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Vibrio harveyi causes vibriosis in various marine aquaculture fish species, especially when they are young. The infection subsequently leads to significant economic losses for aquaculture farms. Vaccination is recommended to control this disease. This study describes the efficacy of a live attenuated V. harveyi strain MVh_vhs (LAVh) as a vaccine candidate in controlling infection by wild‐type V. harveyi (WTVh) in Lates calcarifer. A total of 240 fingerlings were divided into four groups. Group 1 was not vaccinated and was not challenged, Group 2 was vaccinated with a formalin‐killed V. harveyi (FKVh), Group 3 was vaccinated with the LAVh before challenge and Group 4 was not vaccinated and was challenged. Bath vaccination was employed for one hour before the LAVh distribution was determined in the fish mucus, gill, liver, gut, kidney and spleen. The gills, livers, kidneys and skins were also sampled for gene expression analysis. To challenge the fish, skin abrasion was conducted before the fish were challenged by immersion with WTVh. The results revealed an extensive distribution of the LAVh in the liver and kidneys of the fish in Group 3 for the first 12 hr, resulting in mild lesions compared with Group 1. Similarly, there were significantly (p

Recombinant cell vaccines expressing the OmpK and DnaJ of Vibrio were developed and subsequently, a vaccination efficacy trial was carried out on juvenile seabass (~5 cm; ~20 g). The fish were divided into 5 groups of 50 fish per group, kept in triplicate. Groups 1 and 2 were injected with 107 CFU/mL of the inactivated recombinant cells vaccines, the pET-32/LIC-OmpK and pET-32/LIC-DnaJ, respectively. Group 3 was similarly injected with 107 CFU/mL of inactivated E. coli BL21 (DE3), Group 4 with 107 CFU/mL of formalin killed whole cells V. harveyi, and Group 5 with PBS solution. Serum, mucus, and gut lavage were used to determine the antibody levels before all fish were challenged with V. harveyi, V. alginolyticus, and V. parahemolyticus, respectively on day 15 post-vaccination. There was significant increase in the serum and gut lavage antibody titers in the juvenile seabass vaccinated with r-OmpK vaccine. In addition, there was an up-regulation for TLR2, MyD88, and MHCI genes in the kidney and intestinal tissues of r-OmpK vaccinated fish. At the same time, r-OmpK triggered higher expression level of interleukin IL-10, IL-8, IL-1ß in the spleen, intestine, and kidney compared to r-DnaJ. Overall, r-OmpK and r-DnaJ triggered protection by curbing inflammation and strengthening the adaptive immune response. Vaccinated fish also demonstrated strong cross protection against heterologous of Vibrio isolates, the V. harveyi, V. alginolyticus, and V. parahaemolyticus. The fish vaccinated with r-OmpK protein were completely protected with a relative per cent of survival (RPS) of 90 percent against V. harveyi and 100 percent against V. alginolyticus and V. parahaemolyticus. A semi-quantitative PCR detection of Vibrio spp. from the seawater containing the seabass also revealed that vaccination resulted in reduction of pathogen shedding. In conclusion, our results suggest r-OmpK as a candidate vaccine molecule against multiple Vibrio strain to prevent vibriosis in marine fish.

Seabass (Lates calcarifer) are high value fish occupying a market niche, and is susceptible to infection by pathogenic bacteria such as Vibriosis. In this study the effect of intraperitoneal administration of recombinant outer membrane protein (OMP) of inactivated cells vaccine; r-OmpK on hematological parameters for monitoring fish health and histopathological examination of seabass were investigated. The results revealed that r-OmpK affect some hematological parameters positively in juvenile bass. The r-OmpK vaccinated seabass showed mild histological alterations in the vital organs (spleen, kidney and intestine) when compared to PBS control groups. Further we sought to understand the mechanisms of molecular immunity of L. calcarifer against V. harveyi infection. We carried out an extensive analysis of the transcriptome of L. calcarifer head kidney upon vaccination trial with r-OmpK recombinant cell vaccine and challenged with V. harveyi pathogenic strain VH1. Average reads of 92.74 million and 116.17 million were obtained from head kidney of juvenile L. calcarifer immunized with phosphate buffered saline (PBS) and r-OmpK (10 9 cfu/mL) recombinant cell vaccine, respectively. Also, the analysis revealed that a higher number of genes and pathways were regulated in response to infection with V. harveyi at 48 h post infection compared to the PBS controls. Based on the differential expressed genes (DEGs) around 0.31 % of total unigenes were differentially expressed between the two vaccinated groups. Protein-protein interaction analysis predicts glycolysis pathway, alanine, aspartate and glutamate metabolism pathway, pyruvate metabolism pathway, MAPK signaling pathway, metabolic pathways, insulin signaling pathway and focal adhesion pathway in head kidney of infected fish, which might be useful in understanding biological processes and further studies in the direction of pathways. We reported the novel immune-related signalling pathways, namely complement and coagulation cascades, chemokine signalling pathway, and toll-like receptor signalling pathway having great importance in immunity and anti-inflammation.

A total of 78 lactic acid bacteria (LAB) were isolated from spontaneously fermented camel milk samples and investigated in vitro for their characteristics as potential new probiotic strains. Only nine LAB were active against pathogenic bacteria and imply adhesive properties. The presumed probiotic strains were evaluated for their tolerance to low pH and to 0.3% and 0.5% of bile salts. None of them was able to develop at pH 2 but all showed high resistance to pH 3 compared to the optimal (pH 6.2). Furthermore, all strains showed good bile tolerance. Based on their morphological, physiological and some biochemical characteristics, probiotic strains were assigned to the genus Leuconostoc. Nucleotide sequences of their 16S rRNA showed 94 to 99% similarity to Leuconstoc mesenteroides. The safety results of all nine strains showed the absence of ?. haemolytic activity, gelatinase, DNase, and coagulase. From 14 antibiotics tested, all strains resisted to five only: nalidixic acid, colistin, cefixime, oxacillin and fusidic acid. Overall results indicated that Leuconostoc mesenteroides strains isolated from camel milk could serve as promising probiotic candidates.

The community dynamics of environmental bacteria is dependent on micro-climatic factors such as temperature and water potentials. A shift in any one of these factors can have a major impact on the richness and composition of the microbes in the soil. However, microbial responses towards these climate stressors are poorly characterised. Here, we undertook a microcosm study to assess the effect of temperature and water content on the bacterial community structure in a tropical soil over a four week period. The microcosms were incubated at three different temperatures (25 °C, 30 °C, and 35 °C) and maintained under two different water levels (2 and 5 mL). Using a combination of molecular assessment tools and numerical inference, we showed that short-term variation in both temperature and water content induced significant changes to the soil bacterial community composition. The greatest difference in community structure between treatments was observed in the Week 2 microcosms, but in the Week 4 microcosms, the community structure between treatments became more similar. Compared to temperature, water content exerted a greater effect on the bacterial diversity. Firmicutes was the most abundant phylum in all the analysed samples, and its relative abundance increased with elevation in temperature and water content. Out of six functional genes analysed, the nitrogen fixation gene (nifH) and denitrification gene (nosZ) showed significant correlations to the bacterial community structures.