Search Results (261)

Streptococcus iniae (S. iniae) is a globally significant aquatic pathogen responsible for severe economic losses in aquaculture. While the S. iniae infection often exhibits distinct seasonal patterns strongly correlated with water temperature, there is limited knowledge regarding the temperature-dependent immune evasion strategies of S. iniae. Our results demonstrated a striking temperature-dependent virulence phenotype, with significantly higher A. latus mortality rates observed at high temperature (HT, 33 °C) compared to low temperature (LT, 23 °C). Proteomic analysis revealed temperature-dependent upregulation of key virulence factors, including streptolysin S-related proteins (SagG, SagH), antioxidant-related proteins (SodA), and multiple capsular polysaccharide (cps) synthesis proteins (cpsD, cpsH, cpsL, cpsY). Flow cytometry analysis showed that HT infection significantly reduced the percentage of lymphocyte and myeloid cell populations in the head kidney leukocytes of A. latus, which was associated with elevated caspase-3/7 expression and increased apoptosis. In addition, HT infection significantly inhibited the release of reactive oxygen species (ROS) but not nitric oxide (NO) production. Using S. iniae cps-deficient mutant, Δcps, we demonstrated that the cps is essential for temperature-dependent phagocytosis resistance in S. iniae, as phagocytic activity against Δcps remained unchanged across temperatures, while NS-1 showed significantly reduced uptake at HT. These findings provide new insights into the immune evasion of S. iniae under thermal regulation, deepening our understanding of the thermal adaptation of aquatic bacterial pathogens. Full article

Background: Antibiotics at sub-inhibitory concentrations can rewire bacterial regulatory networks, impacting virulence. Objective: The way that exposure to selected antibiotics (ciprofloxacin, amikacin, azithromycin, ceftazidime, and meropenem) below their minimum inhibitory concentration (sub-MIC) modulates the physiology of Pseudomonas aeruginosa is examined in this study using growth-phase-resolved analysis. Methods: Standard P. aeruginosa strain cultures were exposed to ¼ and ½ MIC to determine the growth kinetics under antibiotic stress. The study measured protease and pyocyanin production and the expression level of important quorum sensing and virulence genes (lasI/R, rhlI/R, pqsR/A, and phzA) at different growth phases. Results: Meropenem produced the most noticeable growth suppression at ½ MIC. Sub-MIC antibiotics did not completely stop growth, but caused distinct, dose-dependent changes. Azithromycin eliminated protease activity in all phases and had a biphasic effect on pyocyanin. Ciprofloxacin consistently inhibited both pyocyanin and protease in all phases. The effects of amikacin varied by phase and dose, while β-lactams markedly increased pyocyanin production during the log phase. In contrast to the plateau phase, when expression was often downregulated or unchanged, most quorum-sensing- and virulence-associated genes showed significant upregulation during the death phase under sub-MIC exposure. Conclusions: These findings indicate that sub-MIC antibiotics act as biochemical signal modulators, preserving stress-adapted sub-populations that, in late growth phases, activate quorum sensing and stress tolerance pathways. Full article

Pseudomonas aeruginosa biofilm formation is critical to antibiotic resistance and persistence. Targeting cyclic di-GMP (c-di-GMP) signaling, a master biofilm formation and virulence regulator, presents a promising strategy to combat resistant bacterial infections. Myricetin, a natural polyphenolic flavonoid with documented antimicrobial and anti-biofilm activities, may enhance antibiotic efficacy against Pseudomonas aeruginosa. This study evaluated the synergistic effects of myricetin combined with azithromycin, ciprofloxacin, or cefdinir against both standard and drug-resistant Pseudomonas aeruginosa strains. Antibacterial activity, biofilm disruption, and motility inhibition were experimentally assessed, while molecular dynamic (MD) simulations elucidated myricetin’s molecular mechanism of action. Our results suggested that myricetin synergistically potentiated all three antibiotics, reducing c-di-GMP synthesis by 28% (azithromycin), 57% (ciprofloxacin), and 30% (cefdinir). It enhanced bactericidal effects, suppressed biofilm formation, and impaired swimming, swarming, and twitching motility. Computational analyses revealed that myricetin binds allosterically to FimX very well, a key regulator in the c-di-GMP signaling pathway. Hence, myricetin may act as a c-di-GMP inhibitor, reversing biofilm-mediated resistance in Pseudomonas aeruginosa and augmenting antibiotic efficacy. This integrated experimental and computational approach provides a framework for developing anti-virulence and antibiotic combination therapies against recalcitrant Gram-negative pathogens. Full article

