Search Results (971)

Wastewater treatment plants (WWTPs) are important interfaces for the persistence and dissemination of antimicrobial resistance genes (ARGs) in the environment. This study investigated colistin resistance and the presence of mobile colistin resistance (mcr) genes in Enterobacterales isolated from a poultry slaughterhouse WWTP in Brazil. Samples were collected from raw sewage, an equalization tank, and treated effluent. A total of 27 Enterobacter spp. isolates were identified, of which 70.4% showed resistance to colistin (MIC range: 2 to ≥512 mg/L). PCR screening detected mcr-1 in two isolates and mcr-10 in three isolates distributed across all treatment stages, including the final effluent. Whole-genome sequencing of a representative isolate from treated effluent identified Enterobacter vonholyi ST3343, carrying a plasmid-borne mcr-10 gene on an ~107 kb IncFII(Yp) plasmid, along with additional resistance determinants. Phylogenetic analysis supported the classification of this gene as a novel allele, mcr-10.6. The persistence of a clonal lineage harboring mcr-10.6 throughout the treatment system indicates that conventional wastewater treatment may not effectively eliminate clinically relevant ARGs. These findings highlight treated effluent as a potential route for environmental dissemination of colistin resistance and reinforce the need for improved monitoring and mitigation strategies within a One Health framework. Full article

Background: Acinetobacter baumannii (A. baumannii) is a critical-priority pathogen of major concern in healthcare settings. Colistin remains a last-resort antibiotic for multidrug-resistant (MDR) A. baumannii infections; however, resistance is increasingly reported worldwide yet remains understudied in Bahrain. Reliable detection methods and understanding clonal dissemination are essential for infection control. Objectives: This study aimed to (1) determine the rate of colistin resistance in 102 clinical A. baumannii isolates from Bahrain, (2) evaluate the diagnostic performance of the colistin agar test (CAT) and E-test against broth microdilution (BMD method), and (3) assess clonal relationships using BOX-PCR fingerprinting. Methods: 102 clinical isolates from multiple hospitals in Bahrain underwent susceptibility testing via the BMD method, CAT, and E-test; screening for mcr-1 to mcr-5 genes; and BOX-PCR DNA fingerprinting. Results: Colistin resistance was detected in 14.7% of isolates by BMD method, higher than regional and global averages. All resistant isolates were mcr-negative, suggesting chromosomally mediated resistance. CAT showed 86.7% sensitivity, 98.8% specificity, and a 13.3% very major error rate. The E-test failed to detect resistant isolates (very major error 100%). BOX-PCR revealed predominant clonal relatedness with intra- and inter-hospital spread. Conclusions: Colistin resistance in A. baumannii from Bahrain exceeds regional and global levels, likely driven by chromosomal mechanisms under selective pressure. The BMD method remains the gold standard for colistin testing, while CAT may serve as a screening tool requiring confirmation. Strengthened stewardship and infection control measures are vital to contain dissemination. Full article

Anaerobic biodegradation is the most affordable method for the degradation of N,N-dimethylformamide. However, the degradation efficiency depends on the concentration. To elucidate the responses of microbial community to N,N-dimethylformamide load, microbial diversity, composition and functional changes at different concentrations of 100, 2000, and 3500 mg/L were analyzed. Results showed that as the N,N-dimethylformamide influent concentration increased from 100 to 2000 mg/L, the removal rate stabilized at 90%, whereas it decreased to ~75% at concentrations over 2000 mg/L. Microbial community diversity increased, and specialists were enriched at 3500 mg/L. Patescibacteria (42.88% and 42.90%), Bacillota (18.52% and 18.54%), and Pseudomonadota (7.13% and 7.09%) were the dominant phyla at 100 mg/L and 2000 mg/L, respectively, and Patescibacteria (16.88%) and Pseudomonadota (15.34%) were the dominant phyla at 3500 mg/L. Methylotrophic methanogeneic (Methanolobus and Methanomassiliicoccus) and syntrophic electron-donating bacteria (Clostridiumand and Trichococcus) were significantly enriched. DMF-degrading genes (fdh, rfA/nrfH, and ATPase) and methylotrophic methanogenesis genes (mcr, mta, and mtm) were significantly upregulated. Therefore, the degradation of N,N-dimethylformamide was characterized by a parallel carbon flux distribution, “methylamine-driven methanogenesis + further oxidation/integration of single-carbon intermediates”, and the nitrogen flux tended to enter a reductive nitrogen cycle characterized by retention and reuse. Full article

