content of 1.00 ± 02 mg/cm2. Cell viability was evaluated with an MTT assay of MC3T3-E1 osteoblasts and human dermal fibroblasts cultured on the surface of the implants, and showed low cytotoxicity for cells during the 14-day follow-up period. Quantitative real-time polymerase chain reaction (RT-PCR) analysis of the relative gene expression of the extracellular matrix components (fibronectin, vitronectin, type I collagen) and cell adhesion markers (α2, α5, αV, β1 integrins) in dermal fibroblasts showed that cell adhesion was not reduced by the silver coating of the microporous implants. An RT-PCR analysis of gene expression related to osteogenic differentiation, including TGF-β1, SMAD4, osteocalcin, osteopontin, and osteonectin in MC3T3-E1 osteoblasts, demonstrated that silver coating did not reduce the osteogenic activity of cells and, to the contrary, enhanced the activity of the TGF-β signaling pathway. For representative sample S5 on day 14, the gene expression levels were 7.15 ± 0.29 (osteonectin), 6.08 ± 0.12 (osteocalcin), and 11.19 ± 0.77 (osteopontin). In conclusion, the data indicate that the silver coating of the microporous titanium implants did not reduce the biointegrative or osteoinductive properties of the titanium scaffold, a finding that argues in favor of applying this coating in designing personalized osseointegrated implants.

Current Progress and Future Perspectives in Contact and Releasing-Type Antimicrobial Coatings of Orthopaedic Implants: A Systematic Review Analysis Emanated from In Vitro and In Vivo Models

Background: Despite the expanding use of orthopedic devices and the application of strict pre- and postoperative protocols, the elimination of postoperative implant-related infections remains a challenge. Objectives: To identify and assess the in vitro and in vivo properties of antimicrobial-, silver- and iodine-based implants, as well as to present novel approaches to surface modifications of orthopedic implants. Methods: A systematic computer-based review on the development of these implants, on PubMed and Web of Science databases, was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results: Overall, 31 in vitro and 40 in vivo entries were evaluated. Regarding the in vitro studies, antimicrobial-based coatings were assessed in 12 entries, silver-based coatings in 10, iodine-based in 1, and novel-applied coating technologies in 8 entries. Regarding the in vivo studies, antimicrobial coatings were evaluated in 23 entries, silver-coated implants in 12, and iodine-coated in 1 entry, respectively. The application of novel coatings was studied in the rest of the cases (4). Antimicrobial efficacy was examined using different bacterial strains, and osseointegration ability and biocompatibility were examined in eukaryotic cells and different animal models, including rats, rabbits, and sheep. Conclusions: Assessment of both in vivo and in vitro studies revealed a wide antimicrobial spectrum of the coated implants, related to reduced bacterial growth, inhibition of biofilm formation, and unaffected or enhanced osseointegration, emphasizing the importance of the application of surface modification techniques as an alternative for the treatment of orthopedic implant infections in the clinical settings.

Combination of Cefditoren and N-acetyl-l-Cysteine Shows a Synergistic Effect against Multidrug-Resistant Streptococcus pneumoniae Biofilms

