Antibacterial activity and possible mechanisms of one-step synthetic laminated flower-like nickelous(II) hydroxide

Hydrothermally synthesized biofunctional ceria nanoparticles using orange peel extract: optimization, characterization, and antibacterial and antioxidant properties

In this research, cerium oxide nanoparticles were synthesized using orange peel extract via a hydrothermal method. An equal ratio of orange peel extract to cerium nitrate salt led to the formation of cerium hydroxide carbonate, whereas a 1 : 10 ratio formed cerium oxide. The hydrothermal treatment was conducted for durations of 5 and 25 hours. Scanning electron microscopy (SEM) images revealed that the hydrothermal samples treated for 5 hours exhibited significant agglomeration in both extract to salt ratios after heat treatment. X-ray diffraction patterns confirmed that all samples were converted into cerium oxide after heating at 500 °C for 3 hours. Based on XRD and SEM results, three cerium oxide samples, including those synthesized through the 25 hours hydrothermal process with a 1 : 10 ratio and the 25 hours hydrothermal process with both ratios and subsequent heat treatment, were selected for further investigation. Fourier transform infrared (FT-IR) analysis revealed more adsorption of the functional groups of orange peel extract on the surface of the as-synthesized sample. Moreover, the heat-treated sample with a 1 : 10 ratio, initially cerium oxide, displayed a higher amount of surface functional groups than the one with a 1 : 1 ratio which was initially cerium hydroxide carbonate. The antibacterial activities of the samples were determined using the colony count method. Activities of all samples against Gram-negative bacteria are in the range of 91.5-93.2% with a negligible difference, whereas the as-synthesized sample exhibited a superior activity of 96.6 ± 1.8% against Gram-positive bacteria compared to the other two heat-treated samples. The 87.3% antioxidant activity of the as-synthesized sample significantly surpassed that of the other two samples, as evaluated by the DPPH radical scavenging method.

Mechanism and antibacterial synergies of poly(Dabco-BBAC) nanoparticles against multi-drug resistant Pseudomonas aeruginosa isolates from human burns

Multi-drug resistant bacteria are a major problem in the treatment of infectious diseases, such as pneumonia, meningitis, or even coronavirus disease 2019 (COVID-19). Cationic nanopolymers are a new type of antimicrobial agent with high efficiency. We synthesized and characterized cationic polymer based on 1,4-diazabicyclo [2.2.2] octane (DABCO) and Bis (bromoacetyl)cystamine (BBAC), named poly (DABCO-BBAC) nanoparticles(NPs), and produced 150 nm diameter NPs. The antibacterial activity of poly (DABCO-BBAC) against eight multi drug resistant (MDR) Pseudomonas aeruginosa isolates from human burns, its possible synergistic effect with gentamicin, and the mechanism of action were examined. Poly(DABCO-BBAC) could effectively inhibit and kill bacterial strains at a very low concentration calculated by minimum inhibitory concentration (MIC) assay. Nevertheless, its synergism index with gentamicin showed an indifferent effect. Moreover, transmission electron microscopy and lipid peroxidation assays showed that poly (DABCO-BBAC) distorted and damaged the bacterial cell wall. These results suggest that the poly (DABCO-BBAC) could be an effective antibacterial agent for MDR clinical pathogens.