Antimicrobial resistance in companion animals is a growing public health concern, yet data on last-resort resistance genes in clinical canine isolates remain scarce. This study characterizes the molecular distribution of critical resistance determinants, including mcr variants (1–5), in bacteria isolated from canine otitis externa in Ankara, Turkey. Using a combination of phenotypic disk diffusion and targeted quantitative polymerase chain reaction (qPCR), we identified Enterobacter spp., Staphylococcus spp., and Pseudomonas aeruginosa as the predominant pathogens. Notably, among Gram-negative isolates (n = 9), our results indicate preliminary evidence of mobile colistin resistance genes, particularly mcr-3 in 44.4% (4/9), and mcr-4 and mcr-5 each in 33.3% (3/9), marking the first report of these variants in canine ear infections within an urban environment. The observed notable discrepancies between genotypic carriage and phenotypic expression suggest the possible presence of silent resistance reservoirs that traditional diagnostics may overlook. These findings underscore the urgent need for molecular-integrated surveillance in veterinary clinical practice to prevent the zoonotic spread of last-resort resistance genes and to safeguard both animal and public health under the ‘One Health’ framework. Full article

Mitigating methane (CH₄) emissions from paddy fields without compromising yield remains a critical challenge for sustainable agriculture, primarily due to trade-offs between emission reduction and nutrient availability. Biochar-based fertilizer (BF), which integrates biochar with mineral nutrients, may address this constraint by regulating carbon and nitrogen availability. This study evaluated the effects of biochar-based fertilization on CH₄ emissions and rice productivity. A one-season field experiment was conducted in Hydragric Anthrosols with four treatments: no fertilization (control), conventional chemical fertilization (CF), integrated application of biochar-based and chemical fertilizers (CBF), and biochar-based fertilizer alone (BF). Methane fluxes were monitored alongside soil physicochemical properties and the abundances of key functional microbial genes. Compared with CF, BF significantly reduced cumulative CH₄ emissions by 23.24% while maintaining comparable rice yield, resulting in a 28.67% reduction in yield-scaled CH₄ emissions. Biochar-based fertilization decreased dissolved organic carbon availability, buffered NH₄⁺-N concentrations, and increased soil pH. These changes shifted the microbial balance of CH₄ cycling, suppressing methanogenesis and enhancing methane oxidation, as reflected by a lower mcrA/pmoA ratio. Structural equation modeling indicated that CH₄ mitigation was jointly driven by reduced methanogenic activity and enhanced methane oxidation. Overall, biochar-based fertilization regulates soil chemical and microbial processes to mitigate CH₄ emissions without yield penalties, demonstrating strong potential as a scalable and field-applicable strategy for low-carbon rice production. Full article

The morphological structure and connectivity of river systems are critical to ecological functions, water resource allocation, and disaster prevention in watersheds. This study applies an integrated approach combining morphological analysis, graph theory, landscape ecology, and complex network theory to analyze and optimize the river network structure of the Baiyangdian basin. The results showed significant structural improvements from 2014 to 2025: river network density (Dr) increased from 0.0335 to 0.1443 km/km², and river frequency (Fr) rose from 0.0015 to 0.0132 rivers/km². Connectivity indices also exhibited an overall increasing trend: circuitry (α) increased from −0.05 to 0.03, the edge–node ratio (β) from 0.90 to 1.06, and network connectivity (γ) from 0.30 to 0.35. Spatial analysis further identified a clear gradient of node importance: peripheral nodes showed low centrality, while critical nodes were predominantly concentrated along the South-to-North Water Diversion Project (SNWD) corridor. Optimization based on the 2025 baseline further improved network connectivity, with corresponding increases in connectivity metrics. These findings provide scientific support for integrated water management and climate-adaptive planning in the Baiyangdian basin. Full article

