Efficacy of Mangrove-derived Yeasts as Immunostimulants of Litopenaeus vannamei
(Pacific White Shrimp) Infected with Vibrio parahaemolyticus
Shaira Dawn C. Galacgac1,2*, Frolan A. Aya3 and Gina R. Dedeles1,2
1The Graduate School, University of Santo Tomas, Manila, Philippines
2Pure and Applied Microbiology Laboratory, Research Center for the Natural and Applied Sciences, University of Santo Tomas, Manila, Philippines
3Aquaculture Department, Southeast Asian Fisheries Development Center, Binangonan Freshwater Station, Binangonan, Rizal 1940 Philippines
Litopenaeus vannamei provides a significant universal marketability making it one of the important exchange earners for the Philippines. However, outbreaks of acute hepatopancreatic necrosis disease (AHPND) caused by the Vibrio parahaemolyticus strain resulted in massive mortality and a slump in the shrimp industry. The β-1,3/1,6-glucans of yeasts have been reported to activate the immune system of invertebrates against viral and bacterial infections. In this study, the effectiveness of marine yeasts as immune enhancers of L. vannamei induced with pathogenic V. parahaemolyticus were evaluated. Three (3) marine yeast isolates coded as PASB1, PASB2, and PASB3 isolated from mangrove fallen decaying barks collected at Pasuquin, Ilocos Norte, Philippines were identified phenotypically and molecularly as Candida tropicalis, Candida glabrata, and Pichia kudriavzevii, respectively. Of the three isolates, C. glabrata PASB2 executed the highest growth rate and maximum β-1,3/1,6-glucan yield with 16.04g/100g. The biomass of the selected isolates were incorporated into commercial feeds at 10% concentration. A 1.32×107 CFU/mL dosage of V. parahaemolyticus was used in the challenge tests for the therapeutic and prophylactic setups. In both setups, total hemocyte count (THC) and phenoloxidase activity (PO) revealed that shrimps fed with a diet containing cells of P. kudriavzevii showed a significant increase in immune response compared to other treatment and control groups. This study also demonstrated the significance of the prophylactic approach in preventing AHPND infection. The findings suggest the potential of mangrove-derived P. kudriavzevii as a feed additive and as an effective immune enhancer in L. vannamei against V. parahaemolyticus infection.