Frontiers in Microbiology最新文献

Background and objective: Brucellosis is a common zoonotic disease worldwide. Because its symptoms are non-specific and laboratory findings vary, diagnosis remains challenging. Blood culture is still the gold standard for confirmation, but its yield is often limited. This study aimed to estimate blood-culture positivity among hospitalized male patients with newly diagnosed brucellosis and to identify clinical and laboratory factors independently associated with culture positivity within confirmed cases.

Methods: We conducted a hospital-based retrospective study of 1,188 hospitalized men with newly diagnosed brucellosis admitted to a tertiary infectious-disease hospital in China between 2021 and 2023. Demographics, clinical manifestations, laboratory parameters, and blood-culture results were collected. Multivariate logistic regression was used to identify independent predictors of a positive blood culture.

Results: The overall blood-culture positivity rate was 30.9%. Univariate analysis indicated that disease stage, fatigue, fever, anorexia, splenomegaly, arthritis, paraspinal abscess, joint effusion, platelet count (PLT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT), albumin (ALB), total bilirubin, lactate dehydrogenase (LDH), serum agglutination test (SAT), procalcitonin (PCT), and erythrocyte sedimentation rate (ESR) were associated with culture positivity. After multivariate adjustment, LDH, SAT, PCT, and ESR emerged as independent predictors of a positive blood culture, with PCT showing the strongest predictive value. Higher levels of LDH, SAT, PCT and ESR were independently associated with higher positive rates of blood cultures.

Conclusion: In this hospital-based retrospective cohort of confirmed brucellosis, LDH, SAT titer, PCT, and ESR were independently associated with blood-culture positivity. These routinely available parameters may help risk-stratify bacteremic likelihood and support culture-related decision-making (e.g., prioritizing sampling and considering repeat cultures when clinically warranted) among SAT-positive (or otherwise confirmed) patients, but they should not be interpreted as standalone markers for diagnosing Brucella bacteremia without microbiological confirmation.

Purpose: To assess the antioxidant-rich fraction of Murraya koenigii for its anti-infective properties against Gram-negative pathogenic bacteria by in vitro and in silico approaches.

Results: The most antioxidant active fraction, i.e., M. koenigii chloroform fraction (MKCF), significantly reduced violacein production (70.73%) in Chromobacterium violaceum 12,472. Significant reduction in prodigiosin production, protease activity, and swarming motility of Serratia marcescens, and other tested virulence factors of Pseudomonas aeruginosa PAO1 was recorded. More than 60% reduction in biofilm formation was recorded against test pathogens, indicating broad-spectrum anti-infective activity. SEM and CLSM imaging revealed alterations in the structure of the biofilm. Major key compounds such as Gibberellic acid, methyl ester, 7,8-Epoxylanostan-11-ol, 3-acetoxy were detected by GC/MS, and numerous compounds in MKCF were identified using LC-qTOF/MS analysis. In silico analysis revealed morellin and murrayazolinol with good binding affinity with CviR and EsaI, with binding energies of -9.07 and -9.17 kcal mol^-1, respectively.

Conclusion: The most active antioxidant fraction, i.e., MKCF, could be exploited as an anti-infective agent against Gram-negative bacterial pathogens, attenuating virulence and pathogenicity. Further, in vivo efficacy of the active fraction/phytocompounds needs to be evaluated to explore the therapeutic potential of MKCF.

Introduction: Carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a serious threat to public health. We characterized a rarely reported ST627-KL8 CRKP lineage associated with intensive care unit (ICU) transmission.

Methods: Three isolates (ZJG29565, ZJG30140, and ZJG30146) were obtained from three patients in the ICU and subjected to antimicrobial susceptibility testing. Whole-genome sequencing (WGS) was performed to determine genomic characteristics, phylogenetic relationships, and plasmid content, followed by assessments of mucoviscosity, capsule quantification, serum resistance, and bacterial virulence using a Galleria mellonella (G. mellonella) infection model. Additionally, bacterial capsule morphology was observed via transmission electron microscopy (TEM).

Results: SNP analysis (≤ 5 SNPs) confirmed clonal transmission within the ICU. Phylogenetic analysis placed ST627-KL8 as a distinct lineage closely related to ST14. All isolates carried an IncFII_K34 plasmid encoding bla _KPC-2, consistent with their carbapenem-resistant phenotype. Phenotypic assays-including TEM, mucoviscosity testing, serum resistance, and uronic acid quantification-demonstrated a thinner capsule and reduced mucoviscosity compared with the KL2 reference strain. In the Galleria mellonella model, ST627-KL8 exhibited intermediate virulence (66.7%-76.7% survival), between the hypervirulent K. pneumoniae ATCC 43816 strain (30.0%) and the low-virulence K. pneumoniae ATCC 700603 strain (96.7%).

