Full length article Immunostimulation by phospholipopeptide biosurfactant from Staphylococcus hominis in Oreochromis mossambicus Veluchamy Rajeswari, Sekaran Kalaivani Priyadarshini, Viswanathan Saranya, Ponnusamy Suguna, Rajaiah Shenbagarathai * Postgraduate and Research Department of Zoology and Biotechnology, Lady Doak College, Madurai 625002, Tamil Nadu, India article info Article history: Received 26 June 2015 Received in revised form 31 October 2015 Accepted 2 November 2015 Available online 6 November 2015 Keywords: Secondary metabolite Phospholipopeptide biosurfactant Immunostimulant Specific immune response Non-specific immune response Disease resistance abstract The immunostimulatory effect of phospholipopeptide biosurfactant from Staphylococcus hominis (Gen- Bank Accession No: KJ564272) was assessed with Oreochromis mossambicus. The non-specific (serum lysozyme activity, serum antiprotease activity, serum peroxidase activity and serum bactericidal activity), specific (bacterial agglutination assay) immune responses and disease resistance activity against Aero- monas hydrophila were examined. Fish were intraperitonially injected with water soluble secondary metabolite (biosurfactant) of S. hominis at a dose of 2 mg, 20 mg and 200 mg kg 1 body weight. Com- mercial surfactant surfactin (sigma) at 20 mg kg 1 was used as standard and saline as negative control. All the doses of water soluble biosurfactant tested, significantly enhanced the specific, nonspecific im- munity and disease resistance from the day of post administration of phospholipopeptide biosurfactant till the tail of the experimental period. These results clearly indicated that the secondary metabolite isolated from S. hominis stimulates the immunity of finfish thereby could enhance aquaculture production. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Aquaculture is a rapidly growing economic area that contributes nearly half (47.3%) of the world's fish food consumption. Never- theless, one of the main threats to aquaculture is the infectious outbreaks leading to mass mortality in fish [1,2]. A. hydrophila, the motile aeromonads affects a wide variety of freshwater fish species and occasionally marine fish [3]. Improving fish performance in terms of immunity and disease resistance are the major challenges faced by the fish culturists. Though, many measures including routine use of antibiotics have been tried, the excessive and inap- propriate use of antibiotics has resulted in cross resistance against pathogens and accumulation of residues in tissues [4]. The use of organic, inorganic and synthetic compounds such as levamisole [5,6], glucan [7,8], vitamin C and E [9e11], chitin [12], FK-565 (Lac- toyl tetrapeptide) [13], FCA (Freund's Complete Adjuvant) [14,15] as immunostimulant has been increased in recent years. Generally, many microbial products with low molar mass and the group of naturally occurring polymers are surveyed to have an immunoreg- ulatory activity [16]. The components of bacterial cell wall, such as MDP (Muramyl dipeptide), peptidoglucan and LPS (Lipopolysac- charide), attributed to the immunostimulatory effects of aquatic animals [17e19]. However, their role as immunostimulants is controversial for commercial application due to their adverse health effects [20,21]. Microbial secondary metabolites, a protective sub- cellular component has received more attention in disease control. Newaj-Fyzul et al. [22], has demonstrated that feeding rainbow trout with cell-free supernatant of Bacillus subtilis AB1 significantly reduced cumulative mortalities after challenge with Aeromonas sp. Arijo et al. [23], also reported that subcellular components of Vibrio harveyi were successful for the stimulation of immunity and the prevention of V. harveyi infections in rainbow trout, Oncorhynchus mykiss (Walbaum). Hence, screening of new immunostimulants from the secondary metabolites (biosurfactants) of microorganisms could be advantageous to strengthen fish immune system and to reduce the quantity of antibiotics required to control infectious diseases. Many Staphylococcus strains have been reported to produce a number of antimicrobial peptides [24e27]. Staphylococcus hominis MBBL 2e9 produced an antimicrobial peptide, called hominicin which exhibited a high bactericidal activity against methicillin- * Corresponding author. E-mail addresses: shenbagarathai@gmail.com, shenbagarathai@rediffmail.com (R. Shenbagarathai). Contents lists available at ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi http://dx.doi.org/10.1016/j.fsi.2015.11.006 1050-4648/© 2015 Elsevier Ltd. All rights reserved. Fish & Shellfish Immunology 48 (2016) 244e253