Antibacterial activity of mangrove-derived Streptomyces pseudogriseolus NELs-50 against methicillin-resistant Staphylococcus epidermidis

Abstract

Background: Methicillin-resistant Staphylococcus epidermidis (MRSE) represents a growing healthcare threat, necessitating novel antimicrobial agent development. Mangrove-derived Streptomyces species offer promising potential as sources of bioactive compounds against drug-resistant pathogens. Objective: To isolate and characterise a mangrove-derived Streptomyces isolate with anti-MRSE activity and identify its bioactive metabolites. Methods: Mangrove soil samples were screened for anti-MRSE activity. Isolate NELs-50 was identified through morphological, biochemical, and 16S rRNA gene sequencing. Fermentation parameters were optimised, bioactive metabolites extracted with organic solvents, and characterised using gas chromatography-mass spectrometry (GC-MS). Minimum inhibitory concentration (MIC) and stability assessments were conducted. Results: NELs-50 was identified as Streptomyces pseudogriseolus (99% sequence similarity) with potent anti-MRSE activity (28.67 mm inhibition zone). Culture conditions were optimised for maximum antimicrobial production. Ethyl acetate extract showed highest activity (28.83 mm). The extract retained 41% activity at 121 °C, tolerated pH 2–12, and resisted enzymatic degradation. Gas chromatography-mass spectrometry analysis identified nine compounds, with major components being pyrrolo[1,2-a]pyrazine derivatives (100% peak area), and 2,4-Di-tert-butylphenol (12.64%). Minimum inhibitory concentration against MRSE was 125 µg/mL. Conclusion: S. pseudogriseolus NELs-50 shows promising anti-MRSE activity and produces putative bioactive metabolites with broad pH tolerance but reduced activity at elevated temperatures, supporting its potential as a source of antimicrobial lead compounds. What this study adds: This study reports the isolation and characterisation of S. pseudogriseolus NELs-50 from Hainan mangroves. The ethyl acetate extract showed broad pH tolerance but was heat-sensitive at elevated temperatures, retaining only 41% activity after treatment at 121 °C. Gas chromatography-mass spectrometry analysis identified nine putative metabolites, suggesting that NELs-50 may serve as a promising source of antimicrobial lead compounds against multidrug-resistant pathogens.