An investigation of the antibacterial ability and cytotoxicity of a novel cu-bearing 317L stainless steel

The impact of alloying element Cu on corrosion and biofilms of 316L stainless steel exposed to seawater

Copper-containing stainless steel (SS) has been reported to mitigate biofilms in industrial and clinical environments. However, the impact of copper released from copper-containing SS in natural seawater on biofilms and corrosion is still unclear. In this study, three kinds of 316L SS were immersed in natural seawater for 6 months, and the pitting depth decreased in the order: 316L-Cu SS (annealed) > 316L SS > 316L-Cu SS (aged). The biofilm thickness and number of sessile cells on the surface of 316L-Cu SS (annealed) and 316L SS were similar but notably greater than those of 316L-Cu SS (aged). Furthermore, the results of the community analysis indicated that the addition of copper in 316L-Cu SS (aged) reduced the diversity and richness of the microbial community, resulting in a significant reduction in the number of genera constituting the biofilms. Copper ions exhibit a broad-spectrum bactericidal effect, effectively reducing the abundance of dominant populations and microbial genera in the biofilms, thereby mitigating pitting corrosion induced by microorganisms. In addition, the PCoA scatter plot showed that time also played an important role in the regulation of microbial community structure.

Microbially Influenced Corrosion of Steel in Marine Environments: A Review from Mechanisms to Prevention

Microbially influenced corrosion (MIC) is a formidable challenge in the marine industry, resulting from intricate interactions among various biochemical reactions and microbial species. Many preventions used to mitigate biocorrosion fail due to ignorance of the MIC mechanisms. This review provides a summary of the current research on microbial corrosion in marine environments, including corrosive microbes and biocorrosion mechanisms. We also summarized current strategies for inhibiting MIC and proposed future research directions for MIC mechanisms and prevention. This review aims to comprehensively understand marine microbial corrosion and contribute to novel strategy developments for biocorrosion control in marine environments.

Inhibition of microbial extracellular electron transfer corrosion of marine structural steel with multiple alloy elements

The microbial corrosion of marine structural steels (09CrCuSb low alloy steel (LAS) and Q235 carbon steel (CS)) in Desulfovibrio vulgaris medium and Pseudomonas aeruginosa medium based on seawater was investigated. In the D. vulgaris medium, the weight loss and maximum pit depth of 09CrCuSb LAS were 0.59 and 0.56 times as much as those of Q235 CS, respectively. Meanwhile, in the P. aeruginosa medium, the values were 0.53 and 0.67 times, respectively. Compared to Q235 CS, 09CrCuSb LAS contains more alloy elements (Cr, Ni, Cu, Al and Sb), which led to obvious inhibition of sessile bacteria growth but had no effect on planktonic bacteria. The number of live sessile cells on the 09CrCuSb LAS surface was 23.4 % and 26.9 % of that on the Q235 CS surface in the D. vulgaris medium and P. aeruginosa medium, respectively. Fewer sessile cells on the steel surface led to a lower extracellular electron transfer (EET) rate so that less corrosion occurred. In addition, the combined effect of alloying elements on grain refinement and passive film formation also improved the anti-corrosion property of the steels.

Osteoblastic Cell Responses of Copper Nanoparticle Coatings on Ti-6Al-7Nb Alloy Using Electrophoretic Deposition Method

Aim

To investigate and compare the cell cytotoxicity, proliferation, cell attachment, and morphology of human fetal osteoblasts (hFOB) cells of coated samples (titanium nanocopper (Ti Cu), titanium nanohydroxyapatite (Ti HA) and titanium nanocopper ion doped hydroxyapatite (Ti Cu/HA) and uncoated samples (Ti) in order to assess the suitability of these surface modifications on Ti-6Al-7Nb for dental implant application.

Materials and Methods

The cytotoxicity was studied by examining the hFOB cell response by MTT assessment. The cell morphology was evaluated by inverted microscopy and observed under scanning electronic microscopy (SEM).