The high penetration of distributed photovoltaic (PV) systems introduces significant voltage fluctuations in distribution networks due to the stochastic nature of PV generation. To address the limitations of conventional volt–var regulation, this paper proposes a novel two-layer hierarchical framework driven by two core innovations: a robust globally scheduled magnetically controlled reactor (MCR) and an autonomous adaptive control strategy for local PV inverters. At the local layer, an adaptive five-region weighting strategy enables PV inverters to rapidly mitigate minor voltage fluctuations without relying on communication networks. At the global layer, an improved particle swarm optimization (IPSO) algorithm is employed to coordinate MCR reactive power scheduling, thereby mitigating severe voltage violations and reducing active power losses. The proposed framework is validated on a modified IEEE 33-bus distribution system. Simulation results show that the adaptive local control of PV inverters effectively reduces node voltage deviations compared with conventional control methods. Furthermore, the two-layer coordinated optimization significantly improves overall system performance by reducing both the objective function value and the maximum voltage deviation compared with single-layer control strategies. Compared with other optimization algorithms, IPSO demonstrates strong robustness and stable convergence in the proposed optimization problem. Overall, the proposed hierarchical framework provides a reliable, scalable, and cost-effective solution for real-time voltage regulation in modern active distribution networks. Full article

The in-service assessment of marine propulsion engines requires more than nominal rating comparison because operating severity is shaped by propeller demand, resistance growth, air-path response, and thermal state. This study develops a quantitative benchmarking method for the regime-dependent performance assessment of a low-speed two-stroke Wärtsilä 6RT-flex58T-D engine installed on a 31,000 DWT multi-purpose container vessel. The method integrates certified sea-trial measurements, endurance-test records, manufacturer load-diagram constraints, and a 15% service-margin projection within one reference framework. Three representative regimes are evaluated: a measured light-running baseline (SR1), a measured thermally stabilised sustained regime (SR2), and a projected heavy-running regime derived from the baseline using a 15% sea-margin assumption (R2). Comparison is performed using indicators of operating-point position, shaft torque, propeller-law consistency, selected air-path and thermal variables, load-diagram proximity, and corrected specific fuel oil consumption where available. The SR1 baseline followed the fitted propeller law with deviations not exceeding 1.18%, confirming a coherent light-running reference. In SR2, corrected SFOC decreased from 174.4 to 172.0 g/kWh, while the exhaust temperature before turbine increased from 359 °C to 435 °C, and the corresponding thermal margin decreased from 156 °C to 80 °C. Under the +15% service-margin projection, the required shaft power at the 100% trial point increased from 12,046.0 to 13,852.9 kW, exceeding the 13,560 kW installation MCR by 2.2%, with corresponding 15% increases in torque and BMEP. These results demonstrate that measured baseline operation, sustained-load severity, and projected heavy-running demand can be distinguished quantitatively within one installation-specific load-diagram-based benchmarking framework. Full article

