COMPARATIVE POTENTIAL OF ENDOPHYTIC EXTRACTS AS NATURAL ALTERNATIVES TO ANTIBACTERIAL DRUGS

SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 113 COMPARATIVE POTENTIAL OF ENDOPHYTIC EXTRACTS AS NATURAL ALTERNATIVES TO ANTIBACTERIAL DRUGS B.B. Tojiyev1, U.K. Yusupov2, D.M. Ruziyeva3 PhD student, Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan1 Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan2 PhD in Biological Sciences, Senior Researcher, Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan3 https://doi.org/10.5281/zenodo.17674479 Abstract. The aim of this study was to compare the antibacterial activity of the endophytic extract of the Alternaria 8S sp. strain isolated from Ginkgo biloba L. and the AV4L isolate obtained from Aloe vera. The assays demonstrated that the Alternaria 8S sp. strain exhibits a more pronounced bactericidal effect against test cultures such as Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, and Candida albicans compared to AV4L, which showed moderate bactericidal activity. Differences in the degree of antibacterial effect were observed based on preliminary results, while the composition of active compounds and their mechanisms of action require further investigation. The obtained findings support the potential of endophytic fungi as promising sources of natural antibacterial agents. Keywords: alternaria 8S sp., Aloe vera, AV4L, antibacterial activity, endophytes. Introduction It has been noticed recently that the number of pathogenic microorganisms resistant to already existing antibiotics has noticeably increased. This fact is considered to be a serious threat to human health and requires the urgent search for new sources of antimicrobial compounds. One of the most promising trends in modern microbiology and biotechnology is the research of natural compounds synthesized by microorganisms and plants that have demonstrated pronounced antibacterial activity. Of particular interest is a group of endophytic microorganisms, which includes bacteria and fungi that live in plant tissues without causing pathological changes. Plant metabolites still represent the most significant source of discovery of new and potentially valuable pharmaceuticals. However, extraction from plant sources is limited due to season ability, the influence of climatic conditions, and the need for cultivation areas. An alternative source that is highly promising, inexhaustible, and renewable for high-value bioactive products is endophytic fungi, that asymptomatically inhabit various parts of all existing plant species [1]. These microorganisms are capable of synthesizing a wide variety of secondary metabolites similar in their activity to plant-derived compounds, often more stable and effective. Special mention should be given to representatives of the genus Alternaria, which have been reported to exhibit antagonistic activity against various pathogenic bacteria and fungi. On the other hand, Aloe vera AV4L continues to be one of the most studied medicinal plant, the extracts of which serve as natural antiseptics and sources of biologically active substances. However, few studies have been conducted on the comparative antibacterial action of endophytic fungi and plant extracts especially under conditions of local isolation and testing [2]. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 114 In this respect, the goal of the current study was to perform a comparative analysis of the antibacterial action of the Alternaria 8S sp. strain and the endophytic extract AV4L from Aloe vera against multiple pathogenic microorganisms. Materials and methods Extraction of Secondary Metabolites from Endophytic Fungi. To determine biological activity, the extraction of secondary metabolites from the biomass of endophytic fungi was carried out according to methodologies described in several international scientific studies, with laboratory modifications introduced as needed [3]. Approximately 5 g of frozen fungal biomass were thoroughly ground in a mortar with sterile glass sand, after which 50 mL of ethyl acetate (EtOAc) was added as the extraction solvent. The resulting suspension was transferred into a conical flask and incubated on a shaker at room temperature for 24 hours. The mixture was then filtered through Whatman №1 filter paper, and anhydrous sodium sulfate (Na₂SO₄) was added to remove residual moisture. Subsequently, the filtrate was evaporated to dryness using a rotary evaporator under reduced pressure [4]. The remaining residue was dissolved in 1 mL of dimethyl sulfoxide (DMSO) to obtain a stock extract, which was stored at +4 °C until further use. The obtained extracts were used to assess antibacterial and antifungal activities [5]. The antibacterial properties of the extracts were determined using the well-diffusion method against the following test cultures: gram-positive bacteria (S. aureus and B. subtilis), gramnegative bacteria (E. coli and P. aeruginosa), as well as yeast (C. albicans). Meat-peptone agar (HiMedia, India) was used for testing the extracts. Petri dishes containing the nutrient medium were inoculated with a 24-hour suspension of the test cultures prepared in physiological saline at a concentration of 1.5 × 10⁸ CFU/mL, corresponding to the McFarland standard. After slight drying, wells with a diameter of 5 mm were cut into the agar, and 100 μL of each extract was added into the wells in triplicate. The plates were incubated at 37 °C for 24–48 hours. Ceftriaxone (a third-generation cephalosporin antibiotic, 30 μg/disc) served as the positive control, while dimethyl sulfoxide (DMSO), the solvent for the secondary metabolite extracts of endophytic fungi, was used as the negative control. The results were evaluated by measuring the diameters (in millimeters) of the inhibition zones formed around the wells [1]. Results and discussion The antibacterial activity of the biomass extracts of Alternaria 8S sp. and AV4L was evaluated using the agar diffusion method against five test cultures: Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, and Candida albicans (Table 1). Sample S. aureus P. aeruginosa B. subtilis E. coli C. albicans Alternaria 8S sp. 29 mm 24 mm 28 mm 35 mm 21 mm AV4L 16 mm 20 mm 13 mm 16 mm 16 mm Table 1. Antibacterial activity of Alternaria 8S sp. and AV4L extracts against selected test microorganisms. The obtained data on the antibacterial activity of the Alternaria 8S sp. and AV4L extracts clearly demonstrate a distinct advantage of the fungal isolate over the plant-derived extract. The Alternaria 8S sp. extract exhibited pronounced inhibitory activity against all five test cultures, including both gram-positive (S. aureus, B. subtilis) and gram-negative (E. coli, P. aeruginosa) bacteria, as well as C. albicans. The maximum inhibition zones (35 mm for E. coli and 29 mm for S. aureus) are comparable to, or even exceed, the values reported in several published studies. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 115 With regard to plant-derived extracts of Ginkgo biloba, data from several studies indicate that they also demonstrate antimicrobial activity against both gram-positive and gram-negative microorganisms. However, the inhibition zones typically range from 12 to 25 mm, making the antimicrobial activity of Ginkgo biloba comparable to that of AV4L. In contrast, the Alternaria 8S sp. isolate exhibits a significantly stronger antagonistic effect, highlighting its potential value as a source of biologically active compounds [6-7]. Conclusion Overall, these findings indicate that Alternaria 8S sp. demonstrates antibacterial activity that is comparable to or surpasses the activity of Ginkgo biloba and Aloe vera extracts reported in the literature. While plant extracts such as Aloe and Ginkgo traditionally contain a wide spectrum of phenolic compounds with moderate antimicrobial effects, endophytic fungi are capable of synthesizing more specific and potent secondary metabolites—such as alternariol, alternariol monomethyl ether, tenuazonic acid, and other derivatives—which possess strong bactericidal properties. This likely explains the superior activity of Alternaria 8S sp. compared to AV4L and the plant-derived extracts described in previous studies. 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