Results

MTT assay results displayed that the Cu content on the surface of Ti-6Al-7Nb alloys did not produce any cytotoxic effect on cell viability. The cell viability rate in all samples ranges from 97% to 126%, indicating that hFOB cells grew at a high proliferation rate. However, no significant differences in cell viability were observed between Ti and Ti Cu and between Ti HA and Ti Cu/HA groups. Microscopic examination demonstrated no difference in the cell morphology of hFOB among all samples. In addition, SEM observation indicated favorable adhesion and spreading of the cells on the coated and uncoated samples.

Conclusions

The surface modification of Ti-6Al-7Nb alloy with Cu, HA, and Cu/HA exhibits good cell biocompatibility, and the Cu has no influence on the cell proliferation and differentiation of hFOB.

Anti-pathogen stainless steel combating COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exhibits strong stability on conventional stainless steel (SS) surface, with infectious virus detected even after two days, posing a high risk of virus transmission via surface touching in public areas. In order to mitigate the surface toughing transmission, the present study develops the first SS with excellent anti-pathogen properties against SARS-COV-2. The stabilities of SARS-CoV-2, H1N1 influenza A virus (H1N1), and Escherichia coli (E.coli) on the surfaces of Cu-contained SS, pure Cu, Ag-contained SS, and pure Ag were investigated. It is discovered that pure Ag and Ag-contained SS surfaces do not display apparent inhibitory effects on SARS-CoV-2 and H1N1. In comparison, both pure Cu and Cu-contained SS with a high Cu content exhibit significant antiviral properties. Significantly, the developed anti-pathogen SS with 20 wt% Cu can distinctly reduce 99.75% and 99.99% of viable SARS-CoV-2 on its surface within 3 and 6 h, respectively. In addition, the present anti-pathogen SS also exhibits an excellent inactivation ability for H1N1 influenza A virus (H1N1), and Escherichia coli (E.coli). Interestingly, the Cu ion concentration released from the anti-pathogen SS with 10 wt% and 20 wt% Cu was notably higher than the Ag ion concentration released from Ag and the Ag-contained SS. Lift buttons made of the present anti-pathogen SS are produced using mature powder metallurgy technique, demonstrating its potential applications in public areas and fighting the transmission of SARS-CoV-2 and other pathogens via surface touching.

Application of Copper Nanoparticles in Dentistry

Nanoparticles based on metal and metallic oxides have become a novel trend for dental applications. Metal nanoparticles are commonly used in dentistry for their exclusive shape-dependent properties, including their variable nano-sizes and forms, unique distribution, and large surface-area-to-volume ratio. These properties enhance the bio-physio-chemical functionalization, antimicrobial activity, and biocompatibility of the nanoparticles. Copper is an earth-abundant inexpensive metal, and its nanoparticle synthesis is cost effective. Copper nanoparticles readily intermix and bind with other metals, ceramics, and polymers, and they exhibit physiochemical stability in the compounds. Hence, copper nanoparticles are among the commonly used metal nanoparticles in dentistry. Copper nanoparticles have been used to enhance the physical and chemical properties of various dental materials, such as dental amalgam, restorative cements, adhesives, resins, endodontic-irrigation solutions, obturation materials, dental implants, and orthodontic archwires and brackets. The objective of this review is to provide an overview of copper nanoparticles and their applications in dentistry.

Inhibition efficiency of 304-Cu stainless steel against oral bacterial biofilm

PURPOSE

This study aims to evaluate the antibacterial properties of 304 Cu-bearing stainless steel (SS) with different Cu contents (0, 2.5, 4.5 wt.%) against oral biofilms of Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), and their mixture.

METHODS

Bacterial biofilms on the surface of 304-Cu SS were characterized by plate counting, 4', 6-diamidino-2-phenylindole (DAPI) staining with aid of sanning electron microscopy (SEM) and 2, 3-bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). In addition, the inhibition zone method was also employed to evaluate the antibacterial properties of 304-Cu SS. Cell Counting Kit-8 (CCK-8) and flow cytometry were used to assess the cytotoxicity and apoptosis rate of 304-Cu SS, respectively.