Biofilm formation by Streptococcus pneumoniae is associated with colonization of the upper respiratory tract, including the carrier state, and with chronic respiratory infections in patients suffering from chronic obstructive pulmonary disease (COPD). The use of antibiotics alone to treat recalcitrant infections caused by biofilms is insufficient in many cases, requiring novel strategies based on a combination of antibiotics with other agents, including antibodies, enzybiotics, and antioxidants. In this work, we demonstrate that the third-generation oral cephalosporin cefditoren (CDN) and the antioxidant N-acetyl-l-cysteine (NAC) are synergistic against pneumococcal biofilms. Additionally, the combination of CDN and NAC resulted in the inhibition of bacterial growth (planktonic and biofilm cells) and destruction of the biofilm biomass. This marked antimicrobial effect was also observed in terms of viability in both inhibition (prevention) and disaggregation (treatment) assays. Moreover, the use of CDN and NAC reduced bacterial adhesion to human lung epithelial cells, confirming that this strategy of combining these two compounds is effective against resistant pneumococcal strains colonizing the lung epithelium. Finally, administration of CDN and NAC in mice suffering acute pneumococcal pneumonia caused by a multidrug-resistant strain was effective in clearing the bacteria from the respiratory tract in comparison to treatment with either compound alone. Overall, these results demonstrate that the combination of oral cephalosporins and antioxidants, such as CDN and NAC, respectively, is a promising strategy against respiratory biofilms caused by S. pneumoniae. IMPORTANCE Streptococcus pneumoniae is one of the deadliest bacterial pathogens, accounting for up to 2 million deaths annually prior to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccines have decreased the burden of diseases produced by S. pneumoniae, but the rise of antibiotic-resistant strains and nonvaccine serotypes is worrisome. Pneumococcal biofilms are associated with chronic respiratory infections, and treatment is challenging, making the search for new antibiofilm therapies a priority as biofilms become resistant to traditional antibiotics. In this work, we used the combination of an antibiotic (CDN) and an antioxidant (NAC) to treat the pneumococcal biofilms of relevant clinical isolates. We demonstrated a synergy between CDN and NAC that inhibited and treated pneumococcal biofilms, impaired pneumococcal adherence to the lung epithelium, and treated pneumonia in a mouse pneumonia model. We propose the widely used cephalosporin CDN and the repurposed drug NAC as a new antibiofilm therapy against S. pneumoniae biofilms, including those formed by antibiotic-resistant clinical isolates.

In vitro response of THP-1 derived macrophages to antimicrobially effective PHMB-coated Ti6Al4V alloy implant material with and without contamination with S. epidermidis and P. aeruginosa

AIM

Periprosthetic joint infections are a devastating complication after arthroplasty, leading to rejection of the prosthesis. The prevention of septic loosening may be possible by an antimicrobial coating of the implant surface. Poly (hexamethylene) biguanide hydrochloride [PHMB] seems to be a suitable antiseptic agent for this purpose since previous studies revealed a low cytotoxicity and a long-lasting microbicidal effect of Ti6Al4V alloy coated with PHMB. To preclude an excessive activation of the immune system, possible inflammatory effects on macrophages upon contact with PHMB-coated surfaces alone and after killing of S. epidermidis and P. aeruginosa are analyzed.

METHODS

THP-1 monocytes were differentiated to M0 macrophages by phorbol 12-myristate 13-acetate and seeded onto Ti6Al4V surfaces coated with various amounts of PHMB. Next to microscopic immunofluorescence analysis of labeled macrophages after adhesion on the coated surface, measurement of intracellular reactive oxygen species and analysis of cytokine secretion at different time points without and with previous bacterial contamination were conducted.

RESULTS

No influence on morphology of macrophages and only slight increases in iROS generation were detected. The cytokine secretion pattern depends on the surface treatment procedure and the amount of adsorbed PHMB. The PHMB coating resulted in a high reduction of viable bacteria, resulting in no significant differences in cytokine secretion as reaction to coated surfaces with and without bacterial burden.

CONCLUSION

Ti6Al4V specimens after alkaline treatment followed by coating with 5-7 μg PHMB and specimens treated with H2O2 before PHMB-coating (4 μg) had the smallest influence on the macrophage phienotype and thus are considered as the surface with the best cytocompatibility to macrophages tested in the present study.

