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Keywords = sub-inhibitory MIC

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29 pages, 3396 KB  
Article
Exploitation of Nanoparticle–Essential Oil Combinations to Enhance the Efficacy of Antimicrobial Agents Against Staphylococcus equorum
by Simona Hisirová, Patrícia Hudecová, Vanda Hajdučková, Stanislav Lauko, Nikola Dančová, Lívia Mačák, Oksana Velgosova, Peter Paľove-Balang and Ján Király
Pharmaceutics 2026, 18(8), 1017; https://doi.org/10.3390/pharmaceutics18081017 - 17 Aug 2026
Viewed by 227
Abstract
Background: This study evaluated the antibacterial, antibiofilm, and biofilm eradication activities of biogenically synthesized silver nanoparticles (AgNPs-L, AgNPs-R) mediated by extracts of Lavandula angustifolia and Salvia rosmarinus, individually and in combination with their respective essential oils (EOs) and ampicillin (AMP), against a [...] Read more.
Background: This study evaluated the antibacterial, antibiofilm, and biofilm eradication activities of biogenically synthesized silver nanoparticles (AgNPs-L, AgNPs-R) mediated by extracts of Lavandula angustifolia and Salvia rosmarinus, individually and in combination with their respective essential oils (EOs) and ampicillin (AMP), against a multidrug-resistant biofilm-forming Staphylococcus equorum strain. Physicochemical characterization confirmed the successful biosynthesis of spherical AgNPs-L (10–25 nm) and AgNPs-R (5–15 nm). Individual treatments exhibited distinct antibacterial activity, with MIC values of 25 µg/mL for AgNPs-L, 12.5 µg/mL for AgNPs-R, and 0.1% (v/v) for both EOs; however, they showed no ability to eradicate preformed biofilms. Dual AgNPs/EO combinations at subinhibitory concentrations demonstrated borderline additive effects (FICI = 0.501) and significantly potentiated antibacterial and antibiofilm activity compared with individual treatments. Triple AgNPs/EO/AMP combinations exhibited the most pronounced biological effects, with predominantly additive interactions depending on AMP concentration. Lavender-based triple combinations achieved up to 63.9% inhibition of planktonic growth, 78.1% prevention of biofilm formation, and 37.3% eradication of mature biofilms, whereas rosemary-based combinations resulted in 57.1%, 69.4%, and 42.7% inhibition, respectively. These findings highlight the potential of multi-component systems integrating biogenic nanomaterials, phytochemicals, and conventional antibiotics as a promising strategy to enhance antimicrobial efficacy against persistent biofilm-forming non-aureus staphylococci. Full article
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21 pages, 22115 KB  
Article
Comparative Phenotypic and Transcriptomic Analysis Reveals Distinct Yet Partially Convergent Mechanisms of Daphnetin and 6-Methylcoumarin Against Eucalyptus-Derived Ralstonia pseudosolanacearum
by Han Xue, Ning Jiang and Yong Li
Microorganisms 2026, 14(8), 1799; https://doi.org/10.3390/microorganisms14081799 - 14 Aug 2026
Viewed by 236
Abstract
Eucalyptus bacterial wilt in China, caused predominantly by Ralstonia pseudosolanacearum, severely threatens Eucalyptus plantation management in China and demands plant-derived alternatives to conventional bactericides. This study evaluated the in vitro antibacterial activities and underlying molecular mechanisms of two differentially substituted coumarin derivatives, [...] Read more.
