Ahmed E. Yousef

Incorporation of [14C] acetate into aflatoxin by resting cultures of Aspergillus parasiticus in the presence of antifungal agents

SummaryResting cultures of Aspergillus parasiticus were treated with sorbic acid (200 ppm), Nα-palmitoyl-l-lysyl-l-lysine ethyl ester dihydrochloride (PLL) (300 ppm), nisin (30 ppm), nystatin (30 U/ml), dichlorvos (9 ppm), butylated hydroxyanisole (BHA) (30 ppm) and isoprothiolane (30 ppm). Incorporation of [14C]acetate into aflatoxins B1 and G1 by the mold in the presence of these antifungal agents was measured after 12 h of agitated incubation at 28°C. Nystatin and BHA effectively inhibited incorporation of the label into aflatoxin B1 (73.1 and 56.9%) and G1 (68.9 and 91.6%), respectively, whereas PLL and nisin, at the levels used, were less effective. Sorbic acid caused greater inhibition of de novo synthesis of aflatoxin B1 than of G1 while isoprothiolane exhibited the opposite effect. Because the compounds tested had dissimilar physical, chemical and antimicrobial properties, it is likely that they inhibited synthesis of aflatoxin by different mechanisms. Generally, inhibition of aflatoxin synthesis by the test chemicals under resting conditions was more pronounced than what was reported earlier when the same chemicals (at the same levels) were tested with growing cultures of the mold.

Growth and Biosynthesis of Aflatoxin by Aspergillus parasiticus in Cultures Containing Nisin

ZusammenfassungNisin (200 oder 5000 Reading-Einheiten/ml) wurdeAspergillus parasiticus Kulturen zugegeben. Die Kulturen wurden bei 28 °C für 3, 7 oder 10 Tage bebrütet und auf Mycel-Trockengewicht, pH und Aflatoxin-Inhalt geprüft. Während der ersten drei Tage wurden das Wachstum und die Aflatoxin-Biosynthese durch Nisin etwas gehemmt, nach längere Incubation jedoch gefördert.SummaryNisin, 200 or 5000 Reading units/ml, was added toAspergillus parasiticus cultures. The cultures were incubated at 28 °C for 3, 7 or 10 days and analyzed for mycelial dry weight, pH and accumulation of aflatoxin B1 and G1. During the first 3 days of incubation, dry weight, pH decrease and aflatoxin accumulation were suppressed by nisin, when compared with similar values for the nisin-free control. After longer incubation, differences in dry weight and pH values decreased, whereas accumulation of aflatoxin in the nisin-containing cultures surpassed that of the control.