Antibiotic resistance is currently a global problem for modern civilization. Microorganisms become resistant to drugs through acquired mechanisms. Six pathogens are responsible for the majority of deaths: Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa. Growing drug resistance makes basic antibiotic therapy ineffective and increases the costs of polytherapy [1]. In recent years, there has been increasing interest in organic compounds that contain an aryl or a heteroarylsulfonamide group in their structure, which are characterized not only by anticancer activity but also by antimicrobial activity [2]. The presented studies follow the trend of searching for new hybrid molecules resulting from the combination of different pharmacophores with interesting biological profiles.

The antibacterial activity of compounds that had previously shown interesting anticancer activity was assessed [3]. The compounds were subjected to an assessment of their antibacterial activity in in vitro tests against the Gram-positive bacterium Staphylococcus aureus (MIC = 8 µg/mL) and the Gram-negative Escherichia coli (MIC > 125 µg/mL). The most active derivative (16) was tested against the Gram-positive bacteria S. epimermidis, E. faecalis, and B. subtilis (MICs in a range from 2 to 125 µg/mL) and clinical strains of MRSA (MICs between 0.5 and 1 µg/mL). Ampicillin was used as the standard. The activity of the tested compound against a bacterial biofilm was also tested, and its hemolytic activity was assessed in the peripheral blood of domestic sheep.

References:

[1] Uddin T. M., Chakraborty A. J., Khusro A., Zidan R. M., Mitra S., Emran T. B., Dhama K., Ripon K. H., Gajdács M., Sahibzada M. U. K., Hossain J.; J. Infect. Public Health (2021), 14 (12), 1750.

[2] Verma S. K., Verma R., Xue F., Thakur P. K., Girish Y. R., Rakesh K. P.; Bioorg. Chem. (2020), 105, 104400.

[3] Bułakowska A., Sławiński J., Siedlecka-Kroplewska K., Stasiłojć G., Serocki M., Heldt M., Bioorg. Chem. (2020), 104, 10430.

The growing resistance to antimicrobial drugs has significantly complicated the effective treatment of infections, prompting global efforts to address this crisis. The World Health Organization (WHO) has prioritized pathogenic bacteria in a recent report to guide research and public health initiatives. This report underscores the critical role of biofilm-associated infections and highlights the need for innovative strategies to combat multidrug-resistant microorganisms. Among such strategies, the green synthesis of metallic nanoparticles has emerged as a promising approach. This environmentally friendly method yields biocompatible materials with significant biomedical potential. Biogenic zinc nanoparticles (ZnNPs), synthesized via eco-friendly methods using Pseudomonas aeruginosa, offer a promising approach for biofilm eradication and combating microbial resistance. This study evaluates the antibacterial and antibiofilm activities of biogenic ZnNPs against clinically relevant microorganisms, including biofilm-forming bacterial strains such as Staphylococcus aureus and Escherichia coli.

Antimicrobial effects were assessed using broth microdilution and time-kill assays. Biofilm formation and eradication were evaluated through crystal violet staining, resazurin assays, and colony-forming unit quantification. Additionally, the oxidative and nitrosative stress toxicity mechanisms triggered by ZnNPs, particularly those related to cellular stress, were investigated. The results demonstrated that ZnNPs exhibit concentration-dependent inhibitory effects on both prokaryotic microorganisms. ZnNPs inhibited biofilm formation by up to 50% in E. coli and yeast species and up to 80% in S. aureus. These antibiofilm activities were attributed to disruptions in cellular stress metabolism, primarily driven by nitrosative stress through enhanced production of reactive nitrogen intermediates.

The findings reveal significant antimicrobial activity, effectively targeting bacterial biofilms. These results demonstrate the potential of ZnNPs as an innovative strategy for managing biofilm-related complications. Furthermore, they underscore the importance of developing sustainable approaches to address the growing challenge of antimicrobial resistance, providing a strong foundation for future advancements in antimicrobial therapies.

