Identification of Streptomyces sp. AMLK-335 producing antibiotic substance inhibitory to vancomycin-resistant enterococci

Abstract

The actinomycete strain AMLK-335 was antagonistic to vancomycin-resistant enterococci (VRE). Based on the diaminopimelic acid (DAP) type, and morphological and physiological characteristics revealed by scanning electron microscopy (SEM), AMLK-335 was confirmed to belong to the genus Streptomyces. Analysis of the 16S rDNA nucleotide sequences found AMLK-335 to have a relationship with Streptomyces platensis. The production of antibiotic from this strain was most favorable when cultured on glucose, polypeptone, yeast extract (PY) medium for 6 days at 27 °C. The antibiotic was identified as cyclo(L-phenylalanyl-L-prolyl) by comparing it with the reported MS and NMR spectral data. Cyclo(phe-pro) from the PY cultures of AMLK-335 was most effective against the VRE strains E. faecium (K-98-637) and E. faecalis (K-98-258). Furthermore, cyclo(phe-pro) had antimicrobial activity against Bacillus subtilis, Microcuccs luteus, Staphylococcus aureus, and Saccharomyces cerevisiae, but it was ineffective against Candida albicans, Streptomyces murinus, and Aspergillus niger.