88D-26

The objective of this work was to study the antifungal effects of Lactobacillus rhamnosus and Bacillus pumilus, which had previously exhibited strong antifungal properties in agar media. Live bacterial cells and their cell-free supernatants were tested against strains of Aspergillus, Penicillium, and Fusarium in liquid media.

The simultaneous antagonism assay, measuring reduction of mycelium weight, was used to detect antifungal activity. Initially, MRS, PD, and YES broths, were compared for the production of antifungal substances by live cells of the two bacteria.

It was observed that L. rhamnosus exhibited stronger antifungal properties in MRS broth than in YES broth. In MRS broth, L. rhamnosus inhibited mycelial growth of A. niger, P. digitatum, and F. subglutinans, by 96.8%, 90.5%, and 96.0%, respectively. On the other hand, B. pumilus exhibited stronger inhibitory activity in YES than in PD broth. Mycelium growth of the three molds in YES broth was inhibited by B. pumilus by 95.5, 85.0, and 29.4%, respectively. Secondly, results obtained for inhibition of mold growth by the live bacterial cells, were compared to inhibitory activity of bacterial cell-free supernatants. It was found that live bacterial cells were able to inhibit mold growth and spore production to a greater extent than the cell-free supernatants. However, growth and spore production by all three mold strains were inhibited to some degree when cell-free supernatants of L. rhamnosus and B. pumilus were used as growth media. Cell-free supernatant of L. rhamnosus showed stronger inhibitory activity than cell-free supernatant of B. pumilus, inhibiting mycelial growth of A. niger, P. digitatum, and F. subglutinans, by 84.0%, 91.6%, and 48.7%, respectively.

These results suggest that both bacterial strains have potential as biocontrol agents of molds.