Antibiotic resistance has become one of the biggest threats to modern medicine. The World Health Organization (WHO) and other health organizations warn that if antibiotic resistance is not brought under control, even simple infections can become deadly. The overuse and misuse of antibiotics lead to the emergence of resistant bacterial strains, creating a major challenge, especially in the treatment of foodborne pathogens. In response to this growing crisis, researchers are increasingly turning to natural antimicrobial alternatives. Consumer demand for organic and sustainable products has increased interest in the use of plant-derived bioactive compounds as natural preservatives.Camellia japonica flowers contain bioactive molecules such as phenolic compounds, anthocyanins, and polyphenols and may exhibit antimicrobial properties. In this study, the antimicrobial activity of C. japonica flowers (var. Dr Tinsley) against foodborne pathogens was evaluated using the agar diffusion method. The extracts were obtained by a conventional maceration technique (50 °C, 1 h) using 60% methanol solvent and were then lyophilized and re-suspended in dimethyl sulfoxide (DMSO). The results revealed that C. japonica (var. Dr Tinsley) extract showed significant antimicrobial activity against Staphylococcus epidermidis (11.24 mm), Staphylococcus aureus (10.98 mm), Pseudomonas aeruginosa (10.03 mm), Salmonella enteritidis (6.30 mm), and Bacillus cereus (6.54 mm). However, no inhibition was observed against Escherichia coli. A total of 15 μL of 40% lactic acid was used as a positive control, producing inhibition zones of 17.53 mm for E. coli, 16.4 mm for S. aureus, 18.41 mm for S. enteritidis, 12.53 mm for P. aeruginosa, and 14.76 mm for B. cereus. Meanwhile, 15 μL of DMSO served as the negative control, showing no inhibition. These findings suggest that C. japonica (var. Dr Tinsley) flowers have the potential to be used as bioprotectants in the food and pharmaceutical industries. Further research is needed to isolate and characterize the active compounds responsible for these effects.

Introduction: Medicinal plants are a great source of bioactive compounds, such as secondary metabolites, with diverse biological activities, including antibacterial properties. The rise of antibiotic-resistant bacteria poses a significant threat to public health, necessitating the search for novel antibacterial agents. This research explored the presence of secondary metabolites such as flavonoids, tannins, saponins, and carotenoids, followed by the identification of CHS, SQS, PSY, and LAR genes and the antibacterial potential of medicinal plants such as Aloe barbadensis and Mentha piperita. The aim was to identify promising candidates for further investigation and development of antibacterial therapies.

Methods: This study was conducted using triplicates of Aloe barbadensis and Mentha piperita leaves. Both ethanolic and methanolic crude extracts of these plants were used. The methanolic and ethanolic crude extracts of the selected plants were used, as both have good solubility. The antibacterial profiling was also conducted using agar well diffusion, and the Minimum Inhibitory Concentrations (MICs) against four bacterial strains (Klebsiella pneumoniae, Escherichia fergusonii Enterobacter cloacae & Citrobacter amalonaticus) were established. The presence of CHS, SQS, PSY, and LAR genes was investigated using Polymerase Chain Reaction (PCR) of secondary metabolites.

Results: Both extracts showed almost consistent phenotypic results. None of the samples contained all four screened classes of secondary metabolites. The methanolic extracts showed higher antibacterial activity than the ethanolic extracts. Mint leaf was found to have a higher antibacterial potency compared to aloe vera. On the other hand, aloe vera showed positive results in the genotypic analysis, containing all four secondary metabolites. The mint did not contain any of the targeted genes in this study.

Conclusion: According to this study, the findings of the two samples were not aligned with the phenotypic and genotypic results. However, both samples were found to be a potential target in different analyses, suggesting their therapeutic potential. Further research can be conducted using larger number of samples to explore the underlying mechanisms.

Antimicrobial resistance (AMR) is no longer a future threat but a latent reality that accounts for more than 1 million deaths annually, based on recent data from the World Health Organization (WHO). This jeopardizes the effectiveness of healthcare treatments and poses a potential risk to global public health. The spread of AMR is related to factors such as the overuse of antibiotics and its global spread. Given the urgent need for natural antimicrobial alternatives with mechanisms of action different from conventional antibiotics, plant-derived compounds have emerged as promising candidates. Camellia japonica L. is a perennial shrub belonging to the Theaceae family, which has become popular for its garish flowers and the landscaping they provide. The species is native to East Asia and has been traditionally used both in the horticultural industry and for its medicinal properties. Although seed oil is known for its cosmetic and culinary uses as a preservative, the leaves have not been widely studied for their antimicrobial activity. In this work, the natural antibacterial activity of the leaves of C. japonica L., obtained by a simple and economical extraction method such as maceration, has been evaluated against food-borne pathogens in microbiological media. The screened exhibited antimicrobial activity with inhibition zones of 11.87 mm against Pseudomonas aeruginosa and 11.73 mm against Salmonella enteritidis compared to 12.53 mm and 18.41 mm for the positive control, lactic acid, respectively. However, against Escherichia coli, Staphylococcus aureus, and Bacillus cereus, the leaves of C. japonica did not show any activity. These results suggest that C. japonica leaves have selective antimicrobial potential, particularly against P. aeruginosa and S. enteritidis. Further research needs to be carried out to identify and explore their potential applications.

