Microorganisms play an important role in maintaining the proper functioning of river ecosystems and are promising candidates for environmental indicators. They are also highly sensitive to environmental changes. It is necessary to have basic knowledge about them in order to know the ecological status of river ecosystem. To our knowglege, there is very little information on the status of microorganisms in surface water of the Seine River, although the Seine River is one of the rivers that suffers the greatest impact from humain activities in the world due to a weak dilution effect. It is therefore necessary to carry out a microbial analysis to assess the ecological status of the Seine River and to use it as a reference to compare with the future state when, for instance, new disinfection technologies of wastewater are implemented.

Background: Klebsiella pneumoniae is a dangerous pathogen, responsible for a variety of infections and has been growing resistance to antibiotics, making it difficult to treat diseases caused by this bacterium. A better understanding of the phenotypic and genotypic characteristics of this bacterium is essential for developing more effective treatments. This study examines the prevalence of Klebsiella pneumoniae in patient samples from eight hospitals in Ho Chi Minh City, Vietnam, in 2023, focusing on its AmpC β-lactamase, ESBL, and carbapenemase genotypes. Methods and Results: A total of 230 Klebsiella pneumoniae strains were isolated from clinical specimens, including sputum, pus, urine, bronchial lavage fluid, blood, and other fluids. The disk diffusion method detected the presence of these resistance enzymes, while multiplex real-time PCR identified the associated genes. Results showed that 78.7% of isolates produced AmpC β-lactamase, 21.3% produced ESBL, and 27.0% produced carbapenemase. ESBL-producing strains (90.9%) were more common than AmpC (67.4%) and carbapenemase (45.7%) strains. Additionally, 27.0% of isolates produced multiple resistance enzymes. The most prevalent AmpC gene was DHA (63.5%), while SHV (84.3%), TEM (55.2%), and CTX-M (70.0%) were the most common ESBL genes. OXA-48 (31.3%) was the dominant carbapenemase gene, followed by NDM1 (24.8%) and KPC (9.1%). On average, each strain carried 3.3 resistance genes. Conclusions: This study reveals a high prevalence of antimicrobial resistance in Klebsiella pneumoniae isolates from patient samples in Ho Chi Minh City hospitals, notably to third-generation cephalosporins and carbapenems. These findings highlight the need for ongoing surveillance and improved treatment strategies.

Diverse microbial communities play a crucial role in maintaining the proper functioning of river ecosystems and are considered important indicators of river water quality. Although the Seine River being heavily impacted by human activities, little is known about the microbial communities in its surface waters. In order to monitor water quality and promote sustainable use, we studied its microbial diversity using high-throughput sequencing technology, and explored their relationships with physico-chemical properties. The dominant phyla identified were Proteobacteria, Actinobacteriota, Bacteriodota, and Cyanobacteria. The presence of the Alphaproteobacteria and Gammaproteobacteria indicates that the Seine River water nutrient profile is mainly determined by the recalcitrant organic compounds present in WWTP effluents. Bacterial diversity showed significant temporal variability with a highly significant difference in bacterial composition between 2020 and 2021, probably due to variations in water flow favoring Cyanobacteria growth. Summer displayed higher microbial activity and abundance than autumn, attributed to temperature and orthophosphate content. Spatial variation in bacterial composition was observed between sites upstream and downstream of Paris, as well as before and after of the Seine Valenton-WWTP, subject to an accumulation phenomenon and impacted by wastewater treatment. Further assessment of emerging contaminants and other pollutants is required to better understand these variations. These results provide a basic understanding of the microbial community in the Seine River, serving as a reference for assessing the impact of implementing new wastewater disinfection techniques in the near future. Graphical abstract

Poorly-treated wastewater harbors harmful microorganisms, posing risks to both the environment and public health. To mitigate this, it is essential to implement robust disinfection techniques in wastewater treatment plants. The use of performic acid (PFA) oxidation has emerged as a promising alternative, due to its powerful disinfection properties and minimal environmental footprint. While PFA has been used to inactivate certain microbial indicators, its potential to tackle the entire microbial community in effluents, particularly resistant bacterial strains, remains largely unexplored. The present study evaluates the efficacy of PFA disinfection on the microbial communities of a WWTP effluent, through microbial resistance mechanisms due to their membrane structure. The effluent microbiome was quantified and identified. The results showed that the number of damaged cells increases with CT, reaching a maximum for CT = 240 mg/L•min and plateauing around 60 mg/L•min, highlighting the optimal conditions for PFA-disinfection against microbial viability. A low PFA level with a 10-min contact time significantly affected the microbial composition. It is worth noting the sensitivity of several bacterial genera such as Flavobacterium, Pedobacter, Massilia, Exiguobacterium, and Sphingorhabdus to PFA, while others, Acinetobacter, Leucobacter, Thiothrix, Paracoccus, and Cloacibacterium, showed resistance. The results detail the resistance and sensitivity of bacterial groups to PFA, correlated with their Gram-positive or Gram-negative membrane structure. These results underline PFA effectiveness in reducing microbial levels and remodeling bacterial composition, even with minimal concentrations and short contact times, demonstrating its suitability for widespread application in WWTPs.

