Received: 14 January 2012                                                               Revised accepted: 11 August 2012

Purpose: To isolate and identify an antibiotic produced by a soil bacterium, Intrasporangium strain N8, with antibacterial activity against both Gram-positive and Gram-negative bacteria.

Methods: Fermentation followed by extraction using a three-solvent system (petroleum ether, acetone and ethyl acetate) and pH precipitation, successfully separated the antibiotic complex from the culture broth. Purification was carried out using flash column chromatography (FCC), thin-layer chromatography (TLC) and reverse phase high performance liquid chromatography (HPLC). The identities of the molecules were elucidated by gas chromatography-mass spectrometry (GC-MS) analysis.

Results: Three main components of the antibiotic were isolated and identified as 4-methyl-3-penten-2-one, 4-hydroxy-4-methyl-2-pentanone and N-acetyltryptamine. Bioassay results showed activity against both mammalian and plant pathogenic bacteria including Pseudomonas fluorescens, Xanthomonas campestris pv campestris, Escherichia coli and Serratia marcescens. Pseudomonas fluorescens (MIC = 0.0625 μg/ml) and Xanthomonas campestris pv campestris (MIC = 0.0026 μg/ml) represent the two plant pathogenic genera that are notoriously difficult to contain in the field.

Conclusions: Since the antibiotic isolated during this study showed activity against both mammalian and plant pathogenic bacteria, it is hoped that this work will encourage further investigation in this field. This antibiotic could become very useful as an agricultural bacteriocide against some resistant plant pathogens.