RESUMEN
AIMS: Assessment of antimicrobial activity of the mycoparasite Coniothyrium minitans and its macrolide antibiotic macrosphelide A. METHODS AND RESULTS: Thirteen isolates of C. minitans were tested for ability to inhibit a number of filamentous fungi, yeasts, oomycetes and bacteria in agar based tests. Activity was found against some ascomycetes, basidiomycetes, oomycetes and Gram-positive bacteria, but not against zygomycetes, yeasts or Gram-negative bacteria tested. Six C. minitans isolates (Conio, Contans, IVT1, CM/AP/3118, B279/1, A1/327/1) were found to produce macrosphelide A in liquid culture and no other antibiotics were detected. On agar, macrosphelide A inhibited growth of some ascomycetes, basidiomycetes, oomycetes and all four Gram-positive bacteria tested, including the medically important Staphylococcus aureus with a minimum inhibitory concentration of < or =500 microg ml(-1). There was no inhibition observed against the yeasts and Gram-negative bacteria when macrosphelide A was tested at 700 microg ml(-1). CONCLUSIONS: The spectrum and level of activity of macrosphelide A produced by C. minitans against micro-organisms are extended markedly compared to previous reports. SIGNIFICANCE AND IMPACT OF THE STUDY: Macrosphelide A was effective against Staph. aureus. Further study on the control of this bacterium is merited in view of the development of antibiotic resistance.