Bactericidal activity was found in the 50% ethanol (v/v) extract of Streblus asper leaves. The extract possessed a selective bactericidal activity towards Streptococcus, especially to Streptococcus mutans which has been shown to be strongly associated with dental caries. The extract had no effect on cultures of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, Staphylococcus coagulase positive, Staphylococcus coagulase negative, Serratia marcescens, Klebsiella pneumoniae, Enterobacter, Pseudomonas aeruginosa, Burkholderia pseudomeallei and Candida albicans. The minimum growth inhibitory concentration and the minimum bactericidal concentration of S. asper extract against 10(8) CFU/mL of S. mutans was 2 mg/mL. The active compound is partially polar, partially heat labile, precipitated by 80% ammonium sulphate, and possesses a molecular weight larger than 10 000 Da. The potential for using S. asper extract as a natural product for controlling dental caries is discussed.

No abstract

It is important to know responses of the pathogenic fungi to reactive oxygen species by which hosts protect themselves against fungal infection. In the present study, sensitivities to the superoxide radical (O2-) and superoxide dismutase (SOD) were compared between a wild-type parent strain and a respiration-deficient mutant of Candida albicans. When their survival was examined on an agar medium containing an intracellular O2- generator, paraquat (PQ), the parent strain was selectively killed by increasing the PQ concentration. In contrast, when cells of both strains were illuminated in a riboflavin solution, they exhibited similar sensitivity to O2- generated extracellularly by photo-reduced riboflavin. There were no large differences in sensitivity to hydrogen peroxide in the two strains. Thus, the high tolerance of the mutant to PQ was suggested to result from low intracellular O2- generation by PQ due to the respiratory deficiency. It is generally accepted that fungal cells contain manganese (Mn)-SOD in the mitochondria and copper and zinc (CuZn)-SOD in the cytoplasm. Cyanide-insensitive SOD activity (attributable to Mn-SOD) was dominant in the parent strain throughout growth phases, whereas cyanide-sensitive activity (attributable to CuZn-SOD) occurred in the mutant. The activity bands of Mn- and CuZn-SODs were clearly separated by electrophoresis of the cell extracts of both strains on non-denaturing polyacrylamide gels. The electrophoretic profiles obtained were consistent with the results of the activity assay. These results showed that the respiratory deficiency affected oxidative stress sensitivity and SOD in C. albicans.

We examined the ploidy of C. neoformans strains using both laser scanning cytometry and a transfers. Thus, a cellular ploidy shift was shown to occur widely in C. neoformans strains.

It is important to know responses of the pathogenic fungi to reactive oxygen species by which hosts protect themselves against fungal infection. In the present study, sensitivities to the superoxide radical (O2−) and superoxide dismutase (SOD) were compared between a wild‐type parent strain and a respiration‐deficient mutant of Candida albicans. When their survival was examined on an agar medium containing an intracellular O2− generator, paraquat (PQ), the parent strain was selectively killed by increasing the PQ concentration. In contrast, when cells of both strains were illuminated in a riboflavin solution, they exhibited similar sensitivity to O2− generated extracellularly by photo‐reduced riboflavin. There were no large differences in sensitivity to hydrogen peroxide in the two strains. Thus, the high tolerance of the mutant to PQ was suggested to result from low intracellular O2− generation by PQ due to the respiratory deficiency. It is generally accepted that fungal cells contain manganese (Mn)‐SOD in the mitochondria and copper and zinc (CuZn)‐SOD in the cytoplasm. Cyanide‐insensitive SOD activity (attributable to Mn‐SOD) was dominant in the parent strain throughout growth phases, whereas cyanide‐sensitive activity (attributable to CuZn‐SOD) occurred in the mutant. The activity bands of Mn‐ and CuZn‐SODs were clearly separated by electrophoresis of the cell extracts of both strains on non‐denaturing polyacrylamide gels. The electrophoretic profiles obtained were consistent with the results of the activity assay. These results showed that the respiratory deficiency affected oxidative stress sensitivity and SOD in C. albicans.