Antibiotic-loaded amphora-shaped pores on a titanium implant surface enhance osteointegration and prevent infections

Artificial prostheses for joint replacement are indispensable in orthopedic surgery. Unfortunately, the implanted surface is attractive to not only host cells but also bacteria. To enable better osteointegration, a mechanically stable porous structure was created on a titanium surface using laser treatment and metallic silver particles were embedded in a hydrophilic titanium oxide layer on top. The laser structuring resulted in unique amphora-shaped pores. Due to their hydrophilic surface conditions and capillary forces, the pores can be loaded preoperative with the antibiotic of choice/need, such as gentamicin. Cytotoxicity and differentiation assays with primary human osteoblast-like cells revealed no negative effect of the surface modification with or without gentamicin loading. An in vivo biocompatibility study showed significantly enhanced osteointegration as measured by push-out testing and histomorphometry 56 days after the implantation of the K-wires into rat femora. Using a S. aureus infection model, the porous, silver-coated K-wires slightly reduced the signs of bone destruction, while the wires were still colonized after 28 days. Loading the amphora-shaped pores with gentamicin significantly reduced the histopathological signs of bone destruction and no bacteria were detected on the wires. Taken together, this novel surface modification can be applied to new or established orthopedic implants. It enables preoperative loading with the antibiotic of choice/need without further equipment or post-coating, and supports osteointegration without a negative effect of the released dug, such as gentamicin.

An Improved 2-Aminoimidazole Based Anti-Biofilm Coating for Orthopedic Implants: Activity, Stability, and in vivo Biocompatibility

Orthopedic device-related infections remain a serious challenge to treat. Central to these infections are bacterial biofilms that form on the orthopedic implant itself. These biofilms shield the bacteria from the host immune system and most common antibiotic drugs, which renders them essentially antibiotic-tolerant. There is an urgent clinical need for novel strategies to prevent these serious infections that do not involve conventional antibiotics. Recently, a novel antibiofilm coating for titanium surfaces was developed based on 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine as an active biofilm inhibitor. In the current study we present an optimized coating protocol that allowed for a 5-fold higher load of this active compound, whilst shortening the manufacturing process. When applied to titanium disks, the newly optimized coating was resilient to the most common sterilization procedures and it induced a 1 log reduction in biofilm cells of a clinical Staphylococcus aureus isolate (JAR060131) in vitro, without affecting the planktonic phase. Moreover, the antibiofilm effect of the coating in combination with the antibiotic cefuroxime was higher than cefuroxime treatment alone. Furthermore, the coating was successfully applied to a human-scale fracture fixation device resulting in a loading that was comparable to the titanium disk model. Finally, an in vivo biocompatibility and healing study in a rabbit osteotomy model indicated that these coated implants did not negatively affect fracture healing or osteointegration. These findings put our technology one step closer to clinical trials, confirming its potential in fighting orthopedic infections without compromising healing.

2-Aminoimidazoles as potent inhibitors of contaminating brewery biofilms

Cleaning and disinfection protocols are not always able to remove biofilm microbes present in breweries, indicating that novel anti-biofilm strategies are needed. The preventive activities of three in-house synthesized members of the 2-aminoimidazole class of anti-biofilm molecules were studied against 17 natural brewery biofilms and benchmarked against 18 known inhibitors. Two 2-aminoimidazoles belonged to the top six inhibitors, which were retested against 12 defined brewery biofilm models. For the three best inhibitors, tannic acid (n° 1), 2-aminoimidazole imi-AAC-5 (n° 2), and baicalein (n° 3), the effect on the microbial metabolic activity was evaluated. Here, the top three inhibitors showed similar effectiveness, with baicalein possessing a slightly higher efficacy. Even though the 2-aminoimidazole was the second-best inhibitor, it showed a lower biocidal activity than tannic acid, making it less prone to resistance evolution. Overall, this study supports the potential of 2-aminoimidazoles as a preventive anti-biofilm strategy.

Advances in Bacterial Biofilm Management for Maintaining Microbiome Homeostasis

Certain microbial biofilm in the human-microbiota community can negatively impact the host microbiome. This gives rise to various methods to prevent the formation of biofilms or to facilitate biofilm dispersal from surfaces and tissues in the host. Despite all these efforts, these persistent microbial biofilms on surfaces and in the host tissue can result in health problems to the host and its microbiome. It is the adaptive behavior of microbes within the biofilm that confers on these tenacious microbes the resistance to harsh environments, antibiotic treatments, and the ability to evade the host immune system. In this review, the approaches to combat microbial biofilm in the last decade are discussed. The biochemical pathway regulating biofilm formation is first discussed, followed by the discussion of the three approaches to combat biofilm formation: physical, chemical, and biological approaches. The advances in these approaches have given rise to methods of effectively dispersing the microbial biofilm and preventing the adherence of these microbial communities altogether. As there are numerous approaches to target biofilm, in this review the attempt is to provide insights on how these approaches have been used to modulate the host-microbiome by looking at the individual strengths and weaknesses.

