Antimicrobial Activities of the Secondary Metabolite Extracted from a Nocardia Strain

Background & Objective: The emergence of antibiotic-resistant bacteria and limited treatment options for these infections is a challenging problem in the world. There is increasing interest in isolating bioactive molecules from actinobacteria and elucidating their antimicrobial mechanisms at the moment. The current study aimed to investigate the antimicrobial activities of a Nocardia strain (N۴) that was previously isolated from the soil samples in Tehran, Iran.  Materials & Methods: The cultural, morphological, and physiological characteristics of the strain were determined and the identity of the strain was confirmed using ۱۶SrRNA gene sequencing. The strain was screened for antimicrobial metabolite production. The in vitro anti-microbial activity of the extracted metabolite was assessed by agar well diffusion and minimum inhibitory concentrations methods. Finally, the structure of the extracted metabolite was confirmed by HPLC and mass spectrometry methods. Results: The isolate shared ۹۹% sequence similarity with Nocardia soli. The strain showed broad-spectrum antimicrobial activities against some pathogenic bacteria (Escherichia coli ATCC ۲۵۹۲۲, Pseudomonas aeruginosa ATCC ۲۷۸۵۳, Klebsiella pneumoniae ATCC ۷۰۰۶۰۳, Salmonella Typhimurium ATCC ۱۴۰۲۸ and Shigella sonnei RI۳۶۶) and fungi (Aspergillus niger ATCC ۱۰۱۵ and Aspergillus fumigatus ATCC ۱۰۲۲) in the agar well diffusion method. The ethyl acetate extract of the strain exhibited the highest antimicrobial activity against E. coli (MIC= ۴.۶۷±۳.۰۵۵ μg/mL) and K. pneumoniae (MIC=۳.۳۳±۱.۱۵۵ μg/mL). The metabolite showed high similarity with C۲۱H۲۸N۷O۱۴. Conclusions: The current study confirmed the presence of a bioactive metabolite in strain N۴, suggesting that this may be a promising candidate for discovering bioactive components with broad antibacterial activities against a variety of pathogens Keywords:

Keywords:

Nocardia soli , antimicrobial activity , HPLC , Bioactive Metabolite