Background/Objectives: Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major nosocomial pathogen. Although newer agents have reduced colistin use in high-income countries, this polymyxin remains important in many low- and middle-income settings. Colistin resistance in K. pneumoniae is most commonly associated with chromosomal alterations affecting the MgrB–PhoPQ pathway, or with plasmid-mediated mcr genes. This study aimed to investigate chromosomally mediated colistin resistance in CRKP clinical isolates from a Tunisian tertiary hospital. Methods: Between 2010 and 2015, 317 non-duplicate CRKP isolates were collected at Charles Nicolle Hospital, Tunis. Colistin MICs were determined by broth microdilution. Phenotypic tests and PCR characterized carbapenemases, extended-spectrum β-lactamases, AmpC, plasmid-mediated quinolone resistance, mcr and virulence genes. Porins (OmpK35/OmpK36) and the mgrB, phoP and phoQ loci were analyzed by SDS-PAGE and sequencing. Clonal relatedness was assessed by ERIC-PCR and multilocus sequence typing. We additionally compared colistin-resistant isolates with a panel of colistin-susceptible CRKP controls and assessed phenotypic stability after serial passages without colistin. Results: Five isolates (1.6%) were colistin-resistant. All were multidrug-resistant, produced OXA-48, and two also carried NDM-1. The isolates belonged to five distinct sequence types, including high-risk clones (ST11, ST101, ST147). No mcr genes were detected. Four isolates carried disruptive mutations in mgrB, and the remaining strain harbored inactivating mutations in both phoP and phoQ with an intact mgrB. Truncating alterations in PhoP/PhoQ and frequent loss or truncation of OmpK35/OmpK36 were observed. No mgrB/phoP/phoQ alterations were detected among colistin-susceptible controls, and colistin MICs remained stable after 7 days of drug-free passaging. Conclusions: In Tunisian CRKP, colistin resistance was associated with chromosomal alterations, predominantly involving disruption of the MgrB–PhoPQ pathway, in the absence of mcr genes. These mechanisms in both high-risk and emerging sequence types underscore the adaptability of CRKP and the need for surveillance where colistin remains an important therapeutic option. Full article

Multivariate calibration methods have proven to be helpful in interpreting complex spectral data, particularly in the simultaneous analysis of pharmaceutical mixtures. In this study, three chemometric-assisted spectrophotometric methods were developed and validated for the simultaneous assessment of flunixin meglumine (FM) and florfenicol (FF), namely, multivariate curve resolution–alternating least squares (MCR-ALS), artificial neural networks (ANNs), and partial least squares (PLS). These methods were successfully utilized to address the significant spectral overlap between FM and FF in their combined dose form, enabling simultaneous quantification without prior chromatographic separation. Statistical analysis was conducted to compare the performance of the proposed methods to that of a published HPLC method, and the results showed no significant variation in trueness or precision. The proposed methods were validated according to ICH guidelines, showing high sensitivity, low LOD and LOQ, and excellent precision (%RSD < 2.0%). Furthermore, they were evaluated for environmental sustainability using the analytical greenness (AGREE) metric and the complex modified green analytical procedure index (Complex MoGAPI), which provided a greenness score of 0.7 and a total sustainability score of 80. These results demonstrate the applicability of the proposed chemometric methods as straightforward, effective, and ecologically beneficial substitutes for regular quality control analysis. Full article

Ecological networks provide an important spatial framework for maintaining regional ecological security in fragmented landscapes. However, structural comparison of ecological network evolution at the provincial scale remains relatively limited, especially in cold-region contexts. Taking Heilongjiang Province in Northeast China as the study area, this study applies a structure-oriented workflow integrating ecological sensitivity assessment, the Minimum Cumulative Resistance (MCR) model, and edge-betweenness-based backbone corridor extraction to examine ecological network change in 2000, 2010, and 2020. The results show that 16, 18, and 17 ecological source areas were identified in 2000, 2010, and 2020, respectively, with a relatively stable spatial distribution concentrated in forest- and wetland-dominated regions. The total length of potential ecological corridors decreased from 12,634 km in 2000 to 11,985 km in 2020. Quantitative topological indicators further indicate that the 2010 ecological network was the most compact and densely connected of the three periods, whereas the 2020 network remained connected but exhibited lower structural compactness. Backbone ecological corridors retained only a limited proportion of the full corridor network while preserving overall connectivity, indicating that a relatively small subset of structurally important corridors supported the main network framework. Spatially, structural weakening was more evident in the Harbin–Daqing region, whereas the northwestern and southeastern parts of the province maintained relatively stable ecological foundations. These patterns were broadly consistent with land-use dynamics, particularly grassland decline and built-up land expansion. Overall, this study provides an applied structure-oriented workflow for examining ecological network evolution at the provincial scale and offers a spatial basis for ecological conservation and territorial planning in cold-region provinces. Full article