Discussion: This study identified a novel ST627-KL8 CRKP clone with intermediate virulence, consistent with its reduced capsule phenotype and lack of classical hypervirulence genes. These features, together with the subtle clinical presentations, may contribute to reduced clinical vigilance and delayed optimization of antimicrobial therapy. Importantly, ST627-KL8 CRKP carried the IncFII_K34 bla _KPC-2 plasmid, which has been reported to exhibit high conjugation frequency, posing a significant challenge in clinical settings.

Bile acids (BAs), classically regarded as detergents for dietary lipid absorption, have emerged as pivotal signaling molecules with systemic endocrine functions. The discovery of the Farnesoid X Receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) as BAs-activated receptors unveiled their profound influences on glucose, lipid, and energy metabolism. BAs are first synthesized in hepatocytes and further metabolized by gut microbes, can either circulate in enterohepatic system or be found in circulations to exert various effects. More recently, the gut-brain axis has been identified as a critical pathway through which BAs exert significant effects on central nervous system (CNS) function and health. Based on research progresses mentioned above, this review systematically delineates the synthesis, metabolism, and classification of BAs, with a focus on the intricate crosstalk between the hepatic-gut BA axis and the brain. In addition, we explore the compelling evidences linking BAs dysregulation to a spectrum of neurological disorders, including neurodegenerative diseases (Alzheimer's and Parkinson's disease), depression, and hepatic encephalopathy. Besides, the potential mechanisms, such as alleviating neuroinflammation, maintaining the integrity of blood-brain barrier, increasing the neuronal survival, and modulating neurotransmitter systems are further elucidated. Finally, strategies of dietary intervention through phytochemicals to modulate the BAs pool for improved neurological outcomes are summarized and discussed. By integrating pre-clinical and clinical findings, this review aims to establish a foundation for understanding BAs as novel therapeutic targets in neurology and nutritional neuroscience.

Mercury (Hg) is a global environmental concern due to its microbial conversion to methylmercury (MeHg), a potent neurotoxin that bioaccumulates in food webs and poses risks to ecosystems and human health. Thiol functional groups (RSH) play an important role in controlling Hg(II) speciation and bio-uptake in methylating bacteria, yet the spatial distribution and density of these thiols within cells remain largely unknown. We isolated subcellular fractions of the Hg methylating bacterium Geobacter sulfurreducens in the exponential growth phase, and used Hg L _III -edge EXAFS (Extended X-ray Absorption Fine Structure) to quantify thiols in the extracellular medium, inner and outer membranes, periplasm and cytoplasm. The whole-cell thiol content was determined to be 1.3 × 10^-10 μmol cell^-1. The inner membrane contributed 7.1 × 10^-11 (53%), the outer membrane 1.2 × 10^-11 (9%), the periplasm 3.6 × 10^-11 (27%) and the cytoplasm 1.5 × 10^-11 μmol cell^-1 (11%). The extracellular fraction contributed an additional 5.7 × 10^-11 μmol cell^-1, corresponding to 30% of the thiols of the cell culture. Local thiol density (thiols normalized to TOC in individual compartment, RSH/TOC, μmol g^-1 C) was 36, 450, 140, 600 and 29 μmol g^-1 C in the cytoplasm, inner membrane, periplasm, outer membrane and extracellular fractions, respectively. EXAFS analyses demonstrate Hg-thiolate coordination across all compartments, with Hg-O/N bonding and elemental Hg⁰ formed at higher Hg loadings. In the periplasm, Hg-disulfide and traces of β-HgS were detected. The high thiol density at the membranes, relative to other compartments, may imply they have an important role in the retention and internalization of Hg(II). Periplasmic thiols may modulate Hg(II) transfer between membranes, and cytoplasmic thiols may regulate the intracellular availability of Hg(II) for methylation. This work provides the first compartment-resolved quantification of thiol abundances and densities in a model Hg-methylating bacterium at subcellular level, offering a mechanistic framework for understanding the speciation, bioavailability, and subcellular transformation of Hg(II) with relevance for other soft metals (e.g., Cd, Pb, Zn, Ag, and Cu).

Objective: Based on whole-genome sequencing (WGS) technology, the species distribution, genetic correlations, virulence and drug resistance gene characteristics of the clinical isolates of Mycobacterium abscessus complex (MABC) in the tropical island of China (Hainan) were analyzed to provide a basis for clinical precise diagnosis and treatment.

Methods: A total of 113 MABC strains from the Second Affiliated Hospital of Hainan Medical University from 2014 to 2023 were collected. Whole-genome sequencing (WGS) was used for subspecies identification (Average Nucleotide Identity, ANI), genetic distance analysis (single nucleotide polymorphism, SNP), and pan-genome analysis. The distribution of virulence and antibiotic resistance genes was analyzed through the Virulence Factor Database (VFDB) and the Comprehensive Antibiotic Resistance Database (CARD). The drug susceptibility phenotypes were detected by the microbroth dilution method.