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp), a pathogen causing severe nosocomial infections and high mortality rates, is increasingly becoming a serious global public health threat. Capsular polysaccharide (CPS), a major virulence factor of hvKp, can be enzymatically degraded by bacteriophage-derived depolymerases. However, to our knowledge, depolymerases targeting K. pneumoniae K54-type strains have rarely been identified. Here, we identified and characterized three novel capsule depolymerases, Dep_C, Dep_Y, and Dep_Z, derived from three different K. pneumoniae phages, which retained robust activity across a broad pH range (pH 3.0–12.0) and demonstrated thermal stability up to 50 °C. These depolymerases could efficiently digest the CPS of K. pneumoniae K54-serotype strains, significantly inhibit biofilm formation, and remove their mature biofilms. Although no bactericidal activity was detected, these depolymerases rendered host bacteria susceptible to serum complement-mediated killing. We further demonstrate that Dep_C, Dep_Y, and Dep_Z can effectively and significantly prolong the survival time of mice in a pneumonia model infected with K54-type K. pneumoniae and reduce the colonization and virulence of the bacteria in the mice. These findings indicate that depolymerases Dep_C, Dep_Y, and Dep_Z could increase bacterial susceptibility to host immune responses of hvKp to the host through their degradation effect on the CPS. In conclusion, our study demonstrates that the three capsule depolymerases are promising antivirulent agents to combat CR-hvKp infections. Full article

The growing threat of antibiotic-resistant Gram-negative bacteria highlights the urgent need for innovative, non-bactericidal therapeutic strategies. Quorum-sensing (QS) inhibition has emerged as a promising approach to attenuate bacterial virulence without exerting selective pressure. This study evaluated the antimicrobial, anti-QS, and antibiofilm properties of aqueous extracts from five medicinal plants native to northeastern Mexico: Gymnosperma glutinosum, Ibervillea sonorae, Larrea tridentata, Olea europaea, and Tecoma stans. Disk diffusion and violacein quantification assays using Chromobacterium violaceum demonstrated significant QS inhibition by G. glutinosum and T. stans, with violacein reductions of 60.02% and 52.72%, respectively, at 40 mg/mL. While L. tridentata and O. europaea exhibited antibacterial activity, I. sonorae showed no growth or pigment inhibition but achieved the highest biofilm disruption (89.89%) against Salmonella typhimurium. UPLC-MS analysis identified chlorogenic acid, kaempferol, and D-(−)-quinic acid as major constituents, compounds previously associated with QS modulation. These findings highlight the potential of traditional Mexican plant species as sources of QS inhibitors and bio-film-disrupting agents, supporting their further development as alternatives to conventional antibiotics. Full article

Streptococcus pneumoniae (S. pneumoniae) Sortase A (SrtA) anchors virulence proteins to the surface of the cell wall by recognizing and cleaving the LPXTG motif. These toxins help bacteria adhere to and colonize host cells, promote biofilm formation, and trigger host inflammatory responses. Therefore, SrtA is an ideal target for the development of new preparations for S. pneumoniae. In this study, we found that phloretin (pht) and phlorizin (phz) exhibited excellent affinities for SrtA based on virtual screening experiments. We analyzed the interactive mechanism between pht, phz, and alnusone (aln, a reported S. pneumoniae SrtA inhibitor) and SrtA based on molecular dynamics simulation experiments. The results showed that these inhibitors bound to the active pocket of SrtA, and the root mean square deviation (RMSD) and distance analyses showed that these compounds and SrtA maintained stable configuration and binding during the assay. The binding free energy analysis showed that both electrostatic forces (ele), van der Waals forces (vdw), and hydrogen bonds (Hbonds) promoted the binding between pht, phz, and SrtA; however, for the binding of aln and SrtA, the vdw force was much stronger than ele, and Hbonds were not found. The binding free energy decomposition showed that HIS141, ILE143, and PHE119 contributed more energy to promote pht and SrtA binding; ARG215, ASP188, and LEU210 contributed more energy to promote phz and SrtA binding; and HIS141, ASP209, and ARG215 contributed more energy to promote aln and SrtA binding. Finally, the transpeptidase activity of SrtA decreased significantly when treated with different concentrations of pht, phz, or aln, which inhibited S. pneumoniae biofilm formation and adhesion to A549 cells without affecting normal bacterial growth. These results suggest that pht, phtz, and aln are potential materials for the development of novel inhibitors against S. pneumoniae infection. Full article

