Isolation and Antibacterial Properties of Actinomycetes From Yellow Olive Tree (Olea europaea)

The symbiotic relationships between actinomycetes and their host plants further enhance their potential as sources of bioactive compounds. These bacteria produce a wide array of secondary metabolites with antimicrobial, insecticidal, and anticancer properties, making them valuable for bioprospecting in pharmaceuticals and agriculture. The ineffectiveness of existing antibiotics has resulted in higher morbidity and mortality rates, alongside escalating healthcare costs due to treatment failures. The rise of multidrug-resistant (MDR) pathogens poses a significant threat to global health, necessitating the discovery of novel antimicrobial agents.

This study isolates and characterizes endophytic actinomycetes from the yellow olive tree (Olea europaea), a plant known for its rich phytochemical composition, to evaluate their antibacterial potential against ESKAPE pathogens. Samples were collected from olive tree roots, yielding 54 bacterial isolates, of which 45(83.3%) were identified as actinomycetes through 16S rRNA gene amplification. Among these, 16 isolates (35.6%) exhibited antibacterial activity against drug-sensitive and drug-resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae.

Molecular screening revealed that 66.7%, 28.9%, and 93.3% of the isolates harbored non-ribosomal peptide synthetase (NRPS), polyketide synthase I (PKS-I), and polyketide synthase II (PKS-II) genes, respectively, which are associated with secondary metabolites biosynthesis. However, no direct correlation was found between these biosynthetic genes and antibacterial activity, suggesting that gene expression and environmental factors play crucial roles in metabolite production.

The study highlights the potential of endophytic actinomycetes from O. europaea as a source of novel antimicrobial compounds, particularly in the fight against MDR pathogens. These findings underscore the importance of exploring plant-associated microbes for developing new therapeutic agents to address the global antibiotic resistance crisis.