Bioprospecting actinobacterial diversity antagonistic to multidrug-resistant bacteria from untapped soil resources of Kotdiji, Pakistan

Untapped environments have been considered as potential resources of novel actinobacteria to combat multidrug resistance. The present study relates with isolation and characterization of potential antibiotic-producing soil actinobacterial diversity of district Khairpur Mir's, Pakistan. The soil actinobacteria from eighteen different soil samples were isolated on starch casein agar and preliminarily identified based on morpho-microscopic and biochemical characteristics. Four in vitro screening approaches viz. cross streak method and lawn method (primary screening) and agar-well diffusion and disc-diffusion method (secondary screening) were used to test antimicrobial potential of the isolated actinobacteria. The panel of test bacterial strains consisted of six multidrug-resistant (MDR) bacterial pathogens of clinical origin including; Staphylococcus aureus, Staphylococcus haemolyticus, Escherichia coli, Salmonella typhi, Enterobacter spp. and Pseudomonas aeruginosa. Total twenty-six (26) different actinobacterial strains were isolated and characterized. Moreover, 11/26(42.3%) actinobacteria isolates displayed broad-spectrum antagonistic activity against all the test bacterial strains. Based on significant antagonistic activity, the isolate B3d was selected and further identified using 16S rRNA genotyping as Streptomyces thermolilacinus. To the best of our knowledge, this is the first report on any S. thermolilacinus strain exhibiting significant broad-spectrum antagonistic activities against MDR pathogens that could serve as candidate for novel drug discovery. Therefore, exploration of more untapped resources is strongly needed for isolating novel actinobacterial species capable of biosynthesizing novel drug leads to combat MDR bacteria.