Inhibition of growth and biofilm formation of some multidrug-resistant bacteria by Streptomyces secondary metabolites

ObjectiveThis study set out to explore the antimicrobial potential of actinobacteria collected from the rhizosphere soil of date palms, with particular attention to their ability to suppress the growth and biofilm formation of common bacterial pathogens. MethodsFifteen actinobacterial strains were isolated from soil samples taken in Jeddah and Al-Madina Al-Monawara. The isolates were cultured on starch nitrate medium containing 5 mg/mL of nystatin to reduce fungal contamination. ResultsOf the 15 isolates, three showed clear antibacterial activity against Escherichia coli, Staphylococcus aureus, MRSA, Staphylococcus saprophyticus, Salmonella typhi, and Klebsiella pneumoniae. Inhibition was confirmed using both cross-streak and agar well diffusion techniques, with zones ranging from 12.5 to 25 mm, particularly against MRSA, S. typhi, K. pneumoniae, and S. saprophyticus. Detailed morphological, cultural, physiological, and biochemical tests were carried out, followed by 16S rRNA gene sequencing. The active isolates were identified as members of the genus Streptomyces: S. yangpuensis (PV639342), S. vinaceusdrappus (PV639359), and S. labedae (PV639361). Among them, the extract from S. vinaceusdrappus SJ5 stood out, showing strong antibacterial activity across nearly all tested pathogens. Minimum inhibitory concentrations ranged from 6.25 to 25 mg/mL, and the extracts significantly disrupted biofilm formation. GC-MS analysis of the S. vinaceusdrappus extract revealed several bioactive compounds with reported antibiofilm properties, including 9,12,15-octadecatrienoic acid methyl ester, pentaacetate, and hexadecanoic acid methyl ester. ConclusionActinomycetes of the genus Streptomyces isolated from date palm soils demonstrate promising antibacterial and antibiofilm activity, offering potential for developing new agents to combat resistant bacterial pathogens.