In recent years, one of the most important issues in public health is the rapid growth of antibiotic resistance among pathogens. Multidrug-resistant (MDR) strains (mainly Enterobacteriaceae and non-fermenting bacilli) cause severe infections, against which commonly used pharmaceuticals are ineffective. Therefore, there is an urgent need for new treatment options and drugs with innovative mechanisms of action. Natural compounds, especially alkaloids, are showing promising potential in this area. This review focuses on the ability of the isoquinoline alkaloid berberine (BRB) to overcome various resistance mechanisms against conventional antimicrobial agents. BRB has demonstrated significant activity in inhibiting efflux pumps of the RND (Resistance-Nodulation-Cell Division) family, such as MexAB-OprM (P. aeruginosa) and AdeABC (A. baumannii). Moreover, BRB was able to decrease quorum sensing activity in both Gram-positive and Gram-negative pathogens, resulting in reduced biofilm formation and lower bacterial virulence. Additionally, BRB has been identified as a potential inhibitor of FtsZ, a key protein responsible for bacterial cell division. Particularly noteworthy, though requiring further investigation, are reports suggesting that BRB might inhibit β-lactamase enzymes, including NDM, AmpC, and ESβL types. The pleiotropic antibacterial actions of BRB, distinct from the mechanisms of traditional antibiotics, offer hope for breaking bacterial resistance. However, more extensive studies, especially in vivo, are necessary to fully evaluate the clinical potential of BRB and determine its practical applicability in combating antibiotic-resistant infections. Full article

The quorum-quenching activity of essential oils (EOs) from Corsican aromatic plants was evaluated using the marine bacterium Aliivibrio fischeri as a model system. Among the eleven EOs screened, Myrtus communis EO showed significant interference with QS-regulated phenotypes (swimming motility, bioluminescence, and biofilm formation). Its activity was compared to Origanum vulgaris EO, known for its high carvacrol content and potent QS inhibition. The fractionation of M. communis EO revealed that its most polar fractions exhibited comparable levels of QS-disrupting activity. These chromatographic fractions significantly affected QS-controlled traits, indicating that minor or less volatile compounds may contribute to, or enhance, the overall bioactivity. Furthermore, M. communis EO and its polar fractions displayed stronger anti-QS effects against A. fischeri than O. vulgaris EO. These results highlight M. communis EO as a promising source of natural QS inhibitors and underscore the importance of exploring both complete EOs and their active fractions. This study supports the valorization of Mediterranean endemic flora as a reservoir of bioactive compounds, tested on a model system A. fischeri, and encourages future research on the potential of Myrtus communis against clinical bacterial isolates and the development of novel anti-virulence strategies. Full article

The development of antimicrobial resistance drives the search for molecules capable of inhibiting bacterial virulence. Fungi of the Basidiomycota phylum constitute an important source of compounds with antimicrobial activity. The present paper describes a new species named Fulvifomes mexicanus sp. nov. based on morphological and phylogenetic analyses. The methanolic extract of basidiome of this fungus inhibited the motility of Pseudomonas aeruginosa ATCC 9027 and the production of violacein by Chromobacterium violaceum CV026. The metabolomic study of the extract by liquid chromatography–high-resolution electrospray ionization mass spectrometry (LC-HRESIMS) and molecular networking analyses revealed the presence of a complex composition of metabolites including hispidin derivatives, terpenoids, phenols, furanones, alkylglycerols, pyrones, and γ-butyrolactones, among others. Overall, this work represents the first chemical and biological study of a new species of Fulvifomes mexicanus as a source of antipathogenic metabolites for the development of novel antimicrobial agents. Full article