Eucalyptus bacterial wilt in China, caused predominantly by Ralstonia pseudosolanacearum, severely threatens Eucalyptus plantation management in China and demands plant-derived alternatives to conventional bactericides. This study evaluated the in vitro antibacterial activities and underlying molecular mechanisms of two differentially substituted coumarin derivatives, daphnetin (DAP) and 6-methylcoumarin (MC), against a eucalyptus-derived R. pseudosolanacearum strain. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using broth microdilution assays. Quantitative phenotypic assays were conducted to evaluate the effects of sub-lethal concentrations on biofilm formation, swimming motility, and extracellular polysaccharide (EPS) accumulation. Furthermore, high-throughput RNA sequencing integrated with GO and KEGG enrichment analyses was employed to characterize the genome-wide transcriptomic responses. Antimicrobial susceptibility testing demonstrated that DAP possessed superior bactericidal efficacy, yielding lower MIC (62.5 μg/mL) and MBC (250 μg/mL) values than MC. Conversely, sub-lethal MC exhibited a more pronounced, early-stage suppression of flagellum-dependent swimming motility and biofilm maturation. Both compounds consistently attenuated EPS production. Transcriptomic analysis revealed distinct yet partially convergent regulatory networks: DAP primarily exerted metabolic strangulation by downregulating genes governing aerobic respiratory chains and peripheral carbon/nitrogen pathways, whereas MC targeted collective behavior and active pathogenesis, systematically downregulating the expression of genes associated with flagellar assembly, quorum sensing, and Type III and VI secretion systems. Notably, both pathways converged downstream to repress the master virulence regulator xpsR and the epsA-P operon. These findings provide valuable insights into the potential molecular pathways affected by DAP and MC, offering a useful reference for future exploration of botanical formulations for ecologically responsible forest disease control. Full article
(This article belongs to the Section Molecular Microbiology and Immunology)
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20 pages, 2422 KB  
Article
Anti-Biofilm Activity of (+)-Endo-Borneol Against Streptococcus mutans: Experimental Evaluation, Virulence Gene Expression Analysis, and Molecular Docking
by Gayane Atazhanova, Karakoz Badekova, Yana Levaya, Assel Sabiyeva, Tomas Kacergius, Vika Gabe, Irina Kadyrova, Altyn Bakenova, Almagul Makhmutova, Daniyar Sadyrbekov, Assanali Ainabayev and Elina Smagulova
Plants 2026, 15(16), 2417; https://doi.org/10.3390/plants15162417 - 7 Aug 2026
Viewed by 242
Abstract
Streptococcus mutans is the primary etiological agent of dental caries due to its ability to form acidogenic biofilms on tooth surfaces. Natural monoterpenes have attracted considerable interest as potential antibiofilm agents for oral healthcare. The present study investigated the antibiofilm activity and possible [...] Read more.
Streptococcus mutans is the primary etiological agent of dental caries due to its ability to form acidogenic biofilms on tooth surfaces. Natural monoterpenes have attracted considerable interest as potential antibiofilm agents for oral healthcare. The present study investigated the antibiofilm activity and possible mechanism of action of (+)-endo-borneol isolated from the essential oil of Achillea millefolium against S. mutans. The chemical composition of the essential oil was characterized by gas chromatography–mass spectrometry (GC–MS), and (+)-endo-borneol was isolated by chromatographic separation. Antibiofilm activity was evaluated using the crystal violet biofilm assay, while antimicrobial activity was determined by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. The influence of subinhibitory concentrations of (+)-endo-borneol on the expression of the biofilm-associated genes gtfB and yycF was assessed by quantitative real-time PCR. Molecular docking was performed to investigate ligand–protein interactions, using a ligand geometry pre-optimized by density functional theory (DFT, B3LYP/6-31G**). The essential oil inhibited S. mutans biofilm formation by up to 98%, whereas isolated (+)-endo-borneol reduced biofilm biomass by 97–98% at concentrations of 2–10 mg/mL. The MIC and MBC values of (+)-endo-borneol were 2.5 and 5.0 mg/mL, respectively. Gene expression analysis demonstrated that subinhibitory concentrations of (+)-endo-borneol modulated the transcription of gtfB and yycF, indicating activation of bacterial regulatory responses. Molecular docking revealed favorable binding of (+)-endo-borneol to biofilm-related protein targets. These findings demonstrate that (+)-endo-borneol is a promising natural antibiofilm compound with potential application in the development of novel preventive and therapeutic oral healthcare products targeting S. mutans biofilms. Full article
(This article belongs to the Section Horticultural Science and Ornamental Plants)
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16 pages, 1036 KB  
Article
Patchouli Alcohol as a Potential Anti-Cariogenic Compound Targeting Streptococcus mutans
by Qianying Chen, Chong Feng, Zhimin Zhao, Depo Yang and Wenzhe Yang
Molecules 2026, 31(15), 2577; https://doi.org/10.3390/molecules31152577 - 24 Jul 2026
Viewed by 259
Abstract
Patchouli alcohol, a natural tricyclic sesquiterpene isolated from Pogostemon cablin, exhibits promising antimicrobial properties, yet its activity against Streptococcus mutans (S. mutans), a major cariogenic bacterium associated with dental caries, has not been characterized. This study determined the minimum inhibitory [...] Read more.
