Antimicrobial Activity of Ten Local Actinobacterial Strains against ESKAPE, Bacillus subtilis and Pseudomonas baetica Pathogens

Aims: The study included the isolation, purification, cultural characteristics, antimicrobial activities and molecular identification of local actinobacterial strains isolated from different locations north of Iraq.

Methodology: Oligotrophic medium supplemented with the antifungals cycloheximide (50 mg/l) and nystatin (30 mg/l) was used for preliminary isolation. ISP-3 medium was chosen as a potential medium for subsequent purification of actinobacterial strains. The cultural characteristics of all isolated actinobacterial strains were elucidated on International Streptomyces Project media (ISP2-ISP-7). 16S rRNA marker gene was used for molecular identification using 27F and 1492R universal primers.

Results: Ten isolates were biologically active against tested ESKAPE, Bacillus subtilis and pseudomonas paetica pathogens when cultured on different ISPs media under the OSMAC approach. Six representative isolates that exhibited antimicrobial activity against all or almost tested bacteria were sequenced using 16S rRNA gene. The sequences were compared with those of other actinobacterial strains that are found in Genebank database to find the best similarity and the close reference strains to our isolates. Five of the sequenced strains have been identified as Streptomyces species; MT5, MT8, MT12, MT23 and MT26 and one was identified as a rare actinobacterial strain Lentzea sp.; MT4. Nucleotide sequences have been provided and deposited in the National Center for Biotechnology Information NCBI under the accession numbers ON514131, ON514133, ON514134, ON514135, ON514136 and ON514130 respectively.