RESULTS

304-4.5Cu SS could effectively inhibit the attachment, formation, activity, and metabolism of bacterial biofilm, possessing the best antibacterial properties exceeding 99.9% of antibacterial rate against S. mutans, S. sanguinis, and their mixture. The diameters of inhibition zones to S. mutans and S. sanguinis on the surface of 304-4.5Cu SS were 21.7 and 14.7 mm, respectively. The results of cell experiments in vitro showed that both 304-2.5Cu SS and 304-4.5Cu SS had no evident cytotoxicity with an identical grade 1. The apoptosis rate exhibited a gradually increased tendency with increase of the Cu content in 304 SS.

CONCLUSIONS

304-4.5Cu SS without cytotoxic effect on NIH3T3 cells has obvious antibacterial activity against S. mutans, S. sanguinis and their mixture.

CLINICAL SIGNIFICANCE

The Cu-bearing stainless steel provides a new solution to be used as oral orthodontic devices for inhibiting oral microflora imbalance and enamel demineralization.

Plasma SiOx:H Nanocoatings to Enhance the Antibacterial and Anti-Inflammatory Properties of Biomaterials

Purpose

Materials and Methods

Results

Conclusion

Biological applications of copper-containing materials

Copper is an indispensable trace metal element in the human body, which is mainly absorbed in the stomach and small intestine and excreted into the bile. Copper is an important component and catalytic agent of many enzymes and proteins in the body, so it can influence human health through multiple mechanisms. Based on the biological functions and benefits of copper, an increasing number of researchers in the field of biomaterials have focused on developing novel copper-containing biomaterials, which exhibit unique properties in protecting the cardiovascular system, promoting bone fracture healing, and exerting antibacterial effects. Copper can also be used in promoting incisional wounds healing, killing cancer cells, Positron Emission Tomography (PET) imaging, radioimmunological tracing and radiotherapy of cancer. In the present review, the biological functions of copper in the human body are presented, along with an overview of recent progress in our understanding of the biological applications and development of copper-containing materials. Furthermore, this review also provides the prospective on the challenges of those novel biomaterials for future clinical applications.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys, including stainless steel, titanium and its alloys, cobalt alloys, and other metals and alloys have been widely used clinically as implant materials, but implant-related infection or inflammation is still one of the main causes of implantation failure. The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint. Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability, good mechanical properties and good biocompatibility in vitro and in vivo. In this review, common antibacterial alloying elements, antibacterial standards and testing methods were introduced. Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail, including antibacterial stainless steel, antibacterial titanium alloy, antibacterial zinc and alloy, antibacterial magnesium and alloy, antibacterial cobalt alloy, and other antibacterial metals and alloys. Researches on the antibacterial properties, mechanical properties, corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time. It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner, thereby could promote the development of antibacterial metal alloys and the clinical application.

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This paper focuses the recent development of several antibacterial metals and alloys as biomedical materials.

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The possible antibacterial mechanisms of antibacterial metals and alloys are summarized in this paper.

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This review discusses the feasibility of antibacterial metals and alloys as biomedical implants in the future.

Copper-Containing Alloy as Immunoregulatory Material in Bone Regeneration via Mitochondrial Oxidative Stress