Patchouli alcohol, a natural tricyclic sesquiterpene isolated from Pogostemon cablin, exhibits promising antimicrobial properties, yet its activity against Streptococcus mutans (S. mutans), a major cariogenic bacterium associated with dental caries, has not been characterized. This study determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of patchouli alcohol against S. mutans to be 40 and 80 μg/mL, respectively. A series of phenotypic assays showed that patchouli alcohol delayed bacterial growth and culture acidification, reduced extracellular polysaccharide production, and decreased the biomass and metabolic activity of established S. mutans biofilms. Scanning electron microscopy showed treatment-associated changes in the surface morphology of S. mutans, with more evident deformation at MIC and 2MIC. Real-time quantitative PCR showed that sub-MIC treatment (20 μg/mL) significantly downregulated virulence genes associated with adhesion (gbpB and spaP), EPS synthesis (gtfB, gtfC, gtfD, and ftf), acid production (ldh, atpF, and atpD), and the two-component regulatory and quorum sensing systems (vicK, vicR, and luxS). These results suggest that patchouli alcohol may serve as a potential natural anti-cariogenic candidate targeting S. mutans-associated virulence traits under in vitro conditions. Full article
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28 pages, 11962 KB  
Article
Bioactive Silver Nanoparticles Synthesized Using Endophytic Bacillus subtilis CG1 and Their Antimicrobial and Antibiofilm Potential Against Drug-Resistant Pathogens
by Ghaida Saud Aljohani and Saleh H. Salmen
Pharmaceuticals 2026, 19(7), 1102; https://doi.org/10.3390/ph19071102 - 17 Jul 2026
Viewed by 553
Abstract
Background/Objectives: The study addresses the global health challenge posed by multidrug-resistant (MDR) pathogens, highlighting the urgent need for alternative antimicrobial solutions. This study investigated the in vitro antimicrobial and antibiofilm potential of endophytic mediated-synthesized silver nanoparticles (AgNPs). Methods: An endophytic bacterium was isolated [...] Read more.
Background/Objectives: The study addresses the global health challenge posed by multidrug-resistant (MDR) pathogens, highlighting the urgent need for alternative antimicrobial solutions. This study investigated the in vitro antimicrobial and antibiofilm potential of endophytic mediated-synthesized silver nanoparticles (AgNPs). Methods: An endophytic bacterium was isolated from the medicinal plant Commiphora gileadensis in Saudi Arabia and identified as Bacillus subtilis CG1 through 16S rRNA gene sequencing. The bacterium was utilized for the green synthesis of AgNPs, as confirmed by Ultraviolet-visible (UV–Vis) spectroscopy. AgNPs characterization was done using Fourier-transform infrared (FTIR) spectroscopy, Transmission and scanning electron microscopy (TEM and SEM), energy-dispersive X-ray spectroscopy (EDX), and dynamic light scattering (DLS). The antimicrobial efficacy of the fabricated AgNPs was tested against eight clinically relevant pathogens using standard in vitro assays such as the agar disk diffusion method, minimum inhibitory concentration (MIC), minimum bactericidal and fungicidal concentrations (MBC and MFC). Additionally, AgNPs were tested for antibiofilm activity against P. aeruginosa and S. epidermidis. Tested pathogens included Methicillin-Resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Candida auris, Candida albicans, and Candida tropicalis. The antibiofilm efficacy was tested using the Crystal violet assay. Results: UV–Vis spectroscopy confirmed AgNP formation with a characteristic absorption peak at 412 nm. FTIR analysis identified the presence of hydroxyl, nitrile, and alkyne functional groups, which are involved in nanoparticle reduction and stabilization. TEM and SEM revealed predominantly spherical AgNPs with sizes ranging from 17 to 72 nm, while EDX confirmed silver as the major elemental component. DLS analysis showed a Z-average particle size of 113.9 ± 67.75 nm and a zeta potential of −24.2 mV. The synthesized AgNPs exhibited concentration-dependent antimicrobial activity, producing inhibition zones of 10–20 mm at 240 µg/mL. MIC values ranged from 6.25 to 25 µg/mL, whereas MBC and MFC values ranged from 6.25 to 50 µg/mL and 25 to 100 µg/mL, respectively. Moreover, bacterial growth kinetics analysis demonstrated a concentration-dependent inhibition of growth by AgNPs at MIC and sub-MIC concentrations. Additionally, AgNPs demonstrated significant antibiofilm activity against P. aeruginosa and S. epidermidis.Conclusions: Overall, B. subtilis CG1-mediated AgNPs exhibited promising physicochemical properties and antimicrobial and antibiofilm activities, suggesting their potential as alternatives for combating resistant and biofilm-associated infections. Full article
(This article belongs to the Section Medicinal Chemistry)
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15 pages, 12183 KB  
Article
Antibacterial Activity of Berberine Against Aeromonas hydrophila and Associated Transcriptional Reprogramming
by Lianshou Lu, Jian Zhang, Xianming Liang and Dongkai Wang
Biology 2026, 15(14), 1177; https://doi.org/10.3390/biology15141177 - 17 Jul 2026
Viewed by 398
Abstract
Berberine (BBR), a plant-derived isoquinoline alkaloid, exhibits broad-spectrum antibacterial activity, but its molecular mechanisms against Aeromonas hydrophila remain unclear. This study investigated the antibacterial action and underlying mechanisms of BBR against A. hydrophila through integrated phenotypic assays and transcriptomic analysis. BBR showed notable [...] Read more.
