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Multi-drug resistance to antibiotics represents a growing challenge in treating infectious diseases. Outside the hospital, bacteria with the multi-drug resistance (MDR) phenotype have an increased prevalence in anthropized environments, thus implying that chemical stresses, such as metals, hydrocarbons, organic compounds, etc., are the source of such resistance. There is a developing hypothesis regarding the role of metal contamination in terrestrial and aquatic environments as a selective agent in the proliferation of antibiotic resistance caused by the co-selection of antibiotic and metal resistance genes carried by transmissible plasmids and/or associated with transposons. Efflux pumps are also known to be involved in either antibiotic or metal resistance. In order to deal with these situations, microorganisms use an effective strategy that includes a range of expressions based on biochemical and genetic mechanisms. The data from numerous studies suggest that heavy metal contamination could affect the dissemination of antibiotic-resistant genes. Environmental pollution caused by anthropogenic activities could lead to mutagenesis based on the synergy between antibiotic efficacy and the acquired resistance mechanism under stressors. Moreover, the acquired resistance includes plasmid-encoded specific efflux pumps. Soil microbiomes have been reported as reservoirs of resistance genes that are available for exchange with pathogenic bacteria. Importantly, metal-contaminated soil is a selective agent that proliferates antibiotic resistance through efflux pumps. Thus, the use of multi-drug efflux pump inhibitors (EPIs) originating from natural plants or synthetic compounds is a promising approach for restoring the efficacy of existing antibiotics, even though they face a lot of challenges.

During the process of adapting to metal contamination, plants produce secondary metabolites that have the potential to modulate multidrug-resistant (MDR) phenotypes; this is achieved by inhibiting the activity of efflux pumps to reduce the minimum inhibitory concentrations (MICs) of antimicrobial substrates. Our study evaluated the effect of secondary metabolites of belowground parts of Pteris vittata L. and Fallopia japonica, two metal-tolerant plants from northern Vietnam, on six antibiotic-resistant Stenotrophomonas maltophilia strains possessing efflux pump resistance mechanisms that were isolated from soil and clinical samples. The chemical composition of aqueous and dichloromethane (DCM) fractions extracted from P. vittata and F. japonica was determined using UHPLC-DAD-ESI/QTOF analysis. The antibacterial and efflux pump inhibitory activities of the four fractions were evaluated for the six strains (K279a, 0366, BurA1, BurE1, PierC1, and 502) using a microdilution assay at fraction concentrations of 62.5, 125, and 250 μg/mL. The DCM fraction of F. japonica exhibited remarkable antibacterial activity against strain 0366, with a MIC of 31.25 μg/mL. Furthermore, this fraction also significantly decreased gentamicin MIC: four-fold and eight-fold reductions for BurA1 and BurE1 strains, respectively (when tested at 250 μg/mL), and two-fold and eight-fold reductions for K279a and BurE1 strains, respectively (when tested at 125 μg/mL). Pure emodin, the main component identified in the DCM fraction of F. japonica, and sennidine A&B only reduced by half the MIC of gentamicin (when tested at 30 μg/mL). Our results suggest that the DCM fraction components of F. japonica underground parts may be potential candidates for new bacterial efflux pump inhibitors (EPIs).

Marine microorganisms are an invaluable source of novel active secondary metabolites possessing various biological activities. In this study, the extraction and isolation of the marine sediment Penicillium species collected in Vietnam yielded ten secondary metabolites, including sporogen AO-1 (1), 3-indolecarbaldehyde (2), 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3), 2-[(2R-hydroxypropanoyl)amino]benzamide (4), 4-hydroxybenzandehyde (5), chrysogine (6), 3-acetyl-4-hydroxycinnoline (7), acid 1H-indole-3-acetic (8), cyclo (Tyr-Trp) (9), and 2’,3’-dihydrosorbicillin (10). Their structures were identified by the analysis of 1D and 2D NMR data. Among the isolated compounds, 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3) showed a strong inhibitory effect against Enterococcus faecalis with a minimum inhibitory concentration value of 32 µg/mL. Both 2-[(2R-hydroxypropanoyl)amino]benzamide (4) and 4-hydroxybenzandehyde (5) selectively inhibited E. coli with minimum inhibitory concentration values of 16 and 8 µg/mL, respectively. 2’,3’-Dihydrosorbicillin (10) potentially inhibited α-glucosidase activity at a concentration of 2.0 mM (66.31%).

We aimed to investigate the microbial diversity, mine lignocellulose-degrading enzymes/proteins, and analyze the domain structures of the mined enzymes/proteins in humus samples collected from the Cuc Phuong National Park, Vietnam. Using a high-throughput Illumina sequencer, 52 Gbs of microbial DNA were assembled in 2,611,883 contigs, from which 4,104,872 open reading frames (ORFs) were identified. Among the total microbiome analyzed, bacteria occupied 99.69%; the five ubiquitous bacterial phyla included Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, and Acidobacteria, which accounted for 92.59%. Proteobacteria (75.68%), the most dominant, was 5.77 folds higher than the second abundant phylum Bacteroidetes (13.11%). Considering the enzymes/proteins involved in lignocellulose degradation, 22,226 ORFs were obtained from the annotation analysis using a KEGG database. The estimated ratio of Proteobacteria/Bacteroidetes was approximately 1:1 for pretreatment and hemicellulases groups and 2.4:1 for cellulases. Furthermore, analysis of domain structures revealed their diversity in lignocellulose-degrading enzymes. CE and PL were two main families in pretreatment; GH1 and GH3-FN3 were the highest domains in the cellulase group, whereas GH2 and GH43 represented the hemicellulase group. These results validate that natural tropical forest soil could be considered as an important source to explore bacteria and novel enzymes/proteins for the degradation of lignocellulose.

A cubic Bézier-profile plate for multimodal vibration energy harvesting was developed. The design of the plate was based on an optimization procedure in which the profile of the plate was optimized via the parameters of a cubic Bézier curve to meet the requirements. The multimodal energy harvesting of the plate exploited its first bending mode and its first twisting mode. The conversion of vibration energy into electrical energy was by electromagnetic induction with a magnet attached to a corner of the plate. These two closely spaced vibration modes achieved the multi-modal energy harvesting of the device. Prototypes of the device were manufactured using a numerical-control machining process. The experimental results were in good agreement with the design specifications. With the same base lengths, height, and thickness, the maximum von Mises stress of the proposed plate was much lower due to its bell-shaped profile. The cubic Bézier curve chosen for the plate profile was effective for design of the closely-spaced multimodal vibration energy harvester. With the flexibility of its controllable parametric curve, a high design freedom of the energy harvester with specified frequency ratios could be achieved.

The smoothing ball-burnishing process has commonly been used as a post-processing method to reduce the irregularities of machined surfaces. However, the mechanism of this process has rarely been examined. In this study, a simulation procedure is proposed to predict the surface roughness of a burnished workpiece under varying burnishing forces. The roughness of the workpiece surface was firstly approximated by parabolic functions. The burnishing process was then numerically simulated through two steps, namely the elastic–plastic indentation of the burnishing ball on the workpiece’s surface, and the sliding movement of the burnishing tool. The results of the simulation were verified by conducting small ball-burnishing experiments on oxygen-free copper (OFC) and Polmax materials using a load cell-embedded small ball-burnishing tool. For the OFC material, the optimal burnishing force was 3 N. The obtained experimental surface roughness was 0.18 μm, and the simulated roughness value was 0.14 μm. For the Polmax material, when the burnishing force was set at its optimal value—12 N, the best experimental and simulated surface roughness were 0.12 μm and 0.10 μm, respectively.