Ultrastructural evidences of growth inhibitory effects of a novel biocide, Akacid(plus), on an aflatoxigenic Aspergillus parasiticus.

The effects of Akacid(plus), a novel member of guanidine-based polymeric compounds recently introduced as a potent inhibitor of fungal growth and aflatoxin biosynthesis were studied on Aspergillus parasiticus by transmission electron microscopy (TEM). The toxigenic fungus was cultured on yeast extract-sucrose broth in presence of serial two-fold concentrations of Akacid(plus) (1.5-96 microL/50 mL medium) for 96 h at 28 degrees C with shaking. Mycelial samples exposed to fungistatic concentrations of compound (1.5-48 microL) were processed for TEM. Corresponding to the growth inhibition, TEM observations revealed morphological anomalies in fungal compartments. The results demonstrated that Akacid(plus) targets the plasma membrane of the hyphae by its breaking down at variable intervals with the formation of small membrane-bound vesicles inside the cytoplasm, while no obvious damage was observed on the cell wall. A marked depletion of cytoplasmic contents of hyphae accompanied with lysis and disruption of membranes of major organelles such as nuclei, mitochondria and endoplasmic reticulum indicates that in high fungistatic concentrations, Akacid(plus) passes not only through the cell wall but also through the plasma membrane and then interact with membranous structures of the cytoplasmic organelles. Ultrastructural changes of fungal compartments exposed to Akacid(plus) in relation to the fungal growth and aflatoxin biosynthesis are discussed.

Inhibitory effects of Akacid (plus) on growth and aflatoxin production by Aspergillus parasiticus.

The effects of Akacid plus, a novel guanidine-based polymer first introduced as a biocidal and disinfectant agent were studied on Aspergillus parasiticus growth and its aflatoxin (AF) productivity. The fungus was cultured on yeast extract-sucrose (YES) broth in presence of various twofold serial dilutions of 25% Akacid plus (1.5-96 microL/50 mL medium) and then incubated in shaking condition with 150 rev./min at 28 degrees C for 96 h. Based on obtained results, Akacid plus was found to significantly inhibit both growth and aflatoxin B1 (AFB1) synthesis in very low concentrations in a dose-dependent manner. Fungal growth inhibition was determined in the range of 9.6-99.6% in mycelia exposed to the total concentration range of 1.5-48 microL. A final concentration of 96 microL was necessary to completely inhibit the growth of fungus. Under similar conditions, AFB1 synthesis was found to be strongly inhibited by 8.1-98.0% in presence of 1.5-24 microL Akacid plus with a maximum of 100% by 48 microL concentration. With respect to the unique physico-chemical properties of Akacid plus, its marked inhibitory effects on A. parasiticus growth and its AFB1 synthesis shown for the first time in this study make it a promising candidate for application in prevention programmes of AF contamination of susceptible crops.