Berberine (BBR), a plant-derived isoquinoline alkaloid, exhibits broad-spectrum antibacterial activity, but its molecular mechanisms against Aeromonas hydrophila remain unclear. This study investigated the antibacterial action and underlying mechanisms of BBR against A. hydrophila through integrated phenotypic assays and transcriptomic analysis. BBR showed notable antibacterial activity with a minimum inhibitory concentration (MIC) of 2.5 g/L. Treatment at a sub-inhibitory concentration (1/2 MIC) severely compromised cell membrane integrity, evidenced by increased leakage of alkaline phosphatase (AKP) and β-galactosidase (β-GAL). Transmission electron microscopy (TEM) revealed ultrastructural damage including plasmolysis and membrane rupture. RNA-seq analysis identified 740 differentially expressed genes (DEGs). Crucially, BBR extensively downregulated core energy metabolism and catabolic pathways, including the TCA cycle, fatty acid β-oxidation, and amino acid degradation. Concurrently, genes associated with flagellar assembly and DNA repair were upregulated. These findings reveal that BBR exerts its antibacterial effect via a multi-target mechanism involving direct physical damage to the cell envelope and the suppression of central metabolism. This study elucidates the antibacterial effects of BBR against A. hydrophila and provides a foundation for its potential use as an eco-friendly agent in aquaculture. Full article
(This article belongs to the Section Microbiology)
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16 pages, 1874 KB  
Article
Protein Expression Profiles of Antiseptic-Adapted Escherichia coli
by David L. Auer, Uemmuehan Akyol, Denise Muehler, Konstantin J. Scholz, Karl-Anton Hiller, Tim Maisch, Wolfgang Buchalla, Ali Al-Ahmad and Fabian Cieplik
Microorganisms 2026, 14(7), 1533; https://doi.org/10.3390/microorganisms14071533 - 14 Jul 2026
Viewed by 339
Abstract
Repeated exposure to subinhibitory concentrations of antiseptics may lead to reduced susceptibility or resistance and potentially promote cross-resistance to antibiotics. However, the underlying molecular mechanisms remain incompletely understood. This study investigated whether antiseptic-adapted Escherichia coli strains exhibit altered protein expression profiles compared with [...] Read more.
Repeated exposure to subinhibitory concentrations of antiseptics may lead to reduced susceptibility or resistance and potentially promote cross-resistance to antibiotics. However, the underlying molecular mechanisms remain incompletely understood. This study investigated whether antiseptic-adapted Escherichia coli strains exhibit altered protein expression profiles compared with wild-type (WT) E. coli. Protein expression was analysed in E. coli strains previously adapted over ten passages to subinhibitory concentrations of chlorhexidine (CHX), cetylpyridinium chloride (CPC), and benzalkonium chloride (BAC). WT bacteria were exposed to sub-minimum inhibitory concentrations (sub-MICs) of antiseptics for 3 h to induce stress. Untreated WT and heat-shocked WT E. coli (42 °C, 2 h) served as controls. Protein expression profiles were assessed using SDS-PAGE and Western blotting targeting stress-associated proteins. SDS-PAGE demonstrated altered protein expression patterns in antiseptic-adapted strains, including differences in band intensities and additional protein bands. Western blot analysis showed increased DnaK and GroEL expression with reduced LexA levels in heat-shocked WT bacteria, whereas RecA remained largely unchanged. Antiseptic-adapted strains exhibited increased DnaK, GroEL, and OmpF expression together with reduced LexA and RecA expression. These findings indicate that adaptation to antiseptics involves complex mechanisms among multiple proteins rather than a single adaptive mechanism. Full article
(This article belongs to the Special Issue Bacterial Genetics and Antibiotic Resistances)
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16 pages, 4017 KB  
Article
Evaluation of Antimicrobial Peptide–Antibiotic Combination Treatment for Tackling Ocular and Systemic Staphylococcus aureus Infections
by Eman Khalid Barahim, Ella P. Smith, Sheau Ting Yong, Thet Tun Aung, Rajamani Lakshminarayanan, Imran Mohammed, Harminder S. Dua, Graham R. Wallace, Jose R. Hombrebueno, Saaeha Rauz and Darren S. J. Ting
Int. J. Mol. Sci. 2026, 27(12), 5573; https://doi.org/10.3390/ijms27125573 - 20 Jun 2026
Viewed by 540
Abstract
Staphylococcus aureus is a leading cause of bacterial keratitis and antimicrobial resistance-associated death globally. This study aimed to evaluate the efficacy of CaD23, a human-derived hybrid antimicrobial peptide (AMP), in combination with antibiotics in treating S. aureus infections. The efficacy of CaD23 and [...] Read more.