In the mammalian skeletal system, osteogenesis and angiogenesis are closely linked by type H vessels during bone regeneration and repair. Our previous studies confirmed the promotion of these processes by copper-containing metal (CCM) in vitro and in vivo. However, whether and how the coupling of angiogenesis and osteogenesis participates in the promotion of bone regeneration by CCM in vivo is unknown. In this study, M2a macrophages but not M2c macrophages were shown to be immunoregulated by CCM. A CCM, 316L−5Cu, was applied to drilling hole injuries of the tibia of C57/6 mice for comparison. We observed advanced formation of cortical bone and type H vessels beneath the new bone in the 316L−5Cu group 14 and 21 days postinjury. Moreover, the recruitment of CD206-positive M2a macrophages, which are regarded as the primary source of platelet-derived growth factor type BB (PDGF-BB), was significantly promoted at the injury site at days 14 and 21. Under the stimulation of CCM, mitochondria-derived reactive oxygen species were also found to be upregulated in CD206^hi M2a macrophages in vitro, and this upregulation was correlated with the expression of PDGF-BB. In conclusion, our results indicate that CCM promotes the evolution of callus through the generation of type H vessels during the process of bone repair by upregulating the expression of PDGF-BB derived from M2a macrophages.

Antibacterial effect of a copper-containing titanium alloy against implant-associated infection induced by methicillin-resistant Staphylococcus aureus

Implant-associated infection (IAI) induced by methicillin-resistant Staphylococcus aureus (MRSA) is a devastating complication in the orthopedic clinic. Traditional implant materials, such as Ti6Al4V, are vulnerable to microbial infection. In this study, we fabricated a copper (Cu)-containing titanium alloy (Ti6Al4V-Cu) for the prevention and treatment of MRSA-induced IAI. The material characteristics, antibacterial activity, and biocompatibility of Ti6Al4V-Cu were systematically investigated and compared with those of Ti6Al4V. Ti6Al4V-Cu provided stable and continuous Cu²⁺ release, at a rate of 0.106 mg/cm²/d. Its antibacterial performance against MRSA in vitro was confirmed by plate counting analysis, crystal violet staining, and scanning electron microscopic observations. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis demonstrated that Ti6Al4V-Cu suppressed biofilm formation, virulence, and antibiotic-resistance of MRSA. The in vivo anti-MRSA effect was investigated in a rat IAI model. Implants were contaminated with MRSA solution, implanted into the femur, and left for 6 weeks. Severe IAI developed in the Ti6Al4V group, with increased radiological score (9.6 ± 1.3) and high histological score (10.1 ± 1.9). However, no sign of infection was found in the Ti6Al4V-Cu group, as indicated by decreased radiological score (1.3 ± 0.4) and low histological score (2.3 ± 0.5). In addition, Ti6Al4V-Cu had favorable biocompatibility both in vitro and in vivo. In summary, Ti6Al4V-Cu is a promising implant material to protect against MRSA-induced IAI.

Biodegradable Zn-Cu alloys show antibacterial activity against MRSA bone infection by inhibiting pathogen adhesion and biofilm formation

Bone and joint-related infections remain the primary and most critical complications of orthopedic surgery. We have innovatively prepared Zn-Cu alloys to achieve outstanding material and antibacterial properties. In this study, we systematically assessed the material properties and antibacterial activity of these Zn-Cu alloys. Our results showed that the Zn-2Cu alloy had the best mechanical properties, biocompatibility, and osteogenic properties. Findings of microbial cultures, CLSM, SEM, and TEM indicated that Zn-2Cu alloy can inhibit both coagulase-positive and coagulase-negative staphylococci, as well as antibiotic-resistant strains (MRSA and MRSE), by preventing the bacteria adhesion and the biofilm formation. Zn-2Cu alloy could broadly affect the expression of MRSA genes associated with adhesion, autolysis, biofilm formation, virulence, and drug resistance. A rat femur intramedullary nail infection-prevention model was established and the Zn-2Cu alloy-treated group showed significant antibacterial activity against MRSA and reduced the inflammatory toxic side-effects and infection-related bone loss. Collectively, our results indicate the potential utility of Zn-Cu alloy implants with 2 wt% Cu in treating orthopedic infections. Statement of significance: Osteomyelitis is a serious complication of orthopedic surgeries. Wide use of antibiotics contributes to the appearance of multi-drug resistant strains like methicillin-resistant staphylococcus aureus (MRSA). Alternatively, anti-osteomyelitis implants with broad-spectrum antibacterial properties can be favorable. Here, the antibacterial performance of biodegradable Zn-Cu alloys was evaluated with four different bacteria strains including antibiotic-resistant strains (MRSA and MRSE). Zn-Cu alloys exert excellent bacterial killing capability in all strains. In a rat femur infection model, the alloy showed significant antibacterial activity against MRSA and reduced inflammatory toxic side-effects as well as infection-related bone loss. The antibacterial property of Zn-2Cu alloy was associated with inhibition of gene expression related to wall synthesis, adhesion, colonization, biofilm formation, autolysis, and secretion of virulence factors in MRSA.

