Antimicrobial activity of Streblus asper leaf extract.

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.

Cells of different ploidy are often present together in Cryptococcus neoformans strains.

We examined the ploidy of C. neoformans strains using both laser scanning cytometry and a fluorescence microscope equipped with a photomultiplier. Haploid strains consisted of normal-sized cells with a haploid DNA amount. In the cell population there were also large-sized cells with a diploid DNA amount. These large cells in haploid strains were isolated using a Skerman micromanipulator, cultivated, and were able to generate diploid clones. Even after only 3-5 transfers on slants, haploid cells were present in all the diploid clones examined. Conversely, haploid clones obtained by single-cell-isolation of normal-sized cells from haploid strains were also shown to contain diploid cells after 3-5 transfers. Fresh haploid isolates from the environment similarly contained diploid cells after 3-5 transfers. Thus, a cellular ploidy shift was shown to occur widely in C. neoformans strains.

Oxidative stress sensitivity and superoxide dismutase of a wild-type parent strain and a respiratory mutant of Candida albicans.

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.

Epidemiological study on contamination of water and diarrheal diseases in a rural community in northeast Thailand.

An epidemiological and bacteriological study of diarrheal diseases as well as the relation between domestic-use water and passage of enteric pathogens with stools of the villagers was performed in the northeastern rural area of Thailand on 4 different occasions during the 3 years from 1992-1994. The questionnaire study indicated that 93% of the residents used rain water stored in containers for drinking and other domestic uses, and that 28% of them filtrated and/or boiled the water before drinking it. About 90% of drinking water samples collected from the same residents showed positive responses for the preliminary test ofEscherichia coli contamination. Furthermore, a precise bacteriological survey indicated that more than half of the drinking water samples collected from containers storing rain water were contaminated with various enteropathogenic bacteria, includingE. coli, Vibrio spp. andShigella spp. The new serotype ofV. cholerae O139, synonym 'Bengal cholerae,' which could be isolated from different specimens, is replacing the traditional species ofVibrio. Forty-one per cent of the villagers carried enteropathogenic bacteria in their stools. Most of them were asymptomatic carriers and only a few of them showed clinical features of diarrhea. A few concrete propositions were discussed to supply safe water in these areas where drinkable underground water is not available.

Isolation of Campylobacters from the canals of Bangkok metropolitan area.

The 100 ml of canal water samples of 36 canals in Bangkok Metropolitan Area were examined in three periods starting from July-September 1988, November 1988-January 1989 and February-April 1989. Each time the 52 water samples were checked. Of 156 water samples, 116 strains of Campylobacter species were isolated. They were 63.79 per cent (74 strains) of C. cryaerophila and 36.21 per cent (42 strains) of C. cryaerophila-like organisms. The differentiation was determined by urease activity test. C. cryaerophila was isolated from 44.23 per cent (23 strains), 51.19 per cent (27 strains) and 46.15 per cent (24 strains) and also C. cryaerophila-like organism from 28.85 per cent (15 strains), 19.23 per cent (10 strains) and 32.69 per cent (17 strains) of the 52 samples during each period respectively. Since C. cryaerophila and C. cryaerophila-like are aerotolerant Campylobacter, they grow well in aerobic conditions at 25 degrees-36 degrees C. On the contrary, thermophilic Campylobacter such as C. jejuni, C. coli and C. laridis require atmosphere containing 5 per cent O2, 10 per cent CO2, 85 per cent N2 and temperature at 36 degrees-42 degrees C, so the environment in the canals is unfavorable for their growth. The etiological role of C. cryaerophila in pathogenesis in humans is still unknown, and requires furthers study. This study shows that canals can be an important source of these two Campylobacter species that might be potential pathogens in the future.

Aetiologic agents of septic sore throat in Thai children.

A bacteriological study of children with respiratory infections in Bangkok during January to November 1976 revealed that 37% of the patients had symptoms and sign of bacterial pharyngotonsillitis. Twenty-six per cent of these children harboured Streptococcus pyogenes in their throats. The numbers of streptococci other than group A and Staphylococcus aureus were increased in the children with respiratory infections. However, Staph. aureus was found as the sole organism in children with exudate more often than in the children with only URI. The possible role of Staph. aureus in bacterial pharyngitis should not be ignored. Penicillin remains a drug of choice for the treatment of streptococcal pharyngitis. If penicillin is contraindicated, erythromycin should be preferred over lincomycin as a second choice of drug in order to avoid treatment failure if lincomycin resistant streptococci are present.