Staphylococcus aureus is a leading cause of bacterial keratitis and antimicrobial resistance-associated death globally. This study aimed to evaluate the efficacy of CaD23, a human-derived hybrid antimicrobial peptide (AMP), in combination with antibiotics in treating S. aureus infections. The efficacy of CaD23 and six medically important antibiotics (amikacin, cefuroxime, chloramphenicol, fosfomycin, vancomycin and levofloxacin) was examined against six strains of methicillin-sensitive and methicillin-resistant S. aureus using a minimum inhibitory concentration (MIC) assay. CaD23–antibiotic interactions were evaluated using checkerboard and time–kill kinetics assays. 3,3′-dipropylthiadicarbocyanine iodide (DiSC3,5) cytoplasmic membrane depolarisation assay was performed to examine the mechanism of action. Overall, CaD23 exhibited good efficacy against all MSSA and MRSA (MIC = 16–32 μg/mL [6.7–13.3 μM]). Of 20 peptide–antibiotic–organism combinations, 19 (95%) combinations demonstrated positive interactions, with six (31.6%) and 13 (68.4%) exhibiting synergistic (FICI = 0.293–0.412) and additive effects (FICI = 0.521–0.890), respectively. CaD23 was able to achieve complete bacterial eradication significantly faster than cefuroxime and levofloxacin (15 min vs. 8–24 h). When used at a sub-MIC concentration, CaD23 could accelerate the killing of S. aureus of cefuroxime from 8–24 h to within 1 h and enhance the activity of levofloxacin by 90%. CaD23 was shown to rapidly depolarise the inner membrane of S. aureus within seconds of the treatment. In conclusion, CaD23–antibiotic combination therapy serves as a useful strategy for tackling drug-resistant ocular and systemic S. aureus infections. Full article
(This article belongs to the Special Issue Antimicrobial and Antiviral Peptides: 2nd Edition)
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16 pages, 2051 KB  
Article
Sub-Minimum Inhibitory Concentrations of Amoxicillin Modulate Biofilm Formation and the Expression of Biofilm-Associated Genes in Enterococcus faecalis
by Desiye T. Tegegne, Sylwia Banaszkiewicz, Jacek Bania and Błażej Poźniak
Molecules 2026, 31(12), 1986; https://doi.org/10.3390/molecules31121986 - 6 Jun 2026
Viewed by 596
Abstract
Background: Enterococcus faecalis is one of the most frequent causes of catheter-associated urinary tract infections, largely due to its ability to form biofilms on indwelling urinary catheter surfaces, which enhance bacterial persistence and antimicrobial tolerance. Sub-minimum inhibitory concentrations (sub-MICs) of antimicrobials frequently [...] Read more.
Background: Enterococcus faecalis is one of the most frequent causes of catheter-associated urinary tract infections, largely due to its ability to form biofilms on indwelling urinary catheter surfaces, which enhance bacterial persistence and antimicrobial tolerance. Sub-minimum inhibitory concentrations (sub-MICs) of antimicrobials frequently occur in clinical settings, and growing evidence suggests that such suboptimal exposures can induce bacterial biofilm formation. We hypothesized that exposure to sub-MICs of amoxicillin, ciprofloxacin, and nitrofurantoin, antimicrobials commonly employed in the treatment of urinary tract infections, would enhance the biofilm-forming capacity of E. faecalis strains. Objective: To investigate the effects of sub-MICs of amoxicillin, ciprofloxacin, and nitrofurantoin on biofilm formation and biofilm-associated gene expression. The study focused on key biofilm-related genes, including those encoding aggregation substance protein (asa1), collagen adhesin (ace), E. faecalis surface protein (esp), gelatinase (gelE), cytolysin activator A (cylA), endocarditis antigen A (efaA), and the endocarditis- and biofilm-associated pili subunit A (ebpA) in E. faecalis. Methods: Two strains, E. faecalis ATCC 29212 and strain 54, were exposed to 1/8× and 1/4× MIC of amoxicillin, ciprofloxacin, and nitrofurantoin in either artificial urine medium (AUM) or tryptone soya broth (TSB). Bacterial growth kinetics were monitored by optical density measurements, while biofilm formation was quantified using a microtiter plate biofilm assay. The expression of biofilm-associated genes was analyzed using quantitative reverse transcription PCR (RT-qPCR) at 24 and 48 h following exposure to sub-MICs of amoxicillin under flow conditions mimicking the urinary tract milieu. Results: Exposure to sub-MICs of the three antimicrobials did not significantly affect bacterial growth in either strain or culture medium. Sub-MICs of amoxicillin significantly enhanced biofilm formation, with the most pronounced effect observed at 1/4× MIC in both AUM and TSB. In contrast, ciprofloxacin and nitrofurantoin exerted inhibitory effects on biofilm formation across both media. Gene expression analysis demonstrated time- and strain-dependent responses to amoxicillin exposure. E. faecalis ATCC 29212 exhibited a moderate, coordinated upregulation of adhesion- and biofilm-associated genes, particularly at 48 h. By comparison, E. faecalis strain 54 showed a stronger and more dynamic transcriptional response, characterized by early and sustained induction of key biofilm-related genes, including esp and gelE, as well as a pronounced late upregulation of ebpA. Conclusions: These findings emphasize the importance of maintaining therapeutically effective antimicrobial concentrations, as sub-inhibitory amoxicillin exposure may promote biofilm-associated persistence and potentially compromise treatment efficacy. Full article
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18 pages, 3906 KB  
Article
Differential Effects of Low-Intensity Pulsed Ultrasound and Antifungals on Candida albicans and Candida glabrata: Implications for Drug Efficacy
by Sichen Liu, James Townley, Amir Seyedmousavi and Joseph A. Frank
J. Fungi 2026, 12(6), 399; https://doi.org/10.3390/jof12060399 - 30 May 2026
Viewed by 599
Abstract
Invasive fungal infections pose significant clinical challenges, owing to limited antifungal efficacy and poor tissue drug penetration. This study investigated whether low-intensity pulsed ultrasound (LIPUS) could enhance the antifungal activity of sub-minimal inhibitory concentrations (sub-MICs) of amphotericin B (AmB) and micafungin (MFG) against [...] Read more.