Background/Objectives: Freshwater microalgae–bacteria consortia are increasingly utilized in wastewater treatment and biomass production. However, bacteria associated with the algal phycosphere may act as environmental reservoirs of multidrug-resistant (MDR) phenotypes and antibiotic resistance genes (ARGs), including resistance to last-resort antibiotics such as colistin. Methods: An axenic culture of the freshwater microalga Pectinodesmus pectinatus was established using a NaClO-based cleaning protocol. Three phycosphere-associated bacterial strains (Chryseobacterium sp., Pseudomonas monteilii, and Stenotrophomonas pavanii) were isolated and identified by 16S rRNA gene analysis. Antimicrobial susceptibility testing was performed using broth microdilution against 16 antibiotics. Whole-genome sequencing of the most resistant isolate, S. pavanii, was conducted using Oxford Nanopore technology, followed by genome annotation and in silico resistome analysis using CARD, AMRFinderPlus, and ResFinder. Results: Among the three isolates, S. pavanii exhibited the broadest resistance profile, including high minimum inhibitory concentrations (MICs) to multiple β-lactams and colistin (MIC ≥ 16 μg/mL). No plasmid-borne mcr genes were detected. Instead, the genome encoded multiple chromosomal determinants potentially associated with polymyxin non-susceptibility, including lipid A and lipopolysaccharide modification pathways (e.g., arn genes and eptA), outer-membrane maintenance and LPS transport systems, multidrug efflux pumps, and regulatory elements. Integration of genomic and phenotypic data suggested that the observed colistin non-susceptibility may be associated with intrinsic chromosomal determinants inferred from whole-genome analysis. Conclusions: This study demonstrates that the P. pectinatus phycosphere can harbor multidrug-resistant (MDR) bacteria, including strains exhibiting colistin non-susceptibility potentially associated with a repertoire of intrinsic chromosomal resistance mechanisms inferred from genomic analysis. Therefore, freshwater microalgae-based systems should be considered potential environmental reservoirs contributing to the dissemination of antimicrobial resistance. Full article

The rise in antimicrobial resistance represents a significant challenge to global health. The reason partially lies in an inappropriate use of conventional antibiotics and the subsequent rapid spread of multidrug-resistant pathogen strains. This emergency requires an urgent search for conceptually new antimicrobial agents. A viable alternative to conventional antibiotics is antimicrobial peptides (AMPs), which are ribosomally synthesized molecules with considerable potential as next-generation anti-infectious therapeutics. Previously, we have reported on the β-hairpin peptide Ap9, an analog of abarenicin from the marine polychaeta Abarenicola pacifica, with potent activity against key Gram-negative pathogens. Here, it is shown that Ap9 acts in a manner resembling polymyxin B, namely via interaction with lipopolysaccharide (LPS), and retains its activity against polymyxin-resistant isolates without observed cross-resistance, and causes insignificant damage in cytoplasmic membrane at bactericidal concentrations. NMR spectroscopy reveals that LPS binding induces a conformational rearrangement of Ap9, its dimer formation, and local structural remodeling of the peptide region (residues 8–12) into 3₁₀-helix. Bacterial resistance to Ap9 was found to be relatively low with a reduced susceptibility associated with infrequent genetic alterations, such as the mutation in lptD or the deletion in mlaA. Furthermore, Ap9 demonstrates a favorable tolerability, a wider therapeutic window than that of polymyxin B, and a sufficiently long half-life through the systemic use, as well as in vivo efficacy in murine models of Gram-negative infections, including sepsis caused by the mcr-1-harboring Escherichia coli strain. The obtained results point to Ap9 as a promising candidate for further preclinical studies aimed at development of an alternative to polymyxins. Full article

