Antimicrobial activity of endophytic actinomycetes isolated from the root of Zingiber officinale Rosc.

Abstract

Endophytic actinomycete metabolites have the potential to be used in medical applications such as antibiotics and antifungals. Furthermore, it is a significant source of antimicrobial compounds for combating antibiotic-resistant microorganisms such as MRSA (Methicillin-resistant Staphylococcus aureus). Zingiber officinale Rosc is very common in Vietnam, particularly in Ho Chi Minh City, and it is known to contain various bioactive compounds and have antimicrobial activity. This study aimed to isolate endophytic actinobacteria, especially Streptomyces spp., from Zingiber officinale Rosc grown in Vietnam and to screen for their ability to produce antibacterial metabolites. Zingiber officinale Rosc roots were surface-sterilized, then cultured on inorganic salt starch agar (ISP4) and actinomycete isolation agar (AIA). Subculture was performed to obtain pure strain. Isolates with actinomycetes-like morphology observed via gram-staining were selected and cultured in broth for ethyl acetate extract, then the antimicrobial activity of the extract was evaluated using agar-well diffusion testing. Then, strains with high antimicrobial activity were subjected to identification using 16S rRNA sequencing. As a result, twenty-eight isolates were selected among two selective media through gram-staining. The agar well diffusion test showed seven isolates with antimicrobial potential, there were 4.7, 4.11 strains against S. aureus, 4.11 strains against E. coli, 4.5 and 4.7 strains against B. subtilis, and 4.6 and 4.9 strains against P. aeruginosa. Among seven strains identified with 16S rRNA sequencing, four were Streptomyces griseorubiginosus and three were Microbispora hainanensis. In conclusion, twenty-eight endophytic actinomycetes-like isolates were isolated from the root of Zingiber officinale Rosc. Among those, seven isolates showed moderate to high antimicrobial activity. Seven isolates with high antimicrobial activity were identified and they were Streptomyces griseorubiginosus and Microbispora hainanensis.