Invasive fungal infections pose significant clinical challenges, owing to limited antifungal efficacy and poor tissue drug penetration. This study investigated whether low-intensity pulsed ultrasound (LIPUS) could enhance the antifungal activity of sub-minimal inhibitory concentrations (sub-MICs) of amphotericin B (AmB) and micafungin (MFG) against two strains from two phylogenetically distinct Candida species: Candida albicans and Candida glabrata. Growth inhibition was assessed following LIPUS (15 min, 50% duty cycle, 1 W/cm2) alone or in combination with sub-MIC antifungals. Time-kill assays and adenylate kinase (AK) release evaluated the cell viability and membrane integrity, respectively. LIPUS transiently but markedly delayed C. albicans growth and enhanced the antifungal effects of both AmB and MFG at sub-MIC levels. The combination of LIPUS and ¼ MIC AmB reduced CFU counts by over 3 log at 12 h and induced higher AK release compared to controls, indicating membrane leakage. In contrast, Candida glabrata showed minimal susceptibility to LIPUS, with low AK release and mitigation of the fungistatic effects of sub-MIC MFG. Our study demonstrates that LIPUS can potentiate sub-MIC antifungals against C. albicans but may have the opposite effect in C. glabrata. This strain-specific variation in response to LIPUS underscores the need for further investigation before LIPUS can be considered as a treatment-enhancement strategy. Full article
(This article belongs to the Section Fungal Pathogenesis and Disease Control)
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16 pages, 4186 KB  
Article
From Peril to Poise: An Organic Acid Strategy to Attenuate Pseudomonas fluorescens Virulence in Shrimp and Fish Infection Models
by Iulia Bundurus, Igori Balta, Ioan Pet, Lavinia Stef, Stefan Kalinović, Ana-Maria Imbrea, Diana Marcu, Claudia Loredana Crista, Sorin Morariu and Nicolae Corcionivoschi
Fishes 2026, 11(6), 327; https://doi.org/10.3390/fishes11060327 - 30 May 2026
Viewed by 615
Abstract
This study evaluated the anti-virulence effect of AuraAqua (Aq), a natural mixture of organic acids, against Pseudomonas. fluorescens. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Aq against P. fluorescens were 0.5% and 1% (v/v), [...] Read more.
This study evaluated the anti-virulence effect of AuraAqua (Aq), a natural mixture of organic acids, against Pseudomonas. fluorescens. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Aq against P. fluorescens were 0.5% and 1% (v/v), respectively. Growth curve analysis confirmed concentration-dependent inhibition of planktonic growth, while sub-inhibitory Aq (0.25%; 1/2 MIC) significantly reduced biofilm formation. Rhodamine-based assays revealed membrane depolarisation at both 0.25% and 0.5% Aq, with decreased intracellular protein levels, indicating impaired membrane integrity under the tested conditions. In fibronectin adherence assays, the presence of Aq during bacterial contact markedly reduced adherence, whereas short pre-treatment alone produced limited, non-persistent effects, suggesting that continuous exposure is required to interfere with host matrix binding. Supernatants and lysates from Aq-exposed P. fluorescens induced lower extracellular protease activity in a concentration-dependent manner and mitigated P. fluorescens-induced cytotoxicity in primary shrimp (SGP) and tilapia (TGP) gut cells, as measured by lactate dehydrogenase (LDH) release after exposure to bacterial supernatants and lysates. Aq treatment was associated with decreased P. fluorescens internalisation into SGP and TGP cells. Collectively, these data show that Aq exerts multi-target inhibitory and virulence-attenuating effects on P. fluorescens, supporting its potential use in aquaculture environments. Full article
(This article belongs to the Special Issue Effects of Dietary Ingredients on Fish Nutrition and Health)
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22 pages, 5374 KB  
Article
Matrine Restores Porcine-Origin β-Lactam-Resistant Escherichia coli to Cefepime and Cefquinome: Association with Impaired Biofilm Formation and β-Lactamase Production
by Bo Yang, Wen Yang, Bingyan Hu, Jingchao Zhao, Hui Deng, Lingxian Yi, Penghua Jian, Zelin Hong and Daojin Yu
Antibiotics 2026, 15(5), 494; https://doi.org/10.3390/antibiotics15050494 - 14 May 2026
Viewed by 413
Abstract
Background: The in vivo efficacy and mechanisms of matrine (MT) in reversing β-lactam resistance in E. coli remain unclear. Methods: β-lactam-resistant E. coli strains were treated with MT both in vitro and in a murine intestinal colonization model. Phenotypic changes (MIC, morphology, [...] Read more.
