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Two main probiotics (Lactobacillus plantarum and L. delbrueckii ssp. bulguricus) were isolated from the intestine of Barbus grypus and their characteristics were determined using biochemical, molecular and probiotical tests (bacterial antagonistic effects and lack of pathogenicity to fish). The effect that these lactic acid bacteria (LAB) had on the immune response of juveniles B. grypus and their resistance to Aeromonas hydrophila when fed as a dietary supplement was examined in the present study. The fish were randomly divided into four groups of 120 fish and were fed with diet containing 5 9 10 7 CFU g -1 of each isolated LAB, Lactobacillus casei PTCC 1608 or a control diet with no bacteria for 60 days, after which half of the fish from each group were challenged with A. hydrophila, while the remaining fish were fed with the control diets for a further 15 days. Various immune parameters were examined at 30 and 60 days post-feeding (dpf), and also 15 days after stopping feeding the probiotic. The results showed that dietary administration of L. plantarum significantly increased serum lysozyme, complement and respiratory burst activities in the serum of B. grypus by 30 dpf. The highest bactericidal activity was observed in the serum of fish fed the diet containing L. delbruecki ssp. bulguricus. Fish fed with diet containing L. delbruecki and L. plantarum had significantly higher survival rates than those fed the control diet after challenge with A. hydrophila. The results suggest that dietary supplementation with L. plantarum and L. delbrueck, isolated from B. grypus, can stimulate selected immune parameters in B. grypus infected with A.

Quorum quenching (QQ), the enzymatic degradation of N-acyl homoserine lactones (AHLs), has been suggested as a promising strategy to control bacterial diseases. In this study, 10 AHL-degrading bacteria isolated from the intestine of barramundi were identified by 16S rDNA sequencing. They were able to degrade both short and long-chain AHLs associated with several pathogenic Vibrio species (spp.) in fish, including N-[(RS)-3-Hydroxybutyryl]-l-homoserine lactone (3-oh-C4-HSL), N-Hexanoyl-l-homoserine lactone (C6-HSL), N-(β-Ketocaproyl)-l-homoserine lactone (3-oxo-C6-HSL), N-(3-Oxodecanoyl)-l-homoserine lactone (3-oxo-C10-HSL), N-(3-Oxotetradecanoyl)-l-homoserine lactone (3-oxo-C14-HSL). Five QQ isolates (QQIs) belonging to the Bacillus and Shewanella genera, showed high capacity to degrade both synthetic AHLs as well as natural AHLs produced by Vibrio harveyi and Vibrio alginolyticus using the well-diffusion method and thin-layer chromatography (TLC). The genes responsible for QQ activity, including aiiA, ytnP, and aaC were also detected. Analysis of the amino acid sequences from the predicted lactonases revealed the presence of the conserved motif HxHxDH. The selected isolates were further characterized in terms of their probiotic potentials in vitro. Based on our scoring system, Bacillus thuringiensis QQ1 and Bacillus cereus QQ2 exhibited suitable probiotic characteristics, including the production of spore and exoenzymes, resistance to bile salts and pH, high potential to adhere on mucus, appropriate growth abilities, safety to barramundi, and sensitivity to antibiotics. These isolates, therefore, constitute new QQ probiotics that could be used to control vibriosis in Lates calcalifer.

Pasteurella multocida is responsible for numerous economically relevant diseases in domestic animals worldwide. In cattle and buffaloes the organism is associated with hemorrhagic septicemia (hS) and bovine respiratory disease (BrD). the aim of this study was to investigate twelve virulence associated genes in 22 strains of P. multocida isolated from slaughtered cattle and buffaloes. the most frequently detected genes among bovine isolates were ptfA, nanH, exbBD-tonB and oma87; whereas hgbB and toxA genes occurred less frequently. Some of the adhesions, sialidases, iron acquisition and protectin proteins occurred at considerably (P<0.05) higher frequencies in bovine isolates. the prevalence of oma87, exbBD-tonB and hgbA genes from buffaloes was significant (P<0.05), whereas the prevalence of hgbB, ompH, pfhA and toxA genes was much lower. all tested strains of P. multocida contained the sodC gene and only 22.7% of them had sodA. By using the virulence gene profiles, 12 and 21 different gene combinations were identified among the strains isolated from cattle and buffaloes, respectively, of which Profile C1 was the most common, with all strains possessing toxa. Our results indicate the presence of virulence factors (VFs) in P. multocida strains isolated from the tested cattle and buffaloes. the occurrence of these factors in apparently healthy animals could possibly indicate early infection or a contained infection which did not lead to disease. Moreover, differences in the frequency of these factors may indicate variations in the pathogenicity of the organism.