Sandra Hojda

The global rise of antimicrobial resistance represents a major challenge to public health and highlights the urgent need for the discovery of new antibacterial agents. Xanthones, characterized by a rigid dibenzo-γ-pyrone scaffold, have emerged as promising candidates owing to their broad structural diversity and ability to interact with multiple biological targets. This review provides examples of natural, semisynthetic, and synthetic xanthone derivatives investigated for their antimicrobial potential. Natural xanthones and their structural diversity are first discussed, followed by an analysis of semisynthetic and synthetic derivatives developed to overcome the structural limitations imposed by natural biosynthetic pathways and to improve antimicrobial activity. Particular attention is devoted to structure–activity relationships, including the effects of hydroxylation, methoxylation, alkylation, halogenation, and the position of substituents on antibacterial potency. The review further critically evaluates the factors that may limit the translation of promising in vitro findings into therapeutic applications, including limited mechanistic understanding, physicochemical properties, selectivity, toxicity, and the scarcity of standardized experimental approaches. Collectively, the available evidence supports xanthone derivatives as a valuable and versatile scaffold for the development of new antimicrobial candidates, while also highlighting the substantial work required to advance these compounds toward practical therapeutic applications.

To bridge the clinical and methodological gap created by Poland’s widespread OTC use of furazidin in empirical urinary tract infections (UTIs) management versus EUCAST’s reliance on nitrofurantoin for susceptibility testing, by comparing their activity against E. coli isolates and identifying nfsA mutations associated with reduced nitrofuran susceptibility. Thirty-three E. coli isolates were obtained from outpatient urine samples. MICs for furazidin and nitrofurantoin were determined using broth microdilution, and MIC₅₀/MIC₉₀ values were calculated. Isolates with MIC ≥ 8 µg/ml underwent nfsA detection and Sanger sequencing of the examined nfsA gene. This analysis was performed as a targeted, exploratory assessment of genotype-phenotype associations, with results interpreted according to current EUCAST methodological standards. Furazidin showed higher in vitro activity than nitrofurantoin (mean MIC: 6.05 µg/ml vs. 10.46 µg/ml; MIC₅₀: 2 µg/ml vs. 4 µg/ml; MIC₉₀: 16 µg/ml vs. 32 µg/ml). The nfsA gene was detected in 75% of isolates with elevated MICs. Gene sequencing revealed nonsense and frameshift mutations leading to truncated nitroreductase, consistent with reduced susceptibility, although none of the isolates met EUCAST clinical resistance breakpoints. Nitrofurantoin MICs do not fully reflect the activity of furazidin, which is widely used in Poland and East European countries. These results underscore the need for region-specific evaluation of nitrofuran susceptibility and caution against extrapolating nitrofurantoin MICs to furazidin efficacy in clinical practice. Moreover, the findings highlight the need for improved standardization of nitrofuran susceptibility testing and further investigation of resistance mechanisms to guide optimal UTI therapy, particularly in outpatient populations where nitrofurans remain first-line empirical agents.

Multidrug-resistant bacteria, including vancomycin-resistant Enterococci (VRE), are a significant public health threat. This study aimed to perform molecular characterization of E. faecium and E. faecalis isolates with respect to glycopeptide and phenotypic resistance, and clonal relatedness. A total of 45 isolates (41 E. faecium, 4 E. faecalis) were obtained from clinical specimens collected at the University Hospital in Kraków, Poland. Isolates were screened on chromogenic media, identified by Matrix-Assisted Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and tested for antimicrobial susceptibility and the presence of vanA/vanB genes. Biofilm formation was assessed on culture media, and clonal relationships were determined using PFGE. Among the isolates, 86.7% harbored vanA and 13.3% vanB genes. E. faecium remained resistant mainly to ampicillin and teicoplanin, but susceptible to tigecycline and linezolid. E. faecalis showed partial susceptibility to ampicillin, tigecycline and linezolid, but frequent resistance to teicoplanin and reduced susceptibility to imipenem. Biofilm assessment revealed that 88.9% of isolates produced high biofilm levels. PFGE analysis identified several clonal groups among Enterococcus faecium, with clone A being the most prevalent (9 strains). The predominance of clonal strains and their robust biofilm production underscore the dissemination potential of VRE in hospital settings. High levels of antibiotic resistance highlight the limited therapeutic options available. Comprehensive preventive and control measures are essential to mitigate transmission of multidrug-resistant pathogens in healthcare environments. These findings provide recent epidemiological data on VRE circulation and highlight the clinical relevance of a dominant, biofilm-forming clonal lineage in a tertiary-care setting.

Implant-associated infections are a frequent complication of surgeries involving biomaterial implants. Staphylococcus and Enterococcus species are the leading causes of infections linked to bone-anchored and joint implants. To address this challenge, developing antibacterial coatings to prevent bacterial attachment and biofilm formation on biomaterials is critical. This study aimed to evaluate the antibacterial and antibiofilm properties of two biomaterial coatings: titanium nitride (TiN) and titanium nitride with silver nanoparticles (TiN/Ag). Antibacterial activity was tested against common biofilm-forming pathogens, including Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. The results demonstrated that both coatings significantly reduced bacterial cell counts, with the TiN/Ag coating showing superior performance due to the addition of silver nanoparticles. This enhancement was particularly effective in reducing biofilm formation across all the tested strains, with the most pronounced effects observed for E. faecium and E. faecalis. The silver nanoparticles synergistically improved the antibiofilm properties of the TiN coating, efficiently disrupting biofilm integrity and reducing bacterial adhesion. By reducing bacterial attachment and biofilm formation on biomaterial surfaces, TiN/Ag coatings offer a promising strategy to minimize complications associated with biomaterial implants. These findings highlight the potential of TiN and TiN/Ag coatings for medical applications.