Free chlorine and phytic acid synergistically inactivated conidia of Aspergillus spp.

Chlorination has been widely used to disinfect various microbials in the environment, but its fungicidal activity is known to be limited. Here, we demonstrate that a combinatorial treatment with free chlorine and phytic acid exerted high fungicidal activities against selected species of Aspergillus. Treatment with either chlorine (7 mg/l) or phytic acid (∼400 mg/l) without pH adjustment caused marginal inactivation of Aspergillus niger conidia within 5 min. However, the combinatorial treatment with free chlorine and phytic acid inactivated 98% of A. niger conidia within 5min (C¯T=25.7mg/l·min). Overall fungicidal efficiency of combinatorial application was higher (∼256%) than the sum of inactivation levels by individual treatment, suggesting a synergistic effect between free chlorine and phytic acid. Transmission electron microscopy observation showed that free chlorine primarily disrupted nucleo-cytosolic organs, whereas phytic acid preferentially disintegrated the cell wall and plasma membrane. The combination of both agents demolished the conidial structure of A. niger. The effects of these chemicals on the cell membrane were verified with propidium iodide staining, lipid peroxidation, and extracellular ATP secretion. Fungicidal activities of chlorine and phytic acid were further confirmed against A. parasiticus and A. flavus. Our data suggest that the mixture of free chlorine and phytic acid without any additional preparation may efficiently disinfect Aspergillus spp. through the synergistic activities of individual components.