The aim of the present study was to extract and characterize bioactive components from separate body organs of Holothuria leucospilota. Preliminary qualitative assessment of the crude extracts was positive for phenols, terpenoids, carbohydrates, flavonoids, saponins, glycosides, cardiac glycosides, steroids, phlobatannins, and tannins in all body organs evaluated. Phenolics were the most abundant group of bioactives accounting for approximately 80%. The extraction solvent mixtures that yielded most compounds evaluated were methanol/acetone (3:1, v:v) and methanol/distilled water (3:1, v:v). In other analyses, GC-MS data revealed diverse metabolic and biologically active compounds, where those in high concentrations included 2-Pentanone, 4-hydroxy-4-methyl- among the ketones; phenol- 2,4-bis(1,1-dimethylethyl)-, a phenol group; and 2-Chlorooctane, a hydrocarbon. Among FA and their methyl/ethyl esters, n-hexadecanoic acid, 5,8,11,14-eicosatetraenoic acid ethyl ester (arachidonic acid), and 5,8,11,14,17-eicosapentaenoic acid methyl ester (EPA) were among the most abundant FAMEs accounting for approximately 50% of the subgroups measured. Data from GC-FID analysis revealed methyl laurate (C12:0), methyl myristate (C14:0), methyl palmitate (C16:0), and methyl stearate (18:0) methyl esters as the most abundant saturated FA, whereas cis-9-oleic methyl ester (C18:1) and methyl linoleate (C18:2) were found as the major monounsaturated FA and PUFA FAMEs, respectively, in the body wall of the species. Taken together, the extraction and characterization of different categories of metabolically and biologically active compounds in various organ extracts of H. leucospilota suggest that the species is potentially a rich source of cholesterol-lowering, antioxidant, antimicrobial, and anticancer agents. These substances are known to benefit human health and assist in disease prevention. These findings justify the use of sea cucumbers in traditional folklore medication and the current interest and attention focused on the species to mine for bioactives in new drugs research.

The link between quorum sensing in Vibrio campbellii and its virulence towards tiger grouper (Epinephelus fuscoguttatus) was investigated using V. campbellii wild type and quorum‐sensing mutants with inactive quorum sensing or constitutively maximal quorum‐sensing activity, and signal molecule synthase mutants. The results showed that wild‐type V. campbellii is pathogenic to grouper larvae, causing more than 50% mortality after 4 days of challenge. Furthermore, the mortality of larvae challenged with the mutant with maximally active quorum sensing was significantly higher than that of larvae challenged with the wild type, whereas a higher survival was observed in the larvae challenged to the mutant with a completely inactive quorum‐sensing system. Grouper larvae challenged with either the signal molecule synthase triple mutant, the harveyi autoinducer‐1 (HAI‐1) synthase mutant and the autoinducer‐2 (AI‐2) synthase mutant showed higher survival than larvae challenged with the wild type. In contrast, larvae challenged with the cholerae autoinducer‐1 (CAI‐1) synthase mutant showed high mortality. This indicates that HAI‐1 and AI‐2, but not CAI‐1, are required for full virulence of V. campbellii towards grouper larvae. Our data suggest that quorum‐sensing inhibition could be an effective strategy to control V. campbellii infections in tiger grouper.

Brown-marbled grouper Epinephelus fuscoguttatus (Forsskål) fingerlings are more vulnerable to diseases than the adult grouper because the fingerlings' adaptive immune system is still in the development stage. The mortality rates are approximately 20 to 70% during outbreaks of vibriosis in aquacultures of grouper fingerlings. Studies were conducted to identify alternative treatments with low impacts on humans, animals and the environment as well as treatments that minimize the use of antibiotics in aquaculture. In this study, we report the first use of surfaceassociated bacteria isolated from marine invertebrates to increase fingerlings' resistance against infections. Twenty-two surface-associated bacteria were isolated from the sea cucumber Stichopus badionotus and were identified with 16S rRNA gene sequencing. Three of the surfaceassociated bacteria had inhibitory activities against pathogenic Vibrio harveyi and V. parahaemolyticus. The fingerlings treated with the surface-associated bacteria Exiguobacterium acetylicum for 12 d prior to the challenge experiment with pathogenic V. harveyi showed significantly higher survival rates and increases in antibody titres compared to the control group. This study illustrats a symbiotic interaction between E. acetylicum and grouper fingerlings. E. acetylicum colonized the scales of grouper fingerlings and enhanced the fish's immune response against the pathogen V. harveyi.

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The aim of this study was to evaluate the effectiveness of the membrane biosynthesis gene disruption in MRSA (methicillin resistant Staphylococcus aureus) using sea cucumber extract (SBE). The disruption of membrane biosynthesis gene also known as multiple peptide resistance gene (mprF), would impair the lysylation of cell membrane phosphatiglycerol and thus reduce antibiotic resistance in MRSA. The membrane permeability assay was done to determine the degree of homology of the SBE treated RNA and the resulting translated protein in MRSA. Bacterial cell permeabilization test was performed to confirm the permeabilization effect of SBE on bacterial cell membranes of the MRSA treatments. The effectiveness of SBE on mprF gene disruption was further confirmed using fluorescence microscopy, modified disc diffusion assay, minimal inhibitory concentration and checkerboard method. Up to 35 % of nucleotide changes at RNA level were detected in methicillin-susceptible S. aureus (MSSA) isolates and less than 10 % in MRSA isolates when treated with SBE, each resulted in alterations in the post-translation protein sequence. The fluorescence assay showed the uptake of fluorescence dye by the bacteria cells treated with SBE, indicating rupturing of the bacterial cell MSSA and MRSA membrane barriers. The in-combination treatments between SBE and classical antibiotics against MRSA resulted in improved inhibitory activities. This study illustrated that the use of SBE caused mprF gene disruption to increase MRSA susceptibility towards AMP substances and classical antibiotics. Thus, disruption of mprF gene can be potential means for reducing antibiotic resistant in MRSA.