Synergistic action of nikkomycins X and Z with papulacandin B on whole cells and regenerating protoplasts of Candida albicans.

Combinations of nikkomycin X (NX) or nikkomycin Z (NZ), known inhibitors of chitin synthesis in fungi, together with papulacandin B (PB), an inhibitor of beta-glucan synthesis, were tested for synergistic activity against four isolates of Candida albicans by using the broth microdilution checkerboard technique and a method to assess the regeneration of cell wall material in protoplasts. The construction of isobolograms from the data generated by the checkerboard determinations revealed a synergistic effect for the two classes of compounds against all strains. The combination of NX and PB was more effective than the combination of NZ and PB, perhaps reflecting the lower Ki value of NX. While the presence of NX and NZ reduced chitin synthesis, as determined by staining with calcofluor white and assaying with a microfluorimeter, cells treated with PB demonstrated an increased synthesis of chitin. Protoplast regeneration experiments using similar concentrations of the two classes of compounds resulted in comparable findings. The combination of NX and PB resulted in a greater inhibition of chitin synthesis than did equivalent combinations of NZ and PB. These data suggest that combinations of agents active against cell wall synthesis in fungi may prove more useful as chemotherapeutic agents than such compounds used singly.