Antimicrobial action of roquefortine.

Roquefortine, a secondary metabolite of Penicillium roqueforti, was investigated with regard to its effect on microorganisms. The growth of gram-positive bacteria was inhibited by roquefortine, whereas gram-negative bacteria were not influenced at all. The minimal inhibitory concentrations for gram-positive organisms were about 80 micrograms/mL cells on the average. The sensitive bacterium Corynebacterium flaccumfaciens was chosen for characterizing the antimicrobial action of the mycotoxin. Addition of low roquefortine concentrations at the beginning of bacterial growth resulted in prolongation of both the lag and logarithmic phases. High toxin concentrations (100 micrograms/mL cells) added to growing cells caused prolongation of logarithmic growth and decreased maximum cell density. This effect could be abolished when the cells, inhibited during the logarithmic growth, were centrifuged, washed, and transferred into fresh nutrient medium. In that case a second prolonged lag phase occurred, but the following logarithmic growth was comparable to normal cell growth. These results indicate that the antimicrobial effect of roquefortine is bacteriostatic but not bactericide. The growth inhibition might be a consequence of a roquefortine influence on bacterial respiration. The uptake of oxygen was reduced to 50% at a toxin concentration of 100 micrograms/mL cells.