A new Streptomyces strain isolated from Saharan soil produces di-(2-ethylhexyl) phthalate, a metabolite active against methicillin-resistant Staphylococcus aureus

An actinomycete strain designated G60 was isolated from a Saharan soil sample in Ghardaïa, Algeria, by a dilution agar plating method using chitin-vitamin agar medium supplemented with penicillin. Morphological and chemical studies indicated that this strain belonged to the genus Streptomyces. Analysis of the 16S rDNA sequence showed an identity level within Streptomyces species, with S. coerulescens ISP 5146T and S. bellus ISP 5185T the most closely related (100 % for each). However, the comparison of the morphological and physiological characteristics of the strain with those of the two nearest species showed significant differences. Strain G60 had a very strong activity against pathogenic staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, other clinical isolates of MRSA and vancomycin resistant S. aureus (VRSA) S1. One antimicrobial compound was extracted by n-hexane from the ISP2 culture medium at 5 days of fermentation culture and purified by HPLC. The chemical structure of the compound was determined after spectroscopic (1H NMR, 13C NMR, 1H-1H COSY and 1H-13C HMBC spectra), and spectrometric (mass spectrum) analyses. The bioactive compound was identified as di-(2-ethylhexyl) phthalate.