Staphylococcus aureus and coagulase-negative staphylococci (CNS) are the main causative agents of mastitis in sheep. Their ability to form biofilms in vivo is considered an important virulence factor underlying mastitis outbreaks refractory to antibiotic treatments. Furthermore, pre- and postdipping immersion during milking in iodine substances could determine the presence of residues in milk and therefore represent a health risk factor for consumers. The aim of this study was to evaluate the antibacterial and biofilm inhibitory activity of Thymus vulgaris L. essential oil (TEO) against staphylococci strains isolated from ovine clinical mastitis. In particular, 3 reference strains (S. aureus 25923 and 11623 and S. epidermidis 12228) and 12 clinical isolates (6 S. aureus and 6 CNS) were used. TEO solutions, from a concentration of 1% (v/v) to 1.25% (v/v), corresponding to 9.28–2.32 mg/mL, were obtained after solubilization in 10% dimethyl sulfoxide (DMSO) and used to evaluate the bacterial time-kill compared to that of an iodine-based solution. Antibacterial efficacy was then assessed by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), while biofilm inhibition was assessed by minimum biofilm inhibitory concentration (MBIC) using a spectrophotometer at a wavelength of 570 nm. Additionally, biofilm-associated genes (icaA and icaD) were evaluated in all tested strains by PCR. The tested TEO concentrations were able to significantly and prominently reduce bacterial growth compared to controls, as demonstrated by bacterial time-kills. The MIC value was obtained at a concentration of 0.50% (v/v) for a single coagulation-positive isolate (S. aureus (f)) and at a concentration of 0.25% (v/v) for all other isolates. TEO showed effective bactericidal action with a 99.9% reduction in CFU/mL of all isolates in the MBC test at a concentration of 0.25% (v/v) for most of the tested strains. Furthermore, a marked inhibition in biofilm formation at all tested concentrations was observed, with MBIC value of 0.25%. All S. aureus tested were biofilm-producing strains and positive for icaA and icaD genes, while two CNS biofilm-producing strains were negative for both genes. These preliminary results suggest that TEO could be a promising alternative as an udder disinfectant during milking practices. Although in vivo studies are needed to confirm the efficacy and safety of TEO as an adjuvant in the prevention and treatment of udder infections, TEO could help counteract the emergence of antimicrobial resistance and reduce the potential risk of iodine residues in milk. Full article

Background: Disruption of the natural balance of the skin microbiota can impair wound healing and contribute to chronic infections. Identifying the bacterial species involved and understanding their antimicrobial susceptibility profiles are essential for guiding treatment, especially given the growing threat of antibiotic resistance. Methods: This study characterized the virulence and antibiotic resistance phenotypes of 43 bacterial strains isolated from chronic wounds. The antimicrobial activity of selected essential oils (sandalwood, ylang-ylang, sage, cajeput, and juniper), pharmaceutical products (propolis tinctures, usnic acid), and probiotic lactic acid bacteria strains (Lactobacillus spp., Lactococcus lactis) was assessed using qualitative and quantitative assays, including MIC, MICBA, and co-culture evaluations. Results: Gram-positive strains were more sensitive to essential oils than Gram-negative strains, with sandalwood, ylang-ylang, and propolis tincture showing the strongest antibacterial effects. These agents also showed significant biofilm inhibition. Probiotic strains exhibited antimicrobial activity against Staphylococcus aureus and Morganella morganii, with Lactobacillus paracasei and Lactobacillus rhamnosus being particularly effective in reducing bacterial growth and adhesion in vitro. Conclusions: Essential oils and probiotic strains demonstrate promising antimicrobial effects against chronic wound pathogens and may serve as alternative or adjunctive treatments to antibiotics. Further clinical research and standardization are necessary to establish their safety, efficacy, and optimal application protocols. Full article

Background/Objectives: Wine pomace is a rich source of bioactive phenolic compounds with potential health benefits. This study aimed to evaluate the antipathogenic and antioxidant properties of ethanol and ethyl acetate extracts from wine pomace of three grape varietals (Tannat, Bonarda, and Malbec) to explore their potential as natural alternatives for mitigating bacterial virulence in Pseudomonas aeruginosa. Methods: Successive exhaustion extractions were performed using solvents of increasing polarity (ethyl acetate and ethanol). The phenolic content was quantified, and the antioxidant activity was evaluated using standard assays. The antipathogenic activity against P. aeruginosa was assessed by measuring biofilm formation, elastase and protease activity, pyocyanin production, and swarming motility. Quorum sensing (QS) inhibition was tested using a violacein production assay in Chromobacterium violaceum. Results: Ethanol was more effective at extracting phenolic compounds, with Tannat exhibiting the highest total phenolic content (162.5 µg GAE/mg). HPLC-DAD analysis identified 16 phenolic acids, 18 flavonoids, and 3 stilbenes across the extracts. The ethanol extracts showed strong antioxidant activity (phosphomolybdenum reducing capacity 67–128 μg AAE/mg, ABTS^•+ scavenging 37–71 µg/mL, Fe³⁺ reducing power 31–68 µg/mL) and inhibited biofilm formation (up to 61%), elastase (up to 41%), and protease (up to 46%) activities in P. aeruginosa. The extracts also reduced pyocyanin production (up to 78%) and swarming motility (up to 68%), suggesting interference with QS. Moreover, the extracts inhibited violacein production in C. violaceum, confirming QS inhibition (up to 26%). Conclusions: Among the extracts, ethanol-extracted Tannat pomace showed the most substantial antipathogenic and antioxidant activities. The results add value to wine pomace by suggesting its use as natural extracts rich in phenolic compounds, capable of controlling the bacterial virulence of Pseudomonas aeruginosa without promoting the development of resistance. Full article

