Search Results (6)

Dietary interventions using probiotics actively regulate metabolism in obesity and type 2 diabetes. This study aimed to characterize two novel co-isolated strains, P. pentosaceus BGI-N8 and P. acidilactici BGI-N9, using an integrated genome–phenotype approach. Whole-genome sequencing established their preliminary safety and functional genotypes, followed by in vitro assays measuring gastrointestinal tolerance, adhesion, and metabolic enzyme activity. Genomic analysis revealed that both strains achieved genome-based safety levels, and no high-confidence transferable AMR determinants and canonical virulence factors were identified. Functional annotation showed that BGI-N8 and BGI-N9 contain essential genes for gastrointestinal adaptation, including F0F1-ATPase, the dltA-D operon, and the opp transport system. Phenotypically, BGI-N9 exhibited superior acid resistance (79.3% survival at pH 2.0), while both strains showed robust auto-aggregation (>70%) and high adhesion to HT-29 cells (ranged from 5.4 to 5.9 adherent bacteria per cell). Furthermore, the strains displayed inhibitory activity against selected indicator pathogens (88.6–97.6% inhibition). Notably, BGI-N8 and BGI-N9 showed comparable α-glucosidase inhibitory activities, with inhibition rates of 44.53% and 39.94%, respectively, Both strains also exhibited comparable cholesterol-removal capacities under the tested conditions, with removal rates of 68.76% and 74.49%. Overall, these genomic and phenotypic results supported the potentials of BGI-N8 and BGI-N9 as candidate probiotic strains with distinct complementary strengths in glycolipid regulation, providing a theoretical basis for their synergistic application. Further mechanistic, safety, and in vivo studies are required to validate their metabolic-health-related relevance. Full article

The emergence of vancomycin-intermediate Staphylococcus aureus (VISA) threatens the efficacy of this last-line antibiotic. The GraSR two-component system is frequently mutated in VISA strains. Here, we demonstrate that the GraS(T136I) point mutation, identified in the clinical VISA isolate XN108, is a key determinant of reduced vancomycin susceptibility. Introducing this mutation into the susceptible strain Newman increased the vancomycin MIC from 1.5 to 4 mg/L, while its reversion in XN108 decreased the MIC from 12 to 8 mg/L. The mutation conferred common phenotypes, including thickened cell wall, decreased autolysis, and reduced cell surface negative charge via upregulation of the dltABCD operon and mprF. Notably, the GraS(T136I) mutation also upregulated virulence genes (efb, hlb, sbi, hld) and enhanced hemolytic activity. Interestingly, despite this hypervirulent profile, the mutant showed impaired long-term survival within macrophages. Our study reveals that a single GraSR mutation can co-regulate vancomycin resistance and virulence, offering new insights into the adaptation of S. aureus to antibiotic pressure. Full article

Staphylococcus aureus (S. aureus) is a major Gram-positive pathogen, and treatment of S. aureus infections is often challenging due to widespread antibiotic resistance. In Gram-positive bacteria such as S. aureus, D-alanylation of teichoic acids (TA) reduces the net negative charge of the cell envelope and contributes to resistance to diverse antibiotics, particularly cationic antimicrobial peptides. D-alanylation is mediated by the dltABCD operon, which encodes four proteins (DltA, DltB, DltC, and DltD), all of which is essential for the multistep transfer of D-alanine to teichoic acids. Here, we present the first crystal structure of the S. aureus D-alanyl carrier protein DltC and analyze its interaction with DltA using AlphaFold3 and all-atom molecular dynamics simulations. We further show that single substitutions of SaDltA-SaDltC interface residues abolish SaDltC mediated enhancement of SaDltA catalysis. Together, these findings define a catalytically critical S. aureus DltA-DltC interface and provide a structural insight for targeting the D-alanylation pathway as a potential anti-Staphylococcus strategy. Full article

Methicillin-resistant Staphylococcus aureus (MRSA) infection is a serious clinical threat, and D-Serine (D-Ser) showed significant sensitization effects on β-lactams against MRSA in our previous study. Quantitative PCR analysis found the elevated expression of the dlt operon with D-Ser combination, which is responsible for wall teichoic acid (WTA) modification involving D-Alanine (D-Ala). This study aims to verify the effect of D-Ser on WTA modification through the dlt pathway and explore the related effects on bacteria. The DltA and DltC were recombined, and enzyme kinetic evaluations with different D-amino acids were then conducted; it was found that D-Ser is the second-best substrate for DltA (just after D-Ala), no matter whether DltC is present or not. D-Ser treatment also lowered WTA generation as demonstrated by WTA phosphate quantification and native-PAGE electrophoresis, increased the susceptibility of S. aureus to polymyxins, and elevated the mouse survival rate in the MRSA intraperitoneal infection model without affecting the bacterial loads in the main organs, indicating possible effects of D-Ser on MRSA virulence through WTA modification. In conclusion, the current study provided evidence for D-Ser modification of WTA via the dlt pathway, and its possible involvement in D-Ser sensitization deserves further investigation. Full article

Hop beta acids (HBAs) are characteristic compounds from the hop plant that are of interest for their strong antimicrobial activity. In this work, we report a resistance mechanism against HBA in the foodborne pathogen Listeria monocytogenes. Using an evolution experiment, we isolated two HBA-resistant mutants with mutations in the mprF gene, which codes for the Multiple Peptide Resistance Factor, an enzyme that confers resistance to cationic peptides and antibiotics in several Gram-positive bacteria by lysinylating membrane phospholipids. Besides the deletion of mprF, the deletion of dltA, which mediates the alanylation of teichoic acids, resulted in increased HBA resistance, suggesting that resistance may be caused by a reduction in positive charges on the cell surface. Additionally, we found that this resistance is maintained at low pH, indicating that the resistance mechanism is not solely based on electrostatic interactions of HBA with the cell surface. Finally, we showed that the HBA-resistant mutants display collateral sensitivity to the cationic antimicrobials polymyxin B and nisin, which may open perspectives for combining antimicrobials to prevent resistance development. Full article

Lactobacillus gasseri and Lactobacillus paragasseri are human commensal lactobacilli that are candidates for probiotic application. Knowledge of their oligosaccharide metabolic properties is valuable for synbiotic application. The present study characterized oligosaccharide metabolic systems and their impact on lipoteichoic acid (LTA) production in the two organisms, i.e., L. gasseri JCM 1131^T and L. paragasseri JCM 11657. The two strains grew well in medium with glucose but poorly in medium with raffinose, and growth rates in medium with kestose differed between the strains. Oligosaccharide metabolism markedly influenced their LTA production, and apparent molecular size of LTA in electrophoresis recovered from cells cultured with glucose and kestose differed from that from cells cultured with raffinose in the strains. On the other hand, more than 15-fold more LTA was observed in the L. gasseri cells cultured with raffinose when compared with glucose or kestose after incubation for 15 h. Transcriptome analysis identified glycoside hydrolase family 32 enzyme as a potential kestose hydrolysis enzyme in the two strains. Transcriptomic levels of multiple genes in the dlt operon, involved in D-alanine substitution of LTA, were lower in cells cultured with raffinose than in those cultured with kestose or glucose. This suggested that the different sizes of LTA observed among the carbohydrates tested were partly due to different levels of alanylation of LTA. The present study indicates that available oligosaccharide has the impact on the LTA production of the industrially important lactobacilli, which might influence their probiotic properties. Full article