The macrocyclic peptide antibiotic micrococcin P-1 is secreted by the food-borne bacterium Staphylococcus equorum WS 2733 and inhibits Listeria monocytogenes on soft cheese

Staphylococcus equorum WS 2733 was found to produce a substance exhibiting a bacteriostatic effect on a variety of gram-positive bacteria. The metabol ite was purified to homogeneity by ammonium sulfate precipitation and semip reparative reversed-phase high-performance liquid chromatography. Electrosp ray mass spectrometry confirmed the high purity of the compound and reveale d a molecular mass of 1,143 Da, By two-dimensional nuclear magnetic resonan ce spectroscopy the substance was identified as micrococcin P-1 which is a macrocyclic peptide antibiotic that has not yet been reported for the genus Staphylococcus. A total of 95 out of 95 Listeria strains and 130 out of 13 5 other gram-positive bacteria were inhibited by this substance, while none of 37 gram-negative bacteria were affected. The antilisterial potential of this food-grade strain as a protective starter culture was evaluated by it s in situ application in cheese-ripening experiments under laboratory condi tions. A remarkable growth reduction of Listeria monocytogenes could be ach ieved compared to control cheese ripened with a nonbacteriocinogenic type s train of Staphylococus equorum, In order to prove that inhibition was due t o micrococcin P-1, a micrococcin-deficient mutant was constructed which did not inhibit L. monocytogenes in cheese-ripening experiments.