Antimicrobial peptide gene expression in tiger shrimp, Penaeus monodon in response to gram-positive bacterial probionts and white spot virus challenge

Prophylactic approach is gaining more and more importance in aquaculture, because of the ever increasing outbreak of viral diseases and the regulations on the use of chemotherapeutants. Use of probiotics has been widely accepted in aquaculture for the prevention and control of diseases. But the exact mode of action of probiotic bacteria still remains enigmatic. The use of antimicrobial peptides (AMPs) as a therapeutic tool has been among the most promising avenues investigated, to date, because of their unique mode of action and for addressing antibiotic resistance. The present work aims at studying the effect of three probiotic preparations viz. Bacillus MCCB101, Micrococcus MCCB104 and combination of Bacillus MCCB101 + Micrococcus MCCB104 on the expression of three major families of AMPs in Penaeus monodon pre- and post-challenge white spot virus (WSV), employing semi-quantitative RT-PCR. The study showed that the administration of probiotic bacteria, up-regulated the AMP genes considerably both pre- and post-challenge WSV. Probionts administered individually and in combination were found to alter the level of expression of AMP genes. Bacillus MCCB101 was found to be the best among the three probiotics studied in terms of AMP gene expression and survival rate. Hence, tissue-wise expression profile of AMP genes on administration of probiotic Bacillus was also studied. Gill and intestine were found to support maximum up-regulation of AMP genes. The work accentuates the application of probiotic bacteria as an excellent mode of immunostimulation and also proves that enhanced production of AMPs could be a possible mode of action of probiotic bacteria.