Isolation of marine actinomycetes with antibacterial activity from Hai Phong marine environments, Vietnam

Abstract

Marine actinomycetes represent a promising source of novel bioactive compounds, yet the coastal environments of Hai Phong, Vietnam, remain largely unexplored. This study aimed to isolate and evaluate the antibacterial potential of marine actinomycetes from coastal sand and seawater samples in Hai Phong, with subsequent morphological, physiological, and 16S rRNA gene sequence identification of the strain with the highest antibacterial activity. A total of 36 actinomycete strains were isolated and screened for antibacterial activity using the agar well diffusion method against nine reference strains. Of these, 23 strains (63.9%) exhibited antibacterial activity, predominantly against Gram-positive bacteria. Strain HP30 was demonstrated the strongest activity, produced inhibition zones of 25 mm against Staphylococcus aureus CCARM 3090 (MRSA) and 25 mm against Salmonella enterica ATCC 14028. Its crude ethyl acetate extracts also retained potent activity, with inhibition zones of 23 mm and 21 mm against the same pathogens, respectively. Phylogenetic analysis was based on 16S rRNA gene sequencing identified HP30 as closely related to Streptomyces parvulus (99.84% similarity). Morphological, physiological, and biochemical characterization further supported its taxonomic position. These findings highlight the antibacterial potential of marine actinomycetes isolated from Hai Phong coastal environments. Strain HP30, identified as closely related to Streptomyces parvulus, produced potent in vitro inhibition against several indicator strains, including MRSA, both in culture supernatant and crude ethyl acetate extract. Further chemical characterization of its active metabolites is warranted.