Oxidative Stress Response and E. coli Biofilm Formation under the Effect of Pristine and Modified Carbon Nanotubes

Carbon-Based Nanomaterials Alter the Behavior and Gene Expression Patterns of Bacteria

One of the most dangerous characteristics of bacteria is their propensity to form biofilms and their resistance to the drugs used in clinical practice today. The total number of genes that can be categorized as virulence genes ranges from a few hundred to more than a thousand. The bacteria employ a variety of mechanisms to regulate the expression of these genes in a coordinated manner during infection. The search for new agents with anti-virulence capacity is therefore crucial. Nanotechnology provides safe platforms for targeted therapies to combat a broad spectrum of microbial infections. As a new class of innovative materials, carbon-based nanomaterials (CBNs), which include carbon dots, carbon nanotubes, graphene, and fullerenes can have strong antibacterial activity. Exposure to CBNs has been shown to affect bacterial gene expression patterns. This study investigated the effect of CBNs on the repression of specific genes related to bacterial virulence/pathogenicity.

Therapeutic and diagnostic applications of carbon nanotubes in cancer: recent advances and challenges

Carbon nanotubes (CNTs) are allotropes of carbon, composed of carbon atoms forming a tube-like structure. Their high surface area, chemical stability, and rich electronic polyaromatic structure facilitate their drug-carrying capacity. Therefore, CNTs have been intensively explored for several biomedical applications, including as a potential treatment option for cancer. By incorporating smart fabrication strategies, CNTs can be designed to specifically target cancer cells. This targeted drug delivery approach not only maximizes the therapeutic utility of CNTs but also minimizes any potential side effects of free drug molecules. CNTs can also be utilised for photothermal therapy (PTT) which uses photosensitizers to generate reactive oxygen species (ROS) to kill cancer cells, and in immunotherapeutic applications. Regarding the latter, for example, CNT-based formulations can preferentially target intra-tumoural regulatory T-cells. CNTs also act as efficient antigen presenters. With their capabilities for photoacoustic, fluorescent and Raman imaging, CNTs are excellent diagnostic tools as well. Further, metallic nanoparticles, such as gold or silver nanoparticles, are combined with CNTs to create nanobiosensors to measure biological reactions. This review focuses on current knowledge about the theranostic potential of CNT, challenges associated with their large-scale production, their possible side effects and important parameters to consider when exploring their clinical usage.

Metabolic and Morphological Aspects of Adaptation of Alkaliphilic Bacillus aequororis 5-DB and Alkali-Tolerant Bacillus subtilis ATCC 6633 to Changes in pH and Mineralization

The goal of the study is to evaluate metabolic and morphological changes of the facultative alkaliphile Bacillus aequororis 5-DB and the weakly alkali-resistant B. subtilis ATCC 6633 in a wide pH range and at different NaCl concentrations. The alkaliphile B. aequororis 5-DB is shown to have a broader general resistance to adverse factors (wide pH range, 50 g/L NaCl) than a weakly alkali-tolerant strain of the same genus. This alkaliphile is also shown to have a significantly greater resistance not only to high pH but also to low pH in comparison with B. subtilis ATCC 6633. The resistance of B. aequororis 5-DB to low pH was expressed in higher metabolic activity, maintenance of ΔpH, and no significant cell damage. The selected set of methods (reduction of resazurin to resorufin by cell dehydrogenases, bioluminescent method for determining ATP, AFM, and measurement of intracellular pH) allows us to adequately assess the ability of microbial cells to withstand harsh environmental factors. Nonspecific resistance of B. aequororis 5-DB was proven using a complex of selected methods. Tolerance to a wide range of pH and high salt concentrations may be useful for biotechnological applications of the strain.

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Antibiofilm Effect of Nitric Acid-Functionalized Carbon Nanotube-Based Surfaces against E. coli and S. aureus

Chemically modified carbon nanotubes are recognized as effective materials for tackling bacterial infections. In this study, pristine multi-walled carbon nanotubes (p-MWCNTs) were functionalized with nitric acid (f-MWCNTs), followed by thermal treatment at 600 °C, and incorporated into a poly(dimethylsiloxane) (PDMS) matrix. The materials' textural properties were evaluated, and the roughness and morphology of MWCNT/PDMS composites were assessed using optical profilometry and scanning electron microscopy, respectively. The antibiofilm activity of MWCNT/PDMS surfaces was determined by quantifying culturable Escherichia coli and Staphylococcus aureus after 24 h of biofilm formation. Additionally, the antibacterial mechanisms of MWCNT materials were identified by flow cytometry, and the cytotoxicity of MWCNT/PDMS composites was tested against human kidney (HK-2) cells. The results revealed that the antimicrobial activity of MWCNTs incorporated into a PDMS matrix can be efficiently tailored through nitric acid functionalization, and it can be increased by up to 49% in the absence of surface carboxylic groups in f-MWCNT samples heated at 600 °C and the presence of redox activity of carbonyl groups. MWCNT materials changed the membrane permeability of both Gram-negative and Gram-positive bacteria, while they only induced the production of ROS in Gram-positive bacteria. Furthermore, the synthesized composites did not impact HK-2 cell viability, confirming the biocompatibility of MWCNT composites.