Differential toxicity of Al2O3 particles on Gram-positive and Gram-negative sediment bacterial isolates from freshwater

Oxidative stress, biofilm-formation and activity responses of P. aeruginosa to microplastic-treated sediments: Effect of temperature and sediment type

Climate change and plastic pollution are the big environmental problems that the environment and humanity have faced in the past and will face in many decades to come. Sediments are affected by many pollutants and conditions, and the behaviors of microorganisms in environment may be influenced due to changes in sediments. Therefore, the current study aimed to explore the differential effects of various microplastics and temperature on different sediments through the metabolic and oxidative responses of gram-negative Pseudomonas aeruginosa. The sediments collected from various fields including beaches, deep-sea discharge, and marine industrial areas. Each sediment was extracted and then treated with various microplastics under different temperature (-18, +4, +20 and 35 °C) for seven days. Then microplastics were removed from the suspension and microplastic-exposed sediment samples were incubated with Pseudomonas aeruginosa to test bacterial activity, biofilm, and oxidative characteristics. The results showed that both the activity and the biofilm formation of Pseudomonas aeruginosa increased with the temperature of microplastic treatment in the experimental setups at the rates between an average of 2-39 % and 5-27 %, respectively. The highest levels of bacterial activity and biofilm formation were mainly observed in the beach area (average rate +25 %) and marine industrial (average rate +19 %) sediments with microplastic contamination, respectively. Moreover, oxidative characteristics significantly linked the bacterial activities and biofilm formation. The oxidative indicators of Pseudomonas aeruginosa showed that catalase and glutathione reductase were more influenced by microplastic contamination of various sediments than superoxide dismutase activities. For instance, catalase and glutathione reductase activities were changed between -37 and +169 % and +137 to +144 %, respectively; however, the superoxide dismutase increased at a rate between +1 and + 21 %. This study confirmed that global warming as a consequence of climate change might influence the effect of microplastic on sediments regarding bacterial biochemical responses and oxidation characteristics.

Biomedical behaviors of CuO/γ-alumina/chitosan nanocomposites: Scolicidal and apoptotic effects on hydatid cysts protoscolices

Hydatid cysts caused by Echinococcus granulosus are a serious health problem that requires effective treatment. This study aimed to evaluate the scolicidal and apoptotic effects of copper oxide (CuO) and gamma alumina (γ-Al2O3) with or without chitosan (Chit), using Rosmarinus officinalis extract and chemical methods on protoscolices (PSCs) in vitro. The nanomaterials (NMs) were characterized by FTIR, EDS, DLS, XRD, FESEM, PDI, and zeta potential (ZP). Scolicidal and apoptotic effects of NMs were tested against PSCs at different concentrations and exposure times. The CuO NPs showed the highest scolicidal effect (33.26 %) among all NMs at 1.6 mg/mL and 60 min, followed by phytosynthesized CuO/γ-Al2O3 NC (23.41 %). The chitosan-modified CuO/γ-Al2O3 NC and the chemically synthesized CuO/γ-Al2O3 NC had less effect. The CuO NPs and the phytosynthesized CuO/γ-Al2O3 NC also significantly increased the expression of the caspase-3 gene in the PSCs at 0.4 mg/mL, indicating the induction of apoptosis. In conclusion, this study suggests that the phytosynthesized CuO/γ-Al2O3 NC and the CuO NPs could be potential candidates for treating echinococcosis by killing the PSCs through apoptosis. Further studies are needed to verify the in vivo efficacy and toxicity of these NMs and to optimize their delivery and targeting systems.

Fungal Secondary Metabolites/Dicationic Pyridinium Iodide Combinations in Combat against Multi-Drug Resistant Microorganisms

The spread of antibiotic-resistant opportunistic microbes is a huge socioeconomic burden and a growing concern for global public health. In the current study, two endophytic fungal strains were isolated from Mangifera Indica roots and identified as Aspergillus niger MT597434.1 and Trichoderma lixii KU324798.1. Secondary metabolites produced by A. niger and T. lixii were extracted and tested for their antimicrobial activity. The highest activity was noticed against Staphylococcus aureus and E. coli treated with A. niger and T. lixii secondary metabolites, respectively. A. niger crude extract was mainly composed of Pentadecanoic acid, 14-methyl-, methyl ester and 9-Octadecenoic acid (Z)-, methyl ester (26.66 and 18.01%, respectively), while T. lixii crude extract's major components were 2,4-Decadienal, (E,E) and 9-Octadecenoic acid (Z)-, and methyl ester (10.69 and 10.32%, respectively). Moreover, a comparative study between the fungal extracts and dicationic pyridinium iodide showed that the combination of A. niger and T. lixii secondary metabolites with dicationic pyridinium iodide compound showed a synergistic effect against Klebsiella pneumoniae. The combined formulae inhibited the bacterial growth after 4 to 6 h through cell wall breakage and cells deformation, with intracellular components leakage and increased ROS production.

