Marine Bacillus pumilus substances exhibit antimicrobial effect on multidrug-resistant Staphylococcus aureus

Aims: This study aimed to assess the antimicrobial potential of Bp1-AdE, produced by Bacillus pumilus 64-1, and to investigate its mode of action against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). Methods and results: Bp-1AdE, derived from sponge-associated B. pumilus, exhibited bactericidal activity at 1 550 mu g ml (-1) against S. aureus ATCC29213 and MRSA strains. Light and fluorescence microscopy revealed drastic cell lysis of S. aureus treated with Bp-1AdE. Scanning and transmission electron microscopy suggested that Bp-1AdE disrupts the cytoplasmic membrane. Toxicity assays showed that Bp-1AdE was non-toxic to Tenebrio molitor larvae. Liquid chromatography-mass spectrometry and Global Natural Product Social spectral libraries identified four substances within Bp-1AdE, including aliphatic alcohols [3,4-dipentylhexane-2,5-diol and 1,1'-(4,5-dibutyl-3,6-dimethylcyclohexane-1,2- diyl)bis(ethan-1-one)] and terpenoids (cholic acid and canrenone). Conclusions: Bp-1AdE demonstrated selective toxicity and bactericidal activity, highlighting its potential for controlling infections caused by multidrug-resist ant S . aureus strains.