Background: The escalation of multidrug-resistant (MDR) Klebsiella pneumoniae infections poses a severe global health threat, necessitating the exploration of alternative therapeutic strategies such as drug repurposing. This study aims to investigate the intrinsic antibacterial activity of the antidiabetic drug metformin and its adjuvant potential when combined with conventional antibiotics against K. pneumoniae. Materials and Methods: The antimicrobial effects of metformin were evaluated against the reference strain K. pneumoniae ATCC 700603 and an MDR clinical isolate obtained from an intensive care unit. Minimum Inhibitory Concentration (MIC) values were determined using the microdilution method. Interaction studies between metformin and three antibiotics (Levofloxacin, Amikacin, and Ceftazidime) were conducted using the checkerboard assay. The results were interpreted based on the Fractional Inhibitory Concentration Index (FICI). Results: Metformin monotherapy exhibited weak intrinsic antibacterial activity (MIC ≥ 500 µg/mL) against both the reference strain and the clinical isolate. In combination assays, metformin demonstrated an antagonistic effect with Levofloxacin, while its interactions with Amikacin and Ceftazidime were classified as indifferent. The observed antagonism with Levofloxacin is attributed to metformin’s antioxidant properties, which likely mitigate the oxidative stress required for the bactericidal action of fluoroquinolones. Furthermore, the lack of synergy with Amikacin suggests that metformin-induced disruption of the Proton Motive Force (PMF) may hinder the intracellular uptake of aminoglycosides. Conclusion: The findings indicate that metformin is ineffective as a standalone antibacterial agent against K. pneumoniae. Moreover, its adjuvant potential is highly dependent on the antibiotic class and strain-specific resistance mechanisms. Contrary to some reports of synergy, this study highlights the risk of antagonism, particularly with fluoroquinolones. Further standardized mechanistic studies are required to define the specific therapeutic windows for metformin as an antimicrobial adjuvant.

Background/Objectives: Atopic dermatitis (AD) is associated with gut dysbiosis linked to early-life antibiotic use and Staphylococcus aureus colonization. Gum Arabic (GA), a prebiotic, may modulate this dysbiosis and influence AD-related microbial balance. This study evaluated whether GA could support AD-associated probiotics-Lactobacillus casei, Bifidobacterium bifidum, and Bifidobacterium infantis-under amoxicillin- or azithromycin-containing conditions, examined the response of S. aureus under the same screening conditions, and developed GA-phospholipid-based semisolid carriers for topical application. Methods: Probiotic strains were cultured with 1–5% GA in the presence and absence of antibiotics, and viable cell counts were assessed. Sixteen topical formulations containing propylene glycol or isopropyl myristate in a hydrogenated phosphatidylcholine base were prepared and screened for rheological properties and galactose release using in vitro release testing (IVRT) and HPLC-UV. Results: GA at 1–2% concentrations promoted probiotic growth in antibiotic-free conditions. GA preserved B. infantis viability under azithromycin exposure in this in vitro screening model. For S. aureus, numerical CFU differences were observed between antibiotic-only and GA-containing conditions; however, the present screening design was not intended to determine antibiotic interaction outcomes. Formulations F14 (2% GA + 7% IPM) and F15 (3% GA + 7% IPM) exhibited optimal spreadability. IVRT showed that 6 h cumulative galactose release varied by formulation (F6 > F10 > F14 > F15). Conclusions: GA demonstrated dose-dependent prebiotic activity and preserved B. infantis viability under azithromycin exposure in this in vitro screening model. For S. aureus, the observed CFU differences between antibiotic-only and GA-containing conditions should be considered exploratory only and do not allow for conclusions regarding interference with antibiotic efficacy. Optimized GA-HPC systems with suitable rheological and release characteristics represent promising candidates for further preclinical investigation.

In this study, the antimicrobial effects of essential oils obtained from 7 different plants (Lavandula angustifolia, Lavandula intermedia, Cupressus sempervirens, Syzygium aromaticum, Salvia officinalis, Allium sativum, Pimpinella anisum) and their combinations with Lavandula angustifolia, were investigated against 11 pathogenic bacteria (Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 29213, Staphylococcus haemolyticus ATCC 43252, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC 700603, Escherichia coli ATCC NRRLB 3704, Acinetobacter baumannii ATCC 19606, Bacillus subtilis ATCC 6633, Proteus vulgaris ATCC 13315, Enterococcus faecalis ATCC 29212, Aeromonas hydrophila ATCC 95080). The synergistic effect of essential oils and their combinations with L. angustifolia were determined using the agar well diffusion method. Each essential oil was subjected to gas chromatography analysis in order to identify their chemical compositions. According to the results, generally all essential oils exhibited the greatest inhibition zones for Gram-positive bacteria than for Gram-negative bacteria. Among the essential oil combinations, the highest synergistic effect (166.7%) was obtained in L. angustifolia-P.anisum combination against P. aeruginosa ATCC 27853. Additionally, the L. angustifolia-S. aromaticum combination was observed to exhibit a synergistic effect on 5 bacteria (K. pneumoniae, E. coli, E. faecalis, S. haemolyticus and A. hydrophila). These findings suggest that L. angustifolia combined with specific essential oils particularly L. intermedia and S. aromaticum may serve as promising natural antimicrobial agents, offering enhanced inhibitory activity against clinically important bacterial pathogens.