Introduction: Oral polymicrobial biofilm formation occurs as a result of the synergistic interaction of fungal (e.g., Candida albicans) and bacterial pathogens (e.g., Staphylococcus aureus) and has been reported to cause severe dental caries and periodontal diseases. One of the promising ways of combating biofilms is the use of nanoparticles (NPs) manufactured utilizing green chemistry. The present study aimed to synthesize gold NPs using fucoidan, β-caryophyllene, and phloroglucinol to control oral polymicrobial biofilms caused by S. aureus and C. albicans.

Methods: Fucoidan–gold nanoparticles (Fu-AuNPs), β-caryophyllene–gold nanoparticles (β-c-AuNPs), and phloroglucinol–gold nanoparticles (PG-AuNPs) were synthesized using natural molecules. These NPs were characterized using UV-vis absorption spectroscopy, FTIR, FE-TEM, EDS, DLS, zeta potential, and XRD. The colony counting method was employed to check the antibiofilm effects of these NPs towards polymicrobial biofilms of S. aureus and C. albicans.

Results: The synthesized Fu-AuNPs, β-c-AuNPs, and PG-AuNPs were found to be spherical in morphology, with sizes of 75.66 ± 9.28 nm, 17.6 ± 1.2 nm, and 46.71 ± 6.40 nm, respectively. The minimal inhibitory concentration (MIC) of Fu-AuNPs, β-c-AuNPs, and PG-AuNPs against S. aureus and C. albicans was determined to be 1024 μg/mL, 512 μg/mL, and 2048 μg/mL, respectively. The inhibition of polymicrobial biofilms of S. aureus and C. albicans by these NPs was significant at the sub-MIC level and was concentration-dependent. In addition, Fu-AuNPs, β-c-AuNPs, and PG-AuNPs at MIC and above MIC significantly eradicated mature polymicrobial biofilm.

Conclusions: This study demonstrated that Fu-AuNPs, β-c-AuNPs, and PG-AuNPs act as an alternative strategy to control oral pathogens by inhibiting the initial stage of biofilm formation and eradicating mature polymicrobial biofilms of S. aureus and C. albicans.

Funding: This research was supported by the Basic Science Research Program through a National Research Foundation of Korea grant funded by the Ministry of Education (RS-2023-00241461) and Research Grant of Pukyong National University in 2024 (202416570001).

The opportunistic pathogen Pseudomonas aeruginosa causes nosocomial infections affecting the urinary system, respiratory tract, etc. It can lead to bacteremia and sepsis, especially in immunocompromised patients. Growing antimicrobial resistance (AMR) is a global health concern according to the World Health Organization. Therefore, novel antimicrobial agents, such as plant extracts containing complexes of compounds to which it is impossible to develop resistance, are being investigated. This study aimed to compare the effects of ethyl acetate (EtOAc) extracts from the roots (EtOAcR) and aerial parts (EtOAcAP) of the perennial Bulgarian plant Geum urbanum L. (Rosacea) on the phenotype inhibition of the Las/RhI quorum sensing (QS) system in Pseudomonas aeruginosa PA01 and ATCC 27853, specifically on biofilm formation, swarming motility, pyocyanin production, and gene expression. For this purpose, we used sub-minimal inhibition concentrations (sub-MICs), which do not affect bacterial growth. We found that the evaluated sub-MICs suppressed all studied phenotypic manifestations, with no expression of the target lasI/lasR and rhII/rhIR genes. The observed anti-QS capacity of G. urbanum extracts is probably related to their high phenolic content. Moreover, the EtOAcR and EtOAcAP extracts showed effective antioxidant capacity via DPPH, ABTS, and superoxide radical scavenging effects, as well copper ion chelation activity. These findings will support the development of novel phytocomplexes applicable for the biocontrol and prevention of P. aeruginosa infections.