Lysyl-phosphatidylglycerol (lysyl-PG) is one of the major lipids found in bacterial membranes; it is synthesized by attaching lysine to the headgroup of phosphatidylglycerol. First identified in Staphylococcus aureus in 1964, lysyl-PG is now recognized as a virulence factor that protects Staphylococcus aureus from antimicrobial agents, such as cationic antimicrobial peptides and phospholipase A2 type IIA. Under normal growth conditions, Staphylococcus aureus membranes are negatively charged due to a high proportion of anionic lipids, such as phosphatidylglycerol and cardiolipin. This intrinsic anionic charge helps attract positively charged antimicrobial agents to the membrane surface, increasing their disruptive activity. The presence of lysyl-PG reduces electrostatic interactions, making the membrane less susceptible to cationic agents. The biosynthesis of lysyl-PG is mediated by the multiple peptide resistance factor (MprF) enzyme, which catalyzes the modification of phosphatidylglycerol and translocation of lysyl-PG to the outer membrane in the presence of antimicrobial agents. However, several studies indicate that lysyl-PG not only responds to the presence of antimicrobial agents but can fluctuate based on environmental factors such as oxygen availability and nutrient composition. Acidic conditions and nutrient-rich media often result in increased lysyl-PG production, suggesting that bacterial membranes can be resistant to cationic antimicrobial agents even in their native state. Recent studies propose that targeting MprF to inhibit lysyl-PG biosynthesis could be a promising strategy to counter antimicrobial resistance. This review highlights the role of lysyl-PG in modulating membrane charge and its influence on antimicrobial agent efficacy and discusses a possible strategy for treatment by targeting lysyl-PG synthesis. Full article

Fucoidan is a sulfated fucan marine polysaccharide with potential therapeutic applications, including antibacterial activity and the control of virulence factors associated with quorum sensing. This study investigates the bioactivity of fucoidan derived from the brown algae Ascophyllum nodosum, as well as their fucoidan oligosaccharides (OFuc; <3 kDa), on the growth, motility, biofilm formation, and adhesion of Campylobacter jejuni, the leading cause of bacterial gastroenteritis worldwide. The results showed that fucoidan decreased the growth rate of C. jejuni at concentrations greater than 25 µg/mL, while no effect was observed with different concentrations (5–100 µg/mL) of OFuc. Neither compound affected bacterial motility. Both fucoidan and OFuc inhibited abiotic biofilm formation and diminished pathogen adhesion in a concentration-dependent manner. The study also found that C. jejuni recognized the fucoidan molecule through an enzyme-like lectin assay (ELLA) showing a lectin-like adhesin-carbohydrate recognition. Overall, these results suggest the potential of fucoidan from A. nodosum for controlling abiotic biofilm formation in the food industry, and they open new avenues for research into the use of fucoidan as a molecule aimed at blocking infections caused by C. jejuni. Full article

The use of antibiotics has greatly improved the treatment of bacterial infections; however, its abuse and misuse has led to a rapid rise in multidrug-resistant (MDR) bacteria. Therefore, the search for new antimicrobial strategies has become critical. Natural flavonoids, a class of widely existing phytochemicals, have gained significant research interest for their diverse biological activities and antibacterial effects on various drug-resistant bacteria. This review summarizes the latest research progress on flavonoids, with a particular focus on several flavonoids exhibiting certain antibacterial activity, and explores their antibacterial mechanisms, including disruption of cell membranes and cell walls, inhibition of proteins and nucleic acids, interference with signal transduction, suppression of efflux pump activity, and inhibition of biofilm formation and virulence factor production. Additionally, we have reviewed the synergistic combinations of flavonoids with antibiotics, such as the combination of quercetin with colistin or EGCG with tetracycline, which significantly enhance therapeutic efficacy. Full article