Antifungal activities and effect of Lactobacillus casei AST18 on the mycelia morphology and ultrastructure of Penicillium chrysogenum

The antifungal effects of Lactobacillus casei AST18 on Penicillium chrysogenum. were investigated. Viable bacteria were used to detect the minimum inhibitory concentration of lactic acid bacteria (102 CFU/mL) to inhibit the growth of P. chrysogenum. Results showed that L. casei AST18 inhibited the growth of P. chrysogenum. The mycelial morphology was also altered. The scanning electron microscopy images of P. chrysogenum exposed to L. casei AST18 further showed that the mycelia were collapsed and appeared transparent. Numerous clots were also observed in the fungal cytoplasm. The tip of the hypha was deformed and exhibited a moniliform or inflated shape. The transmission electron microscopy images of L. casei AST18-exposed P. chrysogenum showed the occurrence of autophagy and death of fungal cells. Changes in the morphological characteristics of P. chrysogenum were observed in the antifungal activity experiment with viable bacteria, but such changes were not evident in the cell-free culture filtrate of L. casei AST18. This bacterial strain showed high antifungal activities and could be used as a fungal inhibitor in food and medicine.