The northeastern margin of the Qinghai–Tibet Plateau is an ecologically fragile region that faces severe habitat fragmentation, which directly threatens regional biodiversity conservation and ecological security. To address this challenge, this study constructed a hierarchical “source-corridor-node” ecological network for the Gannan Tibetan Autonomous Prefecture by integrating Morphological Spatial Pattern Analysis (MSPA), the Minimum Cumulative Resistance (MCR) model, landscape connectivity assessment, and gravity modeling. The key results are as follows: (1) The Gannan Yellow River Water Source Replenishment Area contains 11 core ecological source regions, which are predominantly located in the southeastern regions of Diebu County and Zhouqu County, covering a total area of 4237.81 km²; (2) Ecological resistance analysis identifies high-resistance zones concentrated in anthropogenically active river valleys and urban belts (e.g., Hezuo urban area, Awanzang Town, and the G213 corridor). Low-resistance zones are predominantly situated in protected ecological enclaves (e.g., Zhagana Geopark and Gahai Wetland Reserve); (3) A total of 55 ecological corridors were identified, with a total length of 4355.77 km. Among these, 26 were classified as key ecological corridors, primarily distributed in Diebu and Zhouqu counties in the eastern part of Gannan Prefecture. These areas feature relatively concentrated ecological sources, and the key corridors play a critical role in connecting isolated ecological patches and maintaining regional ecological connectivity. (4) Across the entire territory of Gannan Prefecture, a total of 81 first-level ecological nodes and 53 second-level ecological nodes were delineated. As the core hub of the regional ecological network in Gannan Prefecture, Diebu County encompasses 60 First-level and 41 Second-level ecological nodes, respectively. The hierarchical “source-corridor-node” ecological network constructed in this study effectively enhances the overall landscape connectivity of the area. This progressive analytical framework—integrating source identification, corridor extraction, and node diagnosis—provides a scientific basis for biodiversity conservation, territorial ecological restoration, and sustainable development in high-altitude ecologically fragile zones. Full article

Background/Objectives: The emergence of antimicrobial-resistant (AMR) pathogens in aquaculture ecosystems poses a significant risk to both food security and human health. Shewanella species are recognized as significant AMR reservoirs, yet their prevalence and resistance mechanisms within a shrimp-related ecosystem remain poorly characterized. This study aimed to perform a genotypic and phenotypic characterization of S. algae VK101, isolated from wild-caught black tiger shrimp (Penaeus monodon) broodstock. Methods: A complete 5.21 Mb genome was generated using a hybrid Illumina and Oxford Nanopore sequencing approach. Antimicrobial susceptibility was evaluated for 21 antibiotics via Minimum Inhibitory Concentration (MIC) testing. Comparative pangenomics and genome-wide association studies (GWAS) across 125 S. algae genomes were conducted to identify novel resistance determinants. Results: MIC analysis revealed that VK101 was resistant to ampicillin (>16 µg/mL) and colistin (8 µg/mL), while showing intermediate susceptibility to imipenem and ciprofloxacin. In silico analysis identified 205 antimicrobial resistance genes (ARGs), including a perfect hit for the fluoroquinolone resistance gene qnrA3. Notably, no mcr genes were detected. Although VK101 exhibited moderate resistance (8 µg/mL), GWAS across the broader S. algae population linked a specific lptA mutation (K140N) to high-level resistance (64 µg/mL). Other GWAS-identified genes (e.g., czcA, ampC, and oprM) likely represent indirect associations driven by genetic linkage or clade-specific markers rather than direct causal factors. Conclusions: These findings highlighted the presence of multidrug-resistant S. algae in wild-caught P. monodon broodstock, reflecting the occurrence of antimicrobial resistance in aquatic environments. Colistin resistance in these isolates was primarily mediated by chromosomal variants rather than mobile mcr elements, indicating the need for integrated genomic surveillance within the aquaculture value chain. Full article