Isolation and Discovery of New Antimicrobial-agent Producer Strains Using Antibacterial Screening of Halophilic Gram-positive Endospore-forming Bacteria Isolated from Saline Lakes of Iran

Abstract Background: Today, discovery and production of new antimicrobial drugs has been emphasized due to the growing of antimicrobial resistance. The purpose of this study was to screen out antimicrobial producing bacteria among halophilic or halotolerant Gram-positive endospore-forming bacteria isolated from different areas of Iran. Materials and Methods: 62 strains were isolated from salin lakes of Iran, endospore-forming ability was evaluated and further identification of strains was done using 16S rRNA gene sequencing. Screening test was performed using two-layer agar diffusion method in which the indicator strains, Bacillus cereus (ATCC 14579) and Escherichia coli, (PTCC 1330) were inoculated in the seed layer. Finally, the production of antimicrobial active agent during a period of 7 days was studied followed by evaluating the effect of base-layer agar concentration on the dissemination of antibacterial metabolite. Results: Isolates WT6, R4A19 produced an agent(s) which inhibited the growth of both B.cereuse and E.Coli. The inhibition zone against only E.Coli was observed when R4A20 strain had been cultured in the base layer, while four non-bacillus strains (R4S2, LbS2, RF1 and WT19) could inhibit the growth of B.cereuse. The antibacterial compound production of WT6 against Bacillus cereuse and E.Coli reached to its optimumm leved after 3 and 4 days respectively, while R4A20 produced the active substance, optimally, after 5 days. No significant difference effect on diameter of zone inhibition was observed among various base-layer agar concentrations. Conclusion: Halophile or halotolerant endospore-forming bacteria isolated from different areas of Iran possess a potential to be considered as interesting microorganisms for further antimicrobial research studies