Background: The in vivo efficacy and mechanisms of matrine (MT) in reversing β-lactam resistance in E. coli remain unclear. Methods: β-lactam-resistant E. coli strains were treated with MT both in vitro and in a murine intestinal colonization model. Phenotypic changes (MIC, morphology, growth, biofilm, β-lactamase) were evaluated, and transcriptomic profiles were analyzed. Results: MT at sub-inhibitory concentrations significantly and concentration-dependently reduced the MICs of β-lactam-resistant E. coli strains by 2- to 32-fold in vitro. This reduction was also confirmed in vivo, and its magnitude became more pronounced as the number of doses increased. MT treatment dispersed bacterial aggregates and dissipated extracellular matrix, but did not alter the morphology of individual bacteria. At concentrations above 1024 μg/mL, MT significantly inhibited bacterial growth; lower concentrations (≤512 μg/mL) had no effect. Notably, MT inhibited biofilm formation and β-lactamase production both in vitro and in vivo. Conclusions: MT restored the susceptibility of β-lactam-resistant E. coli to cefepime and cefquinome. This effect was associated with suppression of biofilm formation and β-lactamase production, which correlated with the downregulation of key genes (ycgR, pgaB, pgaD, blaTEM and blaCTX-M). Full article
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26 pages, 4603 KB  
Article
Antimicrobial and Antibiofilm Activities of Glycyl–Histidine and Methionyl–Glycine Dipeptides: In Vitro and Molecular Docking Studies
by Gulcan Sahal, Tuğçe Deniz Karaca, Yusuf Sert, Meltem Maras and Alev Doğan
Molecules 2026, 31(10), 1641; https://doi.org/10.3390/molecules31101641 - 13 May 2026
Viewed by 496
Abstract
The increasing prevalence of antimicrobial resistance and biofilm-associated infections has intensified the search for alternative anti-infective strategies. Short peptide-based molecules have attracted growing interest due to their structural simplicity, biocompatibility, and multifunctional biological properties. In this study, the antimicrobial and antibiofilm activities of [...] Read more.
The increasing prevalence of antimicrobial resistance and biofilm-associated infections has intensified the search for alternative anti-infective strategies. Short peptide-based molecules have attracted growing interest due to their structural simplicity, biocompatibility, and multifunctional biological properties. In this study, the antimicrobial and antibiofilm activities of two dipeptides, glycyl–histidine and methionyl–glycine, were evaluated against reference microorganisms, including Escherichia coli ATCC 35218, Klebsiella pneumoniae MTCC 109, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, and Candida albicans ATCC 10231. Antimicrobial activity was determined using broth microdilution and disk diffusion assays, while antibiofilm effects were evaluated at sub-inhibitory concentrations using a crystal violet-based biofilm inhibition assay supported by light microscopy. In addition, the electronic structure, binding interactions, and pharmacokinetic properties of the dipeptides were investigated using integrated density functional theory (DFT), molecular docking, and ADME analyses. Glycyl–histidine exhibited antimicrobial activity against all tested bacterial strains (MIC: 12.5 mg/mL) and against C. albicans (MIC: 50 mg/mL), whereas methionyl–glycine showed no detectable antimicrobial activity. Both dipeptides demonstrated microorganism-dependent antibiofilm effects, with glycyl–histidine consistently displaying stronger activity. Notably, glycyl–histidine reduced biofilm formation by up to 88% in K. pneumoniae and by 54% in P. aeruginosa at 0.5 × MIC. In C. albicans, biofilm formation decreased by 22–39% under conditions where the reference antibiotic solution showed no antibiofilm effect. Computational analyses supported the experimental findings and provided molecular-level insights into the antimicrobial and antibiofilm potential of glycyl–histidine. Overall, these results identify glycyl–histidine as a promising anti-infective dipeptide and highlight its potential as a promising building block for the development of novel anti-infective agents. Full article
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21 pages, 12330 KB  
Article
In Vitro Antifungal and Wound-Healing Potential of Ferulago cassia and Ferulago silaifolia Essential Oils in Skin Candidiasis
by Carolina Furtado, Manuel González-Vázquez, Ceyda Sibel Kılıç, Lígia Salgueiro and Mónica Zuzarte
Antibiotics 2026, 15(5), 471; https://doi.org/10.3390/antibiotics15050471 - 6 May 2026
Viewed by 777
Abstract
Background/Objectives: Skin candidiasis is a key contributor to chronic, non-healing wounds, largely due to persistent microbial infections. Candida species can colonize the skin, form protective biofilms, and interfere with enzyme activity, leading to extracellular matrix degradation, changes in pigmentation, and impaired wound healing. [...] Read more.