Across different regions of the world, plants have long been valued for their wide range of functional properties. Aromatic plants, in particular, are cultivated to obtain natural compounds used in cosmetic scenting, food enhancement, and preservation. Within this category, species belonging to the Asteraceae family have gained increasing attention in recent years due to their expanding relevance in numerous applied disciplines. The objective of this study was to evaluate the antibacterial and antifungal potential of different solvent extracts (n-hexane, ethyl acetate, and methanol) and an infusion of Centaurea iberica L. against five bacterial (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Staphylococcus epidermidis ATCC 12228, Acinetobacter baumannii ATCC 19606, Pseudomonas aeruginosa ATCC 27853) and two yeast (Candida albicans ATCC 10231 and Candida parapsilosis ATCC 22019) strains using the microdilution method. The minimum inhibitory concentration (MIC) values for all tested microorganisms ranged between 78.125 and 5000 µg/mL. According to the results, all studied extracts exhibited stronger antifungal activity than antibacterial activity. Among them, the ethyl acetate extract demonstrated the most potent antifungal effect with MIC values between 78.125 and 156.25 µg/mL, whereas the infusion extract showed the weakest overall activity. In conclusion, further phytochemical investigations are required to identify the secondary metabolites responsible for these activities, which may contribute to the development of novel antifungal agents.

Candida species remain the most prevalent pathogens in nosocomial fungal infections. However, invasive infections caused by non-Candida opportunistic fungi, have emerged as a significant concern, particularly in immunocompromised patients. The widespread use of antifungal agents in intensive care units (ICUs) further accelerates the development of resistant species. This retrospective study aimed to evaluate the species distribution and antifungal susceptibility of fungi isolated from various clinical samples at a university hospital in Istanbul during the Corona virus Disease 19 (COVID-19) pandemic (2020–2022). Isolates were identified using germ tube testing and the VITEK 2 Compact® system. Susceptibility was tested against fluconazole, voriconazole, caspofungin, micafungin, amphotericin B, and flucytosine. A total of 279 isolates were obtained from 243 patients, with 66% (n=185) originating from the ICU. Urine was the most frequent specimen type (48%). Candida species accounted for 94% (n=264) of the isolates, while 6% (n=15) were non-Candida species. The findings revealed that Candida albicans exhibited the highest resistance to voriconazole (12.3%). Notably, 37.5% of Cryptococcus laurentii isolates displayed elevated minimum inhibitory concentration (MIC) values to both caspofungin and micafungin. Furthermore, Trichosporon asahii demonstrated concerningly high MICs in 71.4% of the isolates to fluconazole, caspofungin, and micafungin. Increasing fungal infection frequency, rising Candida resistance, and elevated MIC profiles in rare species pose critical clinical challenges. Continuous monitoring of local susceptibility and MIC patterns is essential to mitigate the high mortality and morbidity associated with fungal pathogens during and after pandemic periods. These results highlight the urgent need for surveillance.

Inspired by the medicinally relevant stilbene scaffold, a series of six electronically tuned benzylidene-based Schiff base derivatives were designed, synthesized, and characterized by FT-IR, ¹H NMR, ¹³C NMR, and ESI-MS analyses. The biological properties of the synthesized compounds were investigated through antioxidant, enzyme inhibitory, and antimicrobial assays, while molecular docking and density functional theory (DFT) calculations were performed to rationalize the experimental findings and structure-activity relationships. Compounds 3 and 6 exhibited the strongest antioxidant activities, particularly in ABTS, CUPRAC, FRAP, phosphomolybdenum, and metal-chelating assays. Compounds 1–3 and 5 demonstrated measurable α-glucosidase inhibitory activity, although they were less potent than acarbose, whereas compounds 1 and 2 showed the highest tyrosinase inhibition within the synthesized series. Antimicrobial evaluation revealed moderate activity across the series, with compound 3 displaying relatively higher antimicrobial activity within the synthesized series. Docking studies demonstrated favorable interactions within enzyme active sites, while DFT calculations provided insights into electronic properties and molecular reactivity. As a result, the investigated substitution patterns were associated with differences in biological activity within the synthesized series, with compound 3 showing relatively favorable activity in selected assays and warranting further investigation.