Bacteriostatic effect of flavonoids isolated from leaves of Psidium guajava on fish pathogens

The antimicrobial activity against fish bacterial pathogens of flavonoids (morin, morin-3-O-lyxoside, morin-3-O-arabinoside, quercetin, and quercetin-3-O-arabinoside) isolated from the leaves of Psidium guajava was evaluated. The flavonoids were shown to have bacteriostatic effect on all of the tested bacteria.     

Effect of <Emphasis Type="Italic">Cratoxylum formosum</Emphasis> on innate immune response and disease resistance against <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> in tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

The effect of aqueous extract of Cratoxylum formosum on innate immune response and disease resistance in tilapia Oreochromis niloticus was investigated. The fish were fed diets containing 0% (control), 0.5% (diet 1), 1% (diet 2), and 1.5% (diet 3) of C. formosum aqueous extract for 30 days. At the end of the experimental period, parameters of innate immune response including phagocytosis of blood leukocytes, lysozyme activity in plasma, and respiratory bust activity were examined. Feeding the fish with diet 2 and diet 3 for 20 days enhanced phagocytic activity and for 30 days stimulated lysozyme and respiratory burst activities. Diet 1 increased the phagocytic activity at 30 days, but did not affect the other measured parameters. All parameters were not significantly changed (P > 0.05) in the control group throughout the experiment. Following 30 days of feeding, fish were infected with S. agalactiae. The cumulative mortalities of bacterial-infected tilapia that were fed diet 1, diet 2, and diet 3 were 56, 12, and 10%, respectively, compared with 85% in the control group. These results indicate that the aqueous extract of C. formosum may elevate the innate immune response and enhance disease resistance in tilapia.     

Molecular characterization and expression of the Prostaglandin reductase 1 gene and protein during ovarian development of the giant tiger shrimp Penaeus monodon

Prostaglandin reductase 1 (PTGR1; also called NADP⁺-dependent leukotriene B4 12-hydroxydehydrogenase, LTB4DH) is the key enzyme responsible for biological inactivation of prostaglandins and related eicosanoids. In this study, the full-length cDNA of PTGR1 in the giant tiger shrimp (Penaeus monodon) was characterized. PmPTGR1 was 2405 bp in length with an ORF of 1035 bp encoding a polypeptide of 344 amino acids. Interestingly, its 3′ UTR contained the nucleotide sequence (825 bp) that significantly matched positions 3–277 (with 4 amino acid variants) of the deduced P. monodon peritrophin2 protein. PmPTGR1 was more preferentially expressed in ovaries than testes of P. monodon broodstock. In intact broodstock, PmPTGR1 was up-regulated in early cortical rod (stage III) ovaries (P < 0.05) and comparably expressed afterwards (P > 0.05). In eyestalk-ablated broodstock, PmPTGR1 was temporally lower in early cortical rod compared to previtellogenic (I) and vitellogenic (II) ovaries (P < 0.05) and returned to the previous level in mature (IV) ovaries (P < 0.05). More importantly, the relative expression level of PmPTGR1 in each ovarian stage in eyestalk-ablated females was lower than that in intact P. monodon broodstock (P < 0.05). This strongly suggested that eyestalk ablation potentially affects the expression of PmPTGR1 allowing the stimulating effects of prostaglandins and related eicosanoids on vitellogenesis and ovarian maturation of P. monodon. The level of ovarian PmPTGR1 protein seemed to increase during ovarian development in intact broodstock but slightly reduced in mature ovaries in eyestalk-ablated broodstock. Results suggested the possible contribution of PmPTGR1 in ovarian development of P. monodon.     

Potential of cinnamon (<Emphasis Type="Italic">Cinnamomum verum</Emphasis>) oil to control <Emphasis Type="Italic">Streptococcus iniae</Emphasis> infection in tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

In this study, four essential oils—cinnamon oil, leech lime oil, lemongrass oil, and turmeric oil—were examined for their antimicrobial activities against Streptococcus iniae, a bacterium that is pathogenic in fish, in which it causes streptococcosis. Cinnamon oil was the most potent antimicrobial agent among these oils, with a minimal inhibitory concentration (MIC) of 40 μg/ml. By using gas chromatography–mass spectrometry (GC–MS), it was found that the major components of cinnamon oil were cinnamaldehyde (90.24), limonene (2.42%), cinnamyl acetate (2.03%), linalool (1.16%), and α-terpineol (0.87%). Of these compounds, only cinnamaldehyde exhibited antimicrobial activity against S. iniae, with an MIC of 20 μg/ml. In an in vivo trial, no mortality was apparent in fish fed on fish diets supplemented with 0.4% (w/w) of cinnamon oil and with 0.1% (w/w) of oxytetracycline 5 days prior to infection with S. iniae. These results indicate that cinnamon oil had a protective effect on experimental S. iniae infection in tilapia, and thus has the potential to replace the antibiotics used to control this disease.     

Potential of Chinese chive oil as a natural antimicrobial for controlling <Emphasis Type="Italic">Flavobacterium columnare</Emphasis> infection in Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

Chinese chive Allium tuberosum oil was studied for its diallyl sulfide content and its antimicrobial activity against Flavobacterium columnare in fish both in vitro and. The oil was found to have a very low concentration of diallyl monosulfide relative to the other diallyl sulfides (diallyl disulfide, diallyl trisulfide, and diallyl tetrasulfide) identified. In the in vitro study, the Chinese chive oil had a bacteriocidal effect on all tested strains of F. columnare, with varied minimal inhibitory concentrations. The median lethal dose (LD₅₀) of FC4 for Nile tilapia Oreochromis niloticus was determined to be 3.72 × 10³ CFU/fish. In the in vivo trial, no mortality was observed in fish fed fish diets supplemented with 800 mg/kg Chinese chive oil and 100 mg/kg of oxytetracycline hydrochloride 5 days prior to infection with F. columnare strain 4 at a LD₅₀. These results indicate that Chinese chive oil has the potential to replace antibiotics for controlling fish disease caused by F. columnare.