Biodistribution, biocompatibility and targeted accumulation of magnetic nanoporous silica nanoparticles as drug carrier in orthopedics

BACKGROUND

In orthopedics, the treatment of implant-associated infections represents a high challenge. Especially, potent antibacterial effects at implant surfaces can only be achieved by the use of high doses of antibiotics, and still often fail. Drug-loaded magnetic nanoparticles are very promising for local selective therapy, enabling lower systemic antibiotic doses and reducing adverse side effects. The idea of the following study was the local accumulation of such nanoparticles by an externally applied magnetic field combined with a magnetizable implant. The examination of the biodistribution of the nanoparticles, their effective accumulation at the implant and possible adverse side effects were the focus. In a BALB/c mouse model (n = 50) ferritic steel 1.4521 and Ti90Al6V4 (control) implants were inserted subcutaneously at the hindlimbs. Afterwards, magnetic nanoporous silica nanoparticles (MNPSNPs), modified with rhodamine B isothiocyanate and polyethylene glycol-silane (PEG), were administered intravenously. Directly/1/7/21/42 day(s) after subsequent application of a magnetic field gradient produced by an electromagnet, the nanoparticle biodistribution was evaluated by smear samples, histology and multiphoton microscopy of organs. Additionally, a pathohistological examination was performed. Accumulation on and around implants was evaluated by droplet samples and histology.

RESULTS

Clinical and histological examinations showed no MNPSNP-associated changes in mice at all investigated time points. Although PEGylated, MNPSNPs were mainly trapped in lung, liver, and spleen. Over time, they showed two distributional patterns: early significant drops in blood, lung, and kidney and slow decreases in liver and spleen. The accumulation of MNPSNPs on the magnetizable implant and in its area was very low with no significant differences towards the control.

CONCLUSION

Despite massive nanoparticle capture by the mononuclear phagocyte system, no significant pathomorphological alterations were found in affected organs. This shows good biocompatibility of MNPSNPs after intravenous administration. The organ uptake led to insufficient availability of MNPSNPs in the implant region. For that reason, among others, the nanoparticles did not achieve targeted accumulation in the desired way, manifesting future research need. However, with different conditions and dimensions in humans and further modifications of the nanoparticles, this principle should enable reaching magnetizable implant surfaces at any time in any body region for a therapeutic reason.

Inhibiting bacterial cooperation is an evolutionarily robust anti-biofilm strategy

Bacteria commonly form dense biofilms encased in extracellular polymeric substances (EPS). Biofilms are often extremely tolerant to antimicrobials but their reliance on shared EPS may also be a weakness as social evolution theory predicts that inhibiting shared traits can select against resistance. Here we show that EPS of Salmonella biofilms is a cooperative trait whose benefit is shared among cells, and that EPS inhibition reduces both cell attachment and antimicrobial tolerance. We then compare an EPS inhibitor to conventional antimicrobials in an evolutionary experiment. While resistance against conventional antimicrobials rapidly evolves, we see no evolution of resistance to EPS inhibition. We further show that a resistant strain is outcompeted by a susceptible strain under EPS inhibitor treatment, explaining why resistance does not evolve. Our work suggests that targeting cooperative traits is a viable solution to the problem of antimicrobial resistance.

Bacterial biofilms rely on shared extracellular polymeric substances (EPS) and are often highly tolerant to antibiotics. Here, the authors show in in vitro experiments that Salmonella does not evolve resistance to EPS inhibition because such strains are outcompeted by a susceptible strain under inhibitor treatment.