Plants and herbal extracts are indispensable for controlling the spread of disease-causing bacteria, including those that infect aquatic organisms used in aquaculture. The use of plant or herbal extract is expected to be safe for aquatic animals and less harmful to the environment, as opposed to conventional therapeutic alternatives such as antibiotics that promote the occurrence of potential antibiotic-resistant bacteria when used improperly. The efficacy of Pandanus tectorius fruit extract in the regulation of Hsp70 expression, pro-phenoloxidase (ProPO), peroxinectin, penaeidin, crustin and transglutaminase, all immune peptides essential for Vibrio tolerance in white leg shrimp, Penaeus vannamei, was investigated in this study, which included the determination of the safety levels of the extract. Tolerance of shrimp against Vibrio parahaemolyticus, a pathogenic bacteria that causes Acute Hepatopancreas Necrosis Disease (AHPND), was assessed on the basis of median lethal dose challenge survival (LD50 = 106 cells/ml). Mortality was not observed 24 h after exposure of 0.5-6 g/L of the fruit extract, indicating that P. tectorius was not toxic to shrimp at these concentrations. A 24-h incubation of 2-6 g/L of the fruit extract increased shrimp tolerance to V. parahaemolyticus, with survival doubled when the maximum dose tested in this study was used. Concomitant with a rise in survival was the increase in immune-related proteins, with Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase increased 10, 11, 11, 0.4, 8 and 13-fold respectively. Histological examination of the hepatopancreas and muscle tissues of Vibrio-infected shrimp primed with P. tectorius extract revealed reduced signs of histopathological degeneration, possibly due to the accumulation of Hsp70, a molecular chaperone crucial to cellular protein folding, tissue repair and immune response of living organisms, including Penaeid shrimp.
Pandanus tectorius leaf extract effect on the White-leg shrimp Penaeus vannamei tolerance against Vibrio parahaemolyticus were investigated in this study. Thirty shrimp post-larvae measured at approximately 1 cm were exposed for 24 h to 0.5, 1, 2, 3, 4, 5 and 6 g/L leaf extract and subsequently observed for survival and immune-related genes expression (Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase), followed by determination of their tolerance and histological tissue profiles upon Vibrio challenge. Survival of shrimps treated with 6 g/L of leaf extract improved by up to 95% to controls. Hsp70, crustin, and prophenoloxidase mRNA levels were observed to be 8.5, 10.4, and 1.5-fold higher, respectively. Histopathological analysis of the hepatopancreas and the muscle tissues revealed major tissue degeneration in Vibrio-challenged shrimps but not in shrimps primed with P. tectorius leaf extract. Of all the dose examined, the best pathogen resistance results were obtained with a 24 h incubation of shrimp in 6 g/L P. tectorius methanolic leaf extract. The tolerance towards V. parahaemolyticus might be associated with the increased regulation of Hsp70, prophenoloxidase and crustin upon exposure to the extract, all immune-related proteins essential for pathogen elimination in Penaeid shrimp. The present study primarily demonstrated that P. tectorius leaf extract is a viable alternative for enhancing P. vannamei post-larvae resistance against V. parahaemolyticus, a major bacterial pathogen in aquaculture.