Lichens are symbiotic organisms resulting from the mutualistic interaction between a fungus, an alga, and/or a cyanobacterium, along with an associated microbiome, which has enabled their adaptation to various ecosystems across the planet. Throughout this process, they have developed secondary metabolites with a broad spectrum of biological activities. This study explores the potential of bioactive compounds found in Antarctic lichens as antimicrobial agents. Ethanol extracts from species belonging to the genera Cladonia, Gondwania, Himantormia, Lecania, Ochrolechia, Placopsis, Pseudephebe, Psoroma, Sphaerophorus, and Umbilicaria have revealed aromatic compounds from the depside, depsidone, and dibenzofuran groups with variable and significant ranges of antioxidant activity (DPPH IC₅₀ 75.3 ± 0.02 - 2246.149 ± 0.086 µg/mL; ORAC 18.882 ± 0.210 – 525.11 ± 0.135 µmol Trolox/g) and enzymatic inhibition (acetylcholinesterase IC₅₀ 2.805 ± 0.07 – 32.880 ± 0.016 µg/mL; butyrylcholinesterase IC₅₀ 4.476 ± 0.06 – 57.925 ± 0.030 µg/mL; α-glucosidase IC₅₀ 16 ± 0.015 – 250.443 ± 0.006 µg/mL; tyrosinase IC₅₀ 22.32 ± 0.21 - 68.436 ± 0.048 µg/mL), suggesting their potential for antimicrobial research. Additionally, various studies have demonstrated the antimicrobial activity of extracts and isolated compounds from lichens such as Cetraria aculeata, Cladonia rangiferina, Parmelia sulcata, Parmotrema dilatatum, Stereocaulon alpinum, and Usnea barbata against pathogenic bacteria including Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Salmonella enterica, Klebsiella pneumoniae, Enterococcus faecalis, Listeria monocytogenes, and Streptococcus pneumonia, with minimum inhibitory concentrations (MICs) varying between 0.2 and 8.5 mg/mL. The identified mechanisms of action include the inhibition of nucleic acid and protein synthesis, the disruption of cellular integrity, enzymatic activity inhibition, oxidative stress induction, and biofilm formation inhibition. The compounds present in Antarctic lichens represent a promising and innovative therapeutic alternative for combating bacterial infections. However, further in vitro and in vivo studies are essential to validate their safety and efficacy within the context of increasing antimicrobial resistance.

Klebsiella pneumoniae is an opportunistic pathogen that can acquire multiple antimicrobial resistance mechanisms. The presence of multidrug-resistant K. pneumoniae in food-producing animals raises concerns about its potential role in the dissemination of resistance genes. This study aimed to investigate the occurrence of K. pneumoniae in healthy meat rabbits and characterize its antimicrobial resistance and virulence profiles.

A total of 295 fecal samples were collected from 20 rabbit farms in northern Portugal. Samples were incubated in BHI broth and plated on Chromocult Coliform Agar with cefotaxime (2 µg/mL). Pink colonies were subcultured on BHI agar and identified by MALDI-TOF MS. Antimicrobial susceptibility was assessed by the Kirby–Bauer method, and whole-genome sequencing was performed to detect resistance and virulence genes, as well as clonal lineages.

Out of the 295 samples, only 6 (2%) ESBL-producing K. pneumoniae were isolated. All isolates were multidrug-resistant, as they were resistant to at least three classes of antibiotics. All isolates carried ESBL-related genes, including bla_TEM-1(5/6), bla_CTX-M-15 (2/6), and bla_SHV variants (bla_SHV-1, bla_SHV-28, bla_SHV-38, bla_SHV-61), as well as bla_OXA-1 in two isolates. Genes associated with aminoglycoside resistance were identified in all isolates, such as aph(3'')-Ib, aph(6)-Id, and aac(3)-IIe/IVa. Tetracycline resistance was mainly mediated by tet(A) and tet(D), while sulfonamide resistance was conferred by sul1 and sul2. Among fluoroquinolone resistance genes, qnrB1 and qnrS1 were detected. The fosA gene, conferring resistance to fosfomycin, was also present. Genes associated with heavy-metal resistance (sil and pco) were found in all isolates. All isolates carried regulators such as ramA, marA, and baeR, which modulate efflux pump. Isolates were ascribed to ST307, ST45, ST193, and ST2026.

These findings reinforce the need for the continuous monitoring of antimicrobial resistance in K. pneumoniae from food-producing animals, as their potential role in the spread of resistance genes poses a risk to public health.

Campylobacter spp. is one of the leading causes of foodborne bacterial gastrointestinal illnesses in humans, primarily through chicken meat. The prevalence of antibiotic-resistant Campylobacter strains in chicken is increasing worldwide. This fact makes it necessary to evaluate antimicrobial effectiveness, particularly through in vivo models such as Galleria mellonella larvae (GML). In this work, GML were infected with strains of C. coli and treated with tetracycline (8, 12, 15, 20, and 40 mg/mL); after that, all groups were cultivated at 37°C for 4 days without feeding. In this period, mortality, bacterial load in hemolymph, and hemocyte count were assessed. The results showed that the group treated with 8 and 12 mg/mL of tetracycline had its mortality reduced to less than 10% in the first 3 days. In contrast, higher doses (15, 20, and 40 mg/ml) showed no significant difference compared to the infected group without antibiotic treatment. Bacterial load decreased by more than 3 log₁₀ in the first 0.5 hours in the treated groups. No difference was observed in the number of hemocytes between treated and untreated larvae. Treatment with tetracycline at 12 mg/ml was the most effective in reducing larval mortality and controlling C. coli infection. These results suggest the usefulness of the Galleria mellonella larvae model in evaluating antibiotic dosages against C.coli.