RESUMEN
This research comparatively investigates the in vitro antimicrobial activity of extracts from Nymphaea pubescens (pink water lily) leaves against pathogenic bacteria. The experimental extracts are aqueous, acetonic, and 95% ethanolic N. pubescens extracts; and the pathogenic bacteria being studied include Aeromonas hydrophila, Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio harveyi, which are commonly found in freshwater fish and brackish aquatic animals. The ethanolic N. pubescens extract achieves the highest bacterial inhibitory effects against V. parahaemolyticus and V. vulnificus. The minimum inhibitory concentrations of the ethanolic extract against A. hydrophila and V. harveyi are 10 mg/mL; and 2.5 mg/mL against V. parahaemolyticus and V. vulnificus. The ethanolic N. pubescens extract is effective against V. parahaemolyticus. The high-performance liquid chromatography results show that, in the phenolic acids group, gallic acid is the most dominant (0.600-3.21% w/w), followed by sinapic acid (0.37-0.83% w/w). In the flavonoids group, catechin is the most dominant (0.02-1.08% w/w), followed by rutin (0.002-0.03% w/w). Essentially, the ethanolic N. pubescens extract can potentially be used as a natural antibiotic agent to treat bacterial infections in fish and aquatic animals.
RESUMEN
Investigations on the water quality of the Mae Klong River and Estuary were conducted from April 2005 to February 2006 during periods of early-, mid-, and late-loading. Nutrient loads and transfer patterns were studied together with clarification of contaminated sites. The results indicated that NH4+, NO2- + NO3-, Si(OH)4 and PO4(3-) concentrations varied by season and were comparatively high in the mid-loading period. Analysis of DIN:P and Si:P molar ratios indicated that P04(3-) could possibly be a limiting nutrient. Highly contaminated sites were in the middle (Ratchaburi province) and lower (Samut Songkhram province) river zones in which anthropogenic wastewater discharges were significantly (p < 0.05) loaded. Analysis of the DIN and P transfer patterns showed that self-remediation efficiencies were rarely found. The highest DIN and P loads of 23.87 and 4.03 t/day, respectively, were found in Samut Songkhram province. Nutrients were found to contribute to the hypertrophic condition of the lower river and the estuary. The baseline level of chlorophyll a in the upper river was approximately 3.3 microg/L, while levels exceeded 10 microg/L in the estuarine zone. Such chlorophyll a levels were highly significant (p < 0.01) related to DIN and P (with correlation coefficients of 0.44 and 0.37, respectively). In order to maintain river conservation to an acceptable degree, levels of about 20 micromol/L DIN and 1 micromol/L P were suggested as the upper limits. To achieve such levels will require serious consideration with regard to the development of nutrient criteria for water resource conservation management and sustainable utilization purposes.