Introduction. Carbapenem-resistant Acinetobacter baumannii (CRAB) represents a critical healthcare threat with limited treatment options, particularly challenging in Southeast Asia where resistance rates exceed 65%. Hypothesis/Gap Statement. Current synergy testing methods are labour-intensive and poorly standardized, limiting their clinical application. We hypothesize that synergistic interactions between antibiotics follow predictable mathematical patterns derivable from separate MIC determinations for each antibiotic. Aim. To evaluate the efficacy of colistin-meropenem-ampicillin/sulbactam combinations at standard dosages and develop a predictive mathematical model for synergistic interactions against CRAB. Methodology. A cross-sectional study was conducted using 61 CRAB clinical isolates from a Vietnamese tertiary hospital. MICs were determined using broth microdilution, and synergy was assessed via checkerboard assays. Mathematical models were developed to predict fractional inhibitory concentration (FIC) values from separate MIC determinations for each antibiotic. Results. All isolates demonstrated high-level meropenem resistance (MICs 32-≥128 µg ml ⁻¹ ) and ampicillin/sulbactam resistance (98.4% with MICs≥64/32 µg ml ⁻¹ ) but remained intermediate to colistin (MICs 0.0625–0.25 µg ml ⁻¹ ). The triple combination achieved 100% synergy at standard ampicillin/sulbactam doses (8/4 µg ml ⁻¹ ). Our log-transformed power model accurately predicted synergistic interactions ( R ²=0.928) using the equation log(FIC) = −2.52+(−1.02) × 1/√Mero+0.43×1/√Col+4.32×1/√As. Conclusion. The triple combination achieves universal synergy at standard dosages, potentially reducing toxicity risks. Our mathematical model enables rapid prediction of effective combinations from routine susceptibility tests, offering a transformative approach to optimizing therapy against multidrug-resistant pathogens.

Background: Acinetobacter baumannii has emerged as an important opportunistic pathogen due to its increasing resistance to carbapenems, which severely limits therapeutic options. This study is aimed at characterizing the phenotypic resistance profiles and distribution of carbapenemase‐encoding genes among clinical A. baumannii isolates collected from a tertiary‐care hospital in southern Vietnam. Methods: A retrospective study was conducted on 156 A. baumannii isolates collected at the University Medical Center Ho Chi Minh City between January and December 2024. Antimicrobial susceptibility testing was performed using the BD Phoenix M50 system. Carbapenemase‐encoding genes, including bla OXA‐23, bla OXA‐58, bla NDM‐1, and bla KPC, were detected using multiplex real‐time PCR. Results: Among the 156 isolates, 70.51% were identified as carbapenem‐resistant A. baumannii (CRAB). Most CRAB isolates originated from respiratory specimens (83.64%) and intensive care units (60%). CRAB isolates exhibited extensive multidrug resistance, with resistance rates ranging from 76% to > 96% for most cephalosporins, fluoroquinolones, and aminoglycosides. In contrast, minocycline retained the highest in vitro activity, with a resistance rate of only 10%. The most prevalent carbapenemase gene was bla OXA‐23 (73.6%), followed by bla NDM‐1 (52.7%) and bla OXA‐58 (20.0%). Overall, 95.45% of CRAB isolates were phenotypically identified as carbapenemase‐producing A. baumannii (CP‐AB). The co‐occurrence of bla OXA‐23 and bla NDM‐1 was the most common gene combination, detected in 23.64% of CRAB isolates. Conclusion: This study demonstrates a high burden of CRAB in a Vietnamese tertiary hospital, largely driven by the co‐existence of bla OXA‐23 and bla NDM‐1. The identification of carbapenem‐resistant isolates lacking phenotypic carbapenemase activity suggests the involvement of alternative, nonenzymatic resistance mechanisms. Continuous molecular surveillance and strengthened antimicrobial stewardship are urgently needed to limit CRAB dissemination in Vietnam.