Actinomycetes bacteria are an inexhaustible natural source of secondary metabolites with diverse antimicrobial activities. In the current study, screening based on antimicrobial activity of the cell-free supernatant (CFS) of 23 actinomycetes isolates from Atlas forest soils in Northeastern Algeria was performed against ten human bacterial pathogens and Candida albicans ATCC 10231 strain. Among them, three isolates AM138DZ, AM141DZ and AM183DZ showed antagonistic effects towards indicator pathogens. The isolate AM183AZ exhibited strong activities against Staphylococcus aureus ATCC 6538, C. albicans ATCC 10231, clinical strains Esherichia coli BLSE and Salmonella spp. BLSE. The isolates AM141AZ and AM138AZ displayed high antimicrobial activity towards C. albicans 10231. Interestingly, the CFS of AM138DZ and AM141DZ combined with amoxicillin inhibited β-lactamase activity from Klebsiella pneumoniae ATCC 700603, an extended-spectrum β-lactamase producing strain. The ethyl acetate extracts of the three isolates displayed a large spectrum of antimicrobial activity against all pathogens tested. Analysis of their contents by UPLC-ESI-MS/MS revealed the identification of 16 to 18 compounds, among them 5 flavonoids, 6 organic acids and 2 phenols. Overall, flavonoids (such as rutin, chrysin, quercetin and catechin) were the major compounds detected in the three extracts. Depending on the isolate, other notable compounds were detected at significant levels: β-caroten, salicin and salycilic acid. Molecular identification of the three isolates using 16S rRNA sequence homology suggested that these isolates should be assigned as Streptomyces flavogriseus AM138DZ, Streptomyces felleus AM141DZ, and Streptomyces rubiginosohelvolus AM183DZ strains. Our study provides a promising natural alternative source of antimicrobials and β-lactamase inhibitors in particular.
Keywords: Actinomycetes; Antimicrobials; Soil; Β-lactamase inhibitors.
© 2025. The Author(s), under exclusive licence to Springer Nature B.V.