Resazurin based rapid screening and Spectrophotometric analysis of potent antimicrobials from Streptomyces isolated in Nepal

Background: The rapid emergence of bacterial resistance and decreased efficacy of most antibiotics is a burning issue in the present medical world demanding swift development of novel classes of potent antibiotics. This study focuses on the robust assay of screening antimicrobials speeding up the antibiotics discovery process. Results Putative Streptomyces designated as LAf4 isolated from a soil sample of Lamjung, mid-hills of Nepal, screened from 141 putative Streptomyces isolates had the highest inhibitory effect among all the strains that showed inhibition potential against two of the ‘critical’ WHO prioritized pathogens including Klebsiella pneumoniae and Pseudomonas aeruginosa,. The results from Resazurin based assays were all verified using broth assays for antimicrobial studies. The proposed method was efficient, easy to observe and gave results a lot faster than the conventional antimicrobial study. Also, a novel spectrophotometric analysis method has been proposed to access the potency of thus screened antimicrobials. GCMS analysis of LAf4 extract indicated the presence of 2,3-butanediol, Naphthalene, and Tributyl phosphate as major constituents exhibiting antimicrobial properties whereas Pyrrolo (1, 2- a) pyrazine -1,4-dione, hexahydro-3-(2-methylpropyl)- which is an antioxidant and an anticancer agent was also recorded.Conclusion The present study validates and exhibits the time and cost effective resazurin based antimicrobial assay as the best one, for preliminary screening of antimicrobial producers compared to conventional disc/well diffusion assays since very small concentration of antimicrobials irrespective of their polarity can be detected unlike the latter methods.