Nanostructured γ-Al2O3 Synthesis Using an Arc Discharge Method and its Application as an Antibacterial Agent against XDR Bacteria

In the last few years, many efforts have been devoted to investigating the antibacterial activity of metal nanoparticles, especially against multidrug-resistant bacteria. Recently extensively drug-resistant (XDR) bacteria have emerged and caused a global threat. The purpose of this manuscript was to synthesize nanostructured γ-Al2O3 as an antibacterial agent against some XDRs. The results showed that Al2O3 was a mix of rod and spherical shapes in the nano range with diameters of less than 30 nm. The zeta potential was determined to estimate the surface charge for the synthesized γ-Al2O3, which was recorded as −34 ± 1.8 mV, indicating good stability. The synthesized nanostructured γ-Al2O3 showed a potent antibacterial activity against extensively drug-resistant Acinetobacter baumanii, with an inhibition zone diameter that reached 19 mm and a minimum inhibitory concentration (MIC) value that reached 2 µg/mL. The observed antibacterial activity of the prepared Al2O3 nanoparticles confirmed that the main mechanistic actions include bacterial cells apoptosis, ROS increment, cellular membrane disruption, and DNA damage. The cytotoxic effect (CC50) of the prepared γ-Al2O3-NPs was 1250 µg/mL in a normal human lung fibroblast cell line (WI-38 cells). It can be concluded that the synthesized γ-Al2O3 had an acceptable toxicity, which may pave the way for its use as a potent agent in the fight against XDR bacteria.

Nanoalumina triggers the antibiotic persistence of Escherichia coli through quorum sensing regulators lrsF and qseB

Nanomaterials with bactericidal effects might provide novel strategies against bacteria. However, some bacteria can survive despite the exposure to nanomaterials, which challenges the safety of antibacterial nanomaterials. Here, we used a high dose of antibiotics to kill the E. coli. that survived under different concentrations of nanoalumina treatment to screen persisters, and found that nanoalumina could significantly trigger persisters formation. Treatment with 50 mg/L nanoalumina for 4 h resulted in the formation of (0.084 ± 0.005) % persisters. Both reactive oxygen species (ROS) and toxin-antitoxin (TA) system were involved in persisters formation. Interestingly, RT-PCR analysis and knockout of the five genes related to ROS and TA confirmed that only hipB was associated with the formation of persisters, suggesting the involvement of other mechanisms. We further identified 73 differentially expressed genes by transcriptome sequencing and analyzed them with bioinformatics tools. We selected six candidate genes and verified that five of them closely related to quorum sensing (QS) that were involved in persisters formation, and further validated that the coexpression of QS factors lrsF and qseB was a novel pathway for persisters. Our findings provided a better understanding on the emergence of bacterial persistence and the microbial behavior under nanomaterials exposure.

A Mini Review of Antibacterial Properties of Al2O3 Nanoparticles

Bacterial antibiotic resistance is one of the most serious modern biomedical problems that prioritizes the search for new agents to combat bacterial pathogens. It is known that nanoparticles of many metals and metal oxides can have an antibacterial effect. However, the antibacterial efficacy of aluminum oxide nanoparticles has been studied little compared to the well-known antimicrobial properties of nanoparticles of oxides of metals such as zinc, silver, iron, and copper. In this review, we have focused on the experimental studies accumulated to date demonstrating the antibacterial effect of aluminum oxide nanoparticles. The review discusses the main ways of synthesis and modification of these nanoparticles, provides the proposed mechanisms of their antibacterial action against gram-positive and gram-negative bacteria, and also compares the antibacterial efficacy depending on morphological characteristics. We have also partially considered the activity of aluminum oxide nanoparticles against water microalgae and fungi. In general, a more detailed study of the antibacterial properties of aluminum oxide nanoparticles is of great interest due to their low toxicity to eukaryotic cells.

Degradation of subµ-sized bioplastics by clinically important bacteria under sediment and seawater conditions: Impact on the bacteria responses

In this study, we investigated the interaction of submicron-sized bioplastics with environmentally and clinically important bacteria under seawater and sediment conditions. To examine the relationship between submicron-sized bioplastics and bacteria in seawater and sediment, we focused on the bacterial activation and their biochemical key events toward the protein, carbohydrate, lipid, and antioxidant response. In addition, culture-dependent biofilm formation on submicron-sized bioplastics and their characterization was performed. The results indicated that selected bacteria increased their viability both in seawater and sediment with the submicron-sized bioplastics in that the bioplastics decreased their mass at the level of 10-23%. However, the activation level and mechanism affected the polymer type, bacteria, and environmental media, and submicron-sized bioplastics promoted biofilm formation with enhancing basophilic characteristics of biofilms.

