tailieunhanh - Fungicides for Plant and Animal Diseases Part 5

Tham khảo tài liệu 'fungicides for plant and animal diseases part 5', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Naturally Occurring Antifungal Agents and Their Modes of Action 71 Further support for the surfactant postulate was also obtained in experiments that showed a rapid decline in the number of viable cells after the addition of undecanol at the exponential growth-phase as shown in Figure 11. In addition the effect of undecanol was tested during holding viable cell number in the presence of cycloheximide. This drug is known to restrict cell division by inhibiting protein synthesis its effect against S. cerevisiae cells is fungistatic. Undecanol rapidly killed S. cerevisiae cells in which cell division was inhibited by cycloheximide. This observation excludes several modes of action for undecanol such as inhibition of DNA RNA protein or cell wall component synthesis in vivo. The result observed indicates that the antifungal mechanism of undecanol is due primarily to its surfactant property although it is not possible to confirm that membrane damage is the only cause of the lethal effect. It can be concluded that the medium-chain alkanols target in part the extracytoplasmic region as surfactants. This conclusion is highly desirable since they do not need to enter the cell thus avoiding most resistance mechanisms based on cellular pump. After 104 cells were incubated in ME broth for 14 h compounds were added as follows 50 ug ml. cycloheximide 25 ug mL undecanol no compound . After further 2-h incubation undecanol was added in cycloheximide treated cells O . Fig. 11. Fungicidal effect of undecanol in cycloheximide treated cells. The time-kill curve study showed that undecanol was fungicidal against S. cerevisiae at any growth stage. Figure 12 shows the effect of undecanol at various growth stages. Undecanol at MFC rapidly reduced the number of viable cells when added to the culture at the exponentially growing culture 106 CFU mL within the first 4 h. Thus no viable cells were detected within 2 h after adding undecanol. However undecanol was not fungicidal when added to the