Multifunctional Copper-Containing Mesoporous Glass Nanoparticles as Antibacterial and Proangiogenic Agents for Chronic Wounds

The physiological wound healing process involves a cascade of events which could be affected by several factors resulting in chronic, non-healing wounds. The latter represent a great burden especially when bacterial biofilms are formed. The rise in antibiotic resistance amongst infectious microorganisms leads to the need of novel approaches to treat this clinical issue. In this context, the use of advanced biomaterials, which can enhance the physiological expression and secretion of the growth factors involved in the wound healing process, is gaining increasing attention as a robust and appealing alternative approach. Among them, mesoporous glasses are of particular interest due to their excellent textural properties and to the possibility of incorporating and releasing specific therapeutic species, such as metallic ions. One of the most attractive therapeutic ions is copper thanks to its proangiogenic and antibacterial effects. In this contribution, copper containing mesoporous glass nanoparticles were proposed as a multifunctional device to treat chronic wounds. The developed nanoparticles evidenced a very high specific surface area (740 m²/g), uniform pores of 4 nm and an almost total release of the therapeutic ion within 72 h of soaking. The produced nanoparticles were biocompatible and, when tested against Gram positive and Gram negative bacterial species, demonstrated antibacterial activity against both planktonic and biofilm bacteria in 2D cell monolayers, and in a 3D human model of infected skin. Their proangiogenic effect was tested with both the aortic ring and the chick chorioallantoic membrane assays and an increase in endothelial cell outgrowth at a concentration range between 30 and 300 ng/mL was shown. Overall, in this study biocompatible, multifunctional Cu-containing mesoporous glass nanoparticles were successfully produced and demonstrated to exert both antibacterial and proangiogenic effects.

The inhibitory mechanism of aurintricarboxylic acid targeting serine/threonine phosphatase Stp1 in Staphylococcus aureus: insights from molecular dynamics simulations

Serine/threonine phosphatase (Stp1) is a member of the bacterial Mg2+- or Mn2+- dependent protein phosphatase/protein phosphatase 2C family, which is involved in the regulation of Staphylococcus aureus virulence. Aurintricarboxylic acid (ATA) is a known Stp1 inhibitor with an IC50 of 1.03 μM, but its inhibitory mechanism has not been elucidated in detail because the Stp1-ATA cocrystal structure has not been determined thus far. In this study, we performed 400 ns molecular dynamics (MD) simulations of the apo-Stp1 and Stp1-ATA complex models. During MD simulations, the flap subdomain of the Stp1-ATA complex experienced a clear conformational transition from an open state to a closed state, whereas the flap domain of apo-Stp1 changed from an open state to a semi-open state. In the Stp1-ATA complex model, the hydrogen bond (H-bond) between D137 and N142 disappeared, whereas critical H-bond interactions were formed between Q160 and H13, Q160/R161 and ATA, as well as N162 and D198. Finally, four residues (D137, N142, Q160, and R161) in Stp1 were mutated to alanine and the mutant enzymes were assessed using phosphate enzyme activity assays, which confirmed their important roles in maintaining Stp1 activity. This study indicated the inhibitory mechanism of ATA targeting Stp1 using MD simulations and sheds light on the future design of allosteric Stp1 inhibitors.