Background/Objectives: Skin candidiasis is a key contributor to chronic, non-healing wounds, largely due to persistent microbial infections. Candida species can colonize the skin, form protective biofilms, and interfere with enzyme activity, leading to extracellular matrix degradation, changes in pigmentation, and impaired wound healing. The rising prevalence of antifungal resistance challenges its management, underscoring the need for more effective antifungal therapies. Therefore, this study aimed to assess the antifungal effects and wound-healing potential of essential oils (EOs) from Ferulago spp. Methods: The antifungal activity of the EOs from five Ferulago species was evaluated against Candida spp. and Cryptococcus neoformans. The most active EOs were further investigated for their effects on C. albicans virulence factors, including germ tube formation, as well as biofilm formation and disruption. These effects were assessed using microscopic observation, XTT reduction assay, and crystal violet and safranin stainings. The wound-healing potential of the EOs was evaluated using the scratch-wound assay on fibroblasts and keratinocytes. Additionally, the effect on tyrosinase and elastase activity, was also investigated. Results:F. silaifolia and F. cassia essential oils showed fungicidal activity against Candida spp. and Cryptococcus neoformans. F. silaifolia displayed greater potency, with lower MIC and MLC values. Both oils inhibited key C. albicans virulence factors at sub-MIC concentrations. F. silaifolia EO was more effective in preventing biofilm formation whereas F. cassia EO showed notable tyrosinase inhibitory effect. Conclusions: These findings align with traditional uses and suggest that F. silaifolia and F. cassia EOs exhibit antifungal activity alongside properties associated with wound healing, supporting their potential as topical antifungal agents and thereby justifying further investigation. Full article
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Article
Hemolytic Activity of Vaginal Candida albicans Isolates and Antifungal Effects of Quinalizarin with Hemolysis Modulation
by Monika Janeczko and Elżbieta Kochanowicz
Pathogens 2026, 15(4), 401; https://doi.org/10.3390/pathogens15040401 - 8 Apr 2026
Cited by 1 | Viewed by 629
Abstract
This study evaluated the hemolytic activity of Candida albicans isolates from the female reproductive tract and investigated the in vitro effects of quinalizarin on fungal growth, hemolysis, and ECE1 expression. Ninety-four clinical C. albicans isolates and three ATCC reference strains were analyzed. Hemolytic [...] Read more.
This study evaluated the hemolytic activity of Candida albicans isolates from the female reproductive tract and investigated the in vitro effects of quinalizarin on fungal growth, hemolysis, and ECE1 expression. Ninety-four clinical C. albicans isolates and three ATCC reference strains were analyzed. Hemolytic activity was quantified in culture supernatants and normalized per 107 cells. Antifungal susceptibility and the effect of quinalizarin on hemolysis were assessed using broth microdilution and hemolysis assays. Expression of the ECE1 gene was evaluated by quantitative real-time PCR in three selected hemolytic strains. Drug interactions between quinalizarin and fluconazole were determined using the fractional inhibitory concentration index (FICI). Among the 97 tested strains, 78 exhibited hemolytic activity with variable intensity. Quinalizarin demonstrated antifungal activity, with MIC values ranging from 2 µg/mL to 256 µg/mL, and showed synergistic effects with fluconazole in selected strains. Exposure to quinalizarin at subinhibitory concentrations reduced ECE1 transcript levels to 22.8–73.6% of controls (p < 0.05) in the analyzed strains. However, the phenotypic effect on hemolysis was limited, with residual activity remaining high: 82% (p < 0.05), 93.7% (p < 0.05), and 83% (p < 0.05) relative to untreated controls in C. albicans ATCC 10231, ATCC 90028, and a clinical isolate, respectively. FICI analysis confirmed synergistic interactions between quinalizarin and fluconazole. This preliminary in vitro study highlights the need for further investigation into the relationship between ECE1 expression, candidalysin-mediated damage, and the antifungal potential of quinalizarin. Full article
(This article belongs to the Special Issue Insights into Fungal Infections)
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