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Abstract: Lipopolysaccharides (LPS), the outer membrane of the Gram-negative bacteria, are reported to stimulate the immunity of different vertebrates including fish. However, their potency and spectrum of actions often differ among different bacteria. In this study, effect of crude LPS, derived from three species of smooth Gram-negative bacterial fish pathogens viz. Edwardsiella tarda, Escherichia coli, and Pseudomonas fluorescens, on certain innate immune parameters of Indian major carp, Labeo rohita was studied. L. rohita yearlings, when injected intraperitoneally with crude LPS extracted from these bacteria showed little variations in different innate immune parameters. Furthermore, LPS injected fish were protected against a virulent E. tarda challenge. Although, no significant difference (p >0.05) in most of the immune parameters were found with LPS of different bacteria, the E. coli LPS injected fish elucidated high resistivity during challenge study. Hence, there could be some variations in LPS with respect to the bacterial type which needs to be further explored. [Copyright &y& Elsevier]

Abstract: Bacterial lipopolysaccharides (LPS), also termed endotoxins, considered to be a major virulence factor, are responsible for the lethal effects and clinical manifestations of diseases in humans and animals. Higher animals are extremely sensitive to endotoxin even at low doses but lower vertebrates like fish are often resistant to endotoxic shock. Toll-like receptor (TLR)-4 is mainly involved in the activation of the immune system by LPS through the specific recognition of its endotoxin (Lipid A) moiety. Although several Toll-like receptors are present in fish, those molecules specifically involved in TLR-4 mediated endotoxin recognition have not been fully established in different fish species. Despite this, LPS has the potency to express cytokines, acute-phase proteins and also exerts immunological, pathological, physiological, immuno-endocrinological and neuro-immunological effects in several fish species. The immunostimulating effects of endotoxin by triggering various immune parameters such as T and B lymphocytes, macrophages, and complement systems have been established in teleosts. This article reviews the multiple biological effects of endotoxin which will further strengthen the knowledge among researchers on various aspects of endotoxin in lower vertebrates, particularly in the piscine system. [Copyright &y& Elsevier]

Abstract: Endotoxin, a lipopolysaccharide component of outer cell wall membrane of the Gram-negative bacteria is a factor responsible for a number of biological effects including immunostimulatory activities in different animal species including fish. In this study, L. rohita yearlings of weight ranging from 80 to 100g were injected intraperitoneally with 0.5, 1, 2, 5, 10 and 20EU/fish dose of endotoxin to find out its effect on the immunity. The L. rohita yearlings were found to resist the endotoxin dose up to 20EU/fish and at the lower doses, i.e., at 1 and 2EU/fish; it acted as an immune potentiator. Different serum and immune parameters like protein, globulin, lysozyme, respiratory burst activity, myeloperoxidase activity, natural agglutination titre were found to be significantly high (p <0.01) at a dose of 1EU/fish. While at 10 and 20EU/fish, most of these parameters were lower thereby indicating the immuno-suppressive nature of the endotoxin at these higher doses. [Copyright &y& Elsevier]

Abstract: Aeromonas hydrophila is a Gram-negative bacteria associated with many disease conditions of aquatic animals. Two rough attenuated variants were derived from two smooth virulent types of this bacterium by continuous passage separately in laboratory over a period of 8 years in brain–heart infusion agar. These variants were checked to be rough lipopolysaccharides (LPS) types and attenuated since they neither produced any disease nor mortality in the injected fishes. The immunogenic potential of these variants remained unaltered as compared to parent smooth types and fish immunized with these variants resisted the infection and mortality upon cross challenge. Because of their intact immunogenic potential and loss of virulence, they may be used as candidates for fish immunization. [Copyright &y& Elsevier]