Biofilm Inhibition via Delivery of Novel Methylthioadenosine Nucleosidase Inhibitors from PVA-Tyramine Hydrogels while Supporting Mesenchymal Stromal Cell Viability

The rise of antibiotic resistance, coupled with increased expectations for mobility in later life, is creating a need for biofilm inhibitors and delivery systems that will reduce surgical implant infection. A limitation of some of these existing delivery approaches is toxicity exhibited toward host cells. Here, we report the application of a novel inhibitor of the enzyme, methylthioadenosine nucleosidase (MTAN), a key enzyme in bacterial metabolic pathways, which include S-adenosylmethionine catabolism and purine nucleotide recycling, in combination with a poly(vinyl alcohol)-tyramine-based (PVA-Tyr) hydrogel delivery system. We demonstrate that a lead MTAN inhibitor, selected from a screened library of 34 candidates, (2S)-2-(4-amino-5H-pyrrolo3,2-dpyrimidin-7-ylmethyl)aminoundecan-1-ol (31), showed a minimum biofilm inhibitory concentration of 2.2 ± 0.4 μM against a clinical staphylococcal species isolated from an infected implant. We observed that extracellular DNA, a key constituent of biofilms, is significantly reduced when treated with 10 μM compound 31, along with a decrease in biofilm thickness. Compound 31 was incorporated into a hydrolytically degradable photo-cross-linked PVA-Tyr hydrogel and the release profile was evaluated by HPLC studies. Compound 31 released from the PVA-hydrogel system significantly reduced biofilm formation (77.2 ± 8.4% biofilm inhibition). Finally, compound 31 released from PVA-Tyr showed no negative impact on human bone marrow stromal cell (MSC) viability, proliferation, or morphology. The results demonstrate the potential utility of MTAN inhibitors in treating infections caused by Gram-positive bacteria, and the development of a nontoxic release system that has potential for tunability for time scale of delivery.

An antibacterial and biocompatible piperazine polymer

Bacterial repellence by biomedical materials is a desirable property that can potentially improve the healing process. In this study, we described a simple and green method to prepare a novel piperazine polymer (PE), which was based on the raw materials piperazine (PA) and ethylenediaminetetraacetic dianhydride (EDTAD). The structure and thermal stability of the obtained material were characterized using Fourier transform infrared spectrometry (FTIR), nuclear magnetic resonance spectroscopy (NMR), elementary analysis, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). To evaluate the antibacterial properties of PE, a strain of Gram-negative Escherichia coli (E. coli) bacteria and a strain of Gram-positive Staphylococcus aureus (S. aureus) bacteria were used. The results indicated that PE exhibited good antibacterial activity against both strains of bacteria in a short time frame. The initial cytotoxicity test of the obtained material was based on the changes in the morphology and proliferation of osteoblasts, and the results demonstrated that the cytotoxicity of PE was concentration-dependent. Combining the experimental results of these two parts, it was shown that bacteria could be inhibited by a certain concentration of PE, while its toxicity toward osteoblasts was very low. In summary, these results revealed the potential usefulness of PE in biomedical applications.

A novel piperazine polymer (PE), which was prepared through a simple and green method, exhibited good antibacterial activity against E. coli and S. aureus.

Nano-copper-bearing stainless steel promotes fracture healing by accelerating the callus evolution process

