Seyedeh Shaghayegh Hoseini - Department of Microbiology, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran
Atousa Ferdousi - Department of Microbiology, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran
Mansoureh Paknejadi - Department of Microbiology, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran

Background and Objective: Today, the importance of different ecosystems for discovering biotechnologicalresources has become more and more apparent to researchers. One of the major challenges is theoccurrence of antibiotic resistance in pathogenic microorganisms and the increased rate of mortality dueto infections caused by them worldwide. Researchers believe that an appropriate solution to overcomethis challenge is trying to find effective alternatives to the current antibiotics. To the best of this researchteam's knowledge, the water and soil ecosystem of Chitgar Forest Park has not been searched for thepresence of antimicrobial-producing microorganisms. The aim of this study is to investigate thisecological niche in terms of the potential presence of antibiotic-producing bacteria.Methods: In this study, ۱۲ samples of water and ۱۲ of soil around the plant’s roots were collected andtransferred to the laboratory. After primary screening with the Streak Cross method, isolates with greaterability to produce antibiotics were selected, and then, their extracts were provided, using the SubmergedFermentation technique. In the secondary screening by Agar well diffusion method, the antimicrobialeffect of the extracts on the five human pathogens was investigated. Finally, DNA extraction andmolecular sequencing were carried out along with drawing a phylogenetic tree for the isolates that had thehighest effectiveness against test pathogens.Results: During the primary and secondary screening, the top ۳ samples were isolated from the soil. Twoisolates had the most antimicrobial properties against the test pathogens include: Klebsiella oxytoca,Proteus vulgaris, Streptococcus mutans, Proteus mirabilis, and Shigella boydii. The results show that thediameter of inhibition zone was in the range of ۱۱ to ۱۵ mm, which is more effective compared to thecontrol discs (penicillin ۱۰ mm and erythromycin ۱۲ mm) and ethyl acetate control (no significant theinhibition zone). Based on the sequencing results and related phylogenetic tree, two selected sampleswere identified as Bacillus licheniiformis with accession number MT۳۲۶۲۳۳.۱ and Bacillus cereus strainDBA۱.۱ with accession number MT۳۳۲۱۵۶.۱.Conclusion: In the present research, like many other studies, strains of the genus Bacillus were reportedas the most abundant and best producers of antibiotics. Also, the results show that the Chitgar Forest Parkecosystem has diverse biological resources of microorganisms that produce antimicrobial substanceswhich can be used as a suitable alternative to common antibiotics against drug-resistant pathogens. Inaddition, it is suggested that this ecosystem be further investigated to find other microorganisms withbiotechnological applications.

Antimicrobial agents, Natural ecosystem, Phylogenetic tree, Screening