Results: Among the 113 MABC strains, M. abscessus subsp. abscessus (Mab) accounted for 65.5%, M. abscessus subsp. massiliense (Mma) accounted for 33.6%, and M. abscessus subsp. bolletii (Mbo) accounted for 0.9%. The strains showed high genetic diversity among them, but two pairs of Mab strains with high genetic similarity (differing by 5 and 8 SNPs respectively) were identified, suggesting the possibility of local common exposure. The pan-genome is open-ended and consists of 3,626 core genes and highly variable accessory/unique genes. The virulence genes show species-specific differences: the detection rate of the phenolic lipid synthesis gene papA5 in Mma is significantly higher than that in Mab (92.1% vs. 47.3%, p < 0.001), while the PDIM synthesis gene ppsE is significantly lower in Mma (0.0% vs. 98.6%, p < 0.001). The drug sensitivity test shows that the 14-day induction of resistance rate of Mma to clarithromycin is significantly lower than that of Mab (5.3% vs. 86.5%, p < 0.001). Resistance genes are widely carried, including rrs a1408g (99.1%), rrl a2059g (98.2%) mutations, and the efflux pump gene qacJ in Mma (97.4%).

Conclusion: In Hainan region, environmental exposure is the main source of MABC infection. Whole genome analysis suggests the potential risk of local common exposure. Mma has a better treatment prospect due to its low clindamycin resistance rate. The differentiation of virulence and resistance genes among subtypes provides a molecular basis for the precise prevention and control of MABC infection in tropical regions.

Flavoenzymes of the 4-phenol oxidoreductase family are versatile biocatalysts that catalyze the oxidation of a wide variety of phenol derivatives to alcohols, aldehydes, ketones or alkenes. The promiscuous FAD-dependent vanillyl alcohol oxidases from Penicillium simplicissimum (PsVAO) and Diplodia corticola (DcVAO) have been described to catalyze the oxidative deamination of p-hydroxybenzylamines, giving rise to valuable flavor compounds, but starting from p-alkyl substituted phenols, the ketones are usually not accessible as these oxidases preferably stop at chiral benzylic alcohols. Here we took a closer look into the fungal VAO family with the aim to identify new members that can perform this deamination reaction and also the overoxidation of benzylic alcohols to ketones at a sufficient rate for application. Phylogenetic and amino acid cluster analysis revealed one clade that differed significantly in the constitution of the active site, while maintaining residues essential for catalysis. From this clade, five candidates were chosen for investigation, which revealed that VAO from Paecilomyces variotii (PvVAO) showed promising activities with vanillylamine and 4-(1-amino)ethylphenol, especially above pH 9.0, while also offering the ability to perform the overoxidation of p-alkyl substituted phenols toward ketones. Hence, the identified PvVAO offers two reaction routes toward benzylic ketones.

Growing interest in the circular economy has promoted the use of agri-food wastes as fermentable and readily available substrates for microbial cultivation, offering a sustainable and cost-effective strategy for natural pigment production. In this study, cheese whey was utilized as a nutritional substrate for pigment synthesis by an isolated strain identified as Agrococcus sp. NP24 (PQ097720.1). The work further aimed to characterize the produced pigment and evaluate its bioactivity. The culture medium was optimized using a Box-Behnken design (BBD). The carotenoid profile of the extracted pigment was analyzed by HPLC-DAD and LC-MS. Pigment stability was assessed across a range of pH values and temperatures, and its antimicrobial, antioxidant, and anticancer activities were examined. The pigment was identified as zeaxanthin monoester (C14:0). The maximum pigment yield (0.0567 mg/mL extract) was achieved after 72 h at 20 °C using a medium containing 80% whey (v/v), 0.5% peptone (w/v), 0.97 g % casein (w/v), and supplemented with 0.5% (w/v) yeast extract and 0.5% (w/v) MgSO₄. The pigment remained fully stable up to 50 °C. Acidic conditions (pH 3-5) enhanced pigment absorbance compared to neutral and alkaline pHs. In contrast, exposure to daylight markedly reduced pigment stability, leaving only 26% residual activity after 1 h. The pigment exhibited potent antioxidant activity with an IC₅₀ of 6 μg/mL. It also showed cytotoxic and significant selectivity against the triple-negative breast cancer cell line MDA-MB-231 and the colorectal carcinoma cell line HCT-116, with IC₅₀ values of 3.3 mg/mL and 0.56 mg/mL, respectively, while no cytotoxicity was observed toward the HepG-2 hepatoblastoma cell line. The carotenoid did not display significant antimicrobial activity. In conclusion, the cost-effective production of NP24 carotenoids, combined with their favorable stability and bioactivity, supports their potential use as natural colorants in food applications.