Treatment for fractures requires internal fixation devices, which are mainly produced from stainless steel or titanium alloy without biological functions. Therefore, we developed a novel nano-copper-bearing stainless steel with nano-sized copper-precipitation (317L-Cu SS). Based on previous studies, this work explores the effect of 317L-Cu SS on fracture healing; that is, proliferation, osteogenic differentiation, osteogenesis-related gene expression, and lysyl oxidase activity of human bone mesenchymal stem cells were detected in vitro. Sprague–Dawley rats were used to build an animal fracture model, and fracture healing and callus evolution were investigated by radiology (X-ray and micro-CT), histology (H&E, Masson, and safranin O/fast green staining), and histomorphometry. Further, the Cu²⁺ content and Runx2 level in the callus were determined, and local mechanical test of the fracture was performed to assess the healing quality. Our results revealed that 317L-Cu SS did not affect the proliferation of human bone mesenchymal stem cells, but promoted osteogenic differentiation and the expression of osteogenesis-related genes. In addition, 317L-Cu SS upregulated the lysyl oxidase activity. The X-ray and micro-CT results showed that the callus evolution efficiency and fracture healing speed were superior for 317L-Cu SS. Histological staining displayed large amounts of fibrous tissues at 3 weeks, and cartilage and new bone at 6 weeks. Further, histomorphometric analysis indicated that the callus possessed higher osteogenic efficiency at 6 weeks, and a high Cu²⁺ content and increased Runx2 expression were observed in the callus for 317L-Cu SS. Besides, the mechanical strength of the fracture site was much better than that of the control group. Overall, we conclude that 317L-Cu SS possesses the ability to increase Cu²⁺ content and promote osteogenesis in the callus, which could accelerate the callus evolution process and bone formation to provide faster and better fracture healing.

Characterisation of the Chemical Composition and Structural Features of Novel Antimicrobial Nanoparticles

Three antimicrobial nanoparticle types (AMNP0, AMNP1, and AMNP2) produced using the Tesima^TM thermal plasma technology were investigated and their compositions were determined using a combination of analytical methods. Scanning electron micrographs provided the morphology of these particles with observed sizes ranging from 10 to 50 nm, whilst FTIR spectra confirmed the absence of polar bonds and organic impurities, and strong Raman active vibrational bands at ca. 1604 and 1311 cm^-1 ascribed to C-C vibrational motions were observed. Carbon signals that resonated at δ_C 126 ppm in the solid state NMR spectra confirmed that sp² hybridised carbons were present in high concentration in two of the nanoparticle types (AMNP1 and AMNP2). X-ray powder diffraction suggested that AMNP0 contains single phase Tungsten carbide (WC) in a high state of purity and multiple phases of WC/WC_1-x were identified in both AMNP1 and AMNP2. Finally, X-ray photoelectron spectral (XPS) analyses revealed and quantified the elemental ratios in these composite formulations.

Inhibition of Staphylococcus aureus biofilm by Lactobacillus isolated from fine cocoa

BACKGROUND

Biofilm production represents an important virulence and pathogenesis factor for Staphylococcus aureus. The formation of biofilms on medical devices is a major concern in hospital environments, as they can become a constant source of infection. Probiotic bacteria, such as Lactobacillus fermentum and L. plantarum, have been found to inhibit biofilm formation; however little is known about the underlying mechanism. In this study, we tested the activity of supernatants produced by L. fermentum TCUESC01 and L. plantarum TCUESC02, isolated during the fermentation of fine cocoa, against S. aureus CCMB262 biofilm production. We measured inhibition of biofilm formation in vitro and analyzed biofilm structure by confocal and electronic microscopy. Additionally, we quantified the expression of S. aureus genes icaA and icaR involved in the synthesis of the biofilm matrix by real-time PCR.

RESULTS

Both Lactobacillus supernatants inhibited S. aureus growth. However, only L. fermentum TCUESC01 significantly reduced the thickness of the biofilm, from 14 μm to 2.83 μm (at 18 mg∙mL^-1, 90 % of the minimum inhibitory concentration, MIC), 3.12 μm (at 14 mg∙mL^-1, 70 % of the MIC), and 5.21 μm (at 10 mg∙mL^-1, 50 % of the MIC). Additionally, L. fermentum TCUESC01 supernatant modulated the expression of icaA and icaR.

CONCLUSIONS

L. fermentum TCUESC01 reduces the formation of S. aureus biofilm under subinhibitory conditions. Inhibition of biofilm production probably depends on modulation of the ica operon.