Expression profiles of four Nile Tilapia innate immune genes during early stages of Aeromonas veronii infection.

OBJECTIVE: During Egypt's hot summer season, Aeromonas veronii infection causes catastrophic mortality on Nile Tilapia Oreochromis niloticus farms. Egypt is ranked first in aquaculture production in Africa, sixth in aquaculture production worldwide, and third in global tilapia production. This study aimed to investigate, at the molecular level, the early innate immune responses of Nile Tilapia to experimental A. veronii infection. METHODS: The relative gene expression, co-expression clustering, and correlation of four selected immune genes were studied by quantitative real-time polymerase chain reaction in four organs (spleen, liver, gills, and intestine) for up to 72 h after a waterborne A. veronii challenge. The four genes studied were nucleotide-binding oligomerization domain 1 (NOD1), lipopolysaccharide-binding protein (LBP), natural killer-lysin (NKL), and interleukin-1 beta (IL-1ß). RESULT: The four genes showed significant transcriptional upregulation in response to infection. At 72 h postchallenge, the highest NOD1 and IL-1ß expression levels were recorded in the spleen, whereas the highest LBP and NKL expression levels were found in the gills. Pairwise distances of the data points and the hierarchical relationship showed that NOD1 clustered with IL-1ß, whereas LBP clustered with NKL; both genes within each cluster showed a significant positive expression correlation. Tissue clustering indicated that the responses of only the gill and intestine exhibited a significant positive correlation. CONCLUSION: The results suggest that NOD1, LBP, NKL, and IL-1ß genes play pivotal roles in the early innate immune response of Nile Tilapia to A. veronii infection, and the postinfection expression profile trends of these genes imply tissue-/organ-specific responses and synchronized co-regulation.

Comparison of Vietnamese and US isolates of Edwardsiella ictaluri.

We compared Edwardsiella ictaluri from striped catfish in Vietnam with US channel catfish isolates. Biochemical analyses and sequencing of the 16S rRNA gene confirmed that the Vietnamese isolates were E. ictaluri. Comparison using rep-PCR fingerprinting demonstrated no significant differences between the isolates, but plasmid analysis indicated that the Vietnamese isolates grouped into 4 plasmid profiles, each different from the typical pEI1 and pEI2 plasmid profile found in the US isolates. Sequencing plasmids representative of the 4 profiles indicated that all contained derivatives of the E. ictaluri plasmid pEI1, whereas only 1 contained a plasmid derivative of the E. ictaluri plasmid pEI2. The pEI2 encoded type III secretion effector, EseI, and its chaperone, EscD, were found to be present on the chromosome in isolates lacking a pEI2 derivative. In addition, 1 isolate carried a 5023 bp plasmid that does not have homology to either pEI1 or pEI2. Furthermore, Vietnamese isolates were PCR positive for the type III and type VI secretion system genes esrC and evpC, respectively, and the urease enzyme, but were PCR-negative for the putative type IV secretion system gene virD4. A monoclonal antibody against the lipopolysaccharide of E. ictaluri ATCC 33202 did not react with the Asian isolates or with the more recent US isolates. Antibiotic resistance patterns were variable and did not correlate to the presence of any particular plasmid profile. Finally, the Vietnamese isolates were avirulent and had a significantly reduced capacity for intracellular replication within head-kidney-derived channel catfish macrophages.

In-vitro inhibition of spring viremia of carp virus replication by RNA interference targeting the RNA-dependent RNA polymerase gene.

Spring viremia of carp, a fatal viral disease, is caused by the spring viremia of carp virus (