Effects of ZnO nanoparticles on aerobic denitrifying bacteria Enterobacter cloacae strain HNR

The aerobic denitrification process is a promising and cost-effective alternative to the conventional nitrogen removal process. Widely used ZnO nanoparticles (NPs) will inevitably reach wastewater treatment plants, and cause adverse impacts on aerobic denitrification and nitrogen removal. Therefore, a full understanding of the responses and adaption of aerobic denitrifiers to ZnO NPs is essential to develop effective strategies to reduce adverse effects on wastewater treatment. In this study, the responses and adaption to ZnO NPs were investigated of a wild type strain (WT) and a resistant type strain (Re) of aerobic denitrifying bacteria Enterobacter cloacae strain HNR. When exposed to 0.75 mM ZnO NPs, the nitrate removal efficiency of Re was 11.2% higher than that of WT. To prevent ZnO NPs entering cells by adsorption, the production of extracellular polymeric substances (EPS) of WT and Re strains increased 13.2% and 43.9%, respectively. The upregulations of amino sugar and carbohydrate-related metabolism contributed to the increase of EPS production, and the increased nitrogen metabolism contributed to higher activities of nitrate and nitrite reductases. Interestingly, cationic antimicrobial peptide resistance contributed to resist Zn (II) released by ZnO NPs, and many antioxidative stress-related metabolism pathways were upregulated to resist the oxidative stress resulting from ZnO NPs. These findings will guide efforts to improve the aerobic denitrification process in an environment polluted by NPs, and promote the application of aerobic denitrification technologies.

Biofilm Formation of Clinically Important Bacteria on Bio-Based and Conventional Micro/Submicron-Sized Plastics

Micron/submicron-sized plastic debris in the environment is a global issue of increasing concern and may harm human health. A large number of studies have shown that plastic debris has various toxicological effects on different organisms. Thus, efforts have increased to replace conventional plastics with bioplastics. However, investigations on the relation of submicron-sized bioplastics- and conventional plastics to culture-dependent biofilm formation and their similarities and discrepancies are still very limited. For this purpose, two end products made from bioplastics and their equivalent end products from conventional plastics were used to examine the response of the biofilm formation of selected clinically important bacteria. To evaluate the similarities and differences of submicron-sized bioplastics and conventional plastics on biofilm formation, the physicochemistry (particle size, zeta potential, chemical composition, and surface chemistry) of the tested plastics was examined, as well as the characteristics of the biofilms (categorization, protein/carbohydrate).

Cytotoxic consequences of Halloysite nanotube/iron oxide nanocomposite and iron oxide nanoparticles upon interaction with bacterial, non-cancerous and cancerous cells

Cytotoxic effects of iron oxide (Fe₃O₄) nanoparticles and Halloysite nanotube/iron oxide (HNT/Fe₃O₄) nanocomposite are compared based on their interaction with Gram-negative bacteria Escherichia coli and Gram-positive bacteria Bacillus subtilis. Similarly, the action of these two nanomaterials on non-cancerous Vero cell lines and human lung cancerous (A-549) cell lines are compared. The cytotoxicity studies on Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite showed difference in the rate of killing of bacterial cells. This is reflected in differential cell growth, cell membrane integrity loss, lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production. These factors are measured over a range of concentrations of Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite and at specified time intervals, to test if there is any statistically significant difference between the toxicity of the two nanomaterials. Between the two nanomaterials, HNT/Fe₃O₄ nanocomposite is found to be less toxic to bacterial cells than Fe₃O₄ nanoparticles. HNT, when attached to the Fe₃O₄ nanoparticles, changes their surface characteristics and suppresses their inherent toxicity on bacteria. In the study on the effect on cell lines, Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite are both seen to be biocompatible with Vero cell lines. However, HNT/Fe₃O₄ nanocomposite showed more cytotoxicity than Fe₃O₄ nanoparticles on A-549 cell lines.

Antimicrobial Activity of Al₂O₃, CuO, Fe₃O₄, and ZnO Nanoparticles in Scope of Their Further Application in Cement-Based Building Materials

Nanoparticles were proposed as antibacterial cement admixtures for the production of cement-based composites. Nevertheless, the standards for evaluation of such admixtures still do not indicate which model organisms to use, particularly in regard to the further application of material. Apart from the known toxicity of nanomaterials, in the case of cement-based composites there are limitations associated with the mixing and dispersion of nanomaterials. Therefore, four nanooxides (Al₂O₃, CuO, Fe₃O₄, and ZnO) and seven microorganisms were tested to initially evaluate the applicability of nanooxides in relation to their further use in cement-based composites. Studies of nanoparticles included chemical analysis, microbial growth kinetics, 4- and 24 h toxicity, and biofilm formation assay. Nanooxides showed toxicity against microorganisms in the used concentration, although the populations were able to re-grow. Furthermore, the effect of action was variable even between strains from the same genus. The effect of nanoparticles on biofilms depended on the used strain. Gathered results show several problems that can occur while studying nanoparticles for specific further application. Proper protocols for nanomaterial dispersion prior the preparation of cement-based composites, as well as a standardized approach for their testing, are the fundamental issues that have to be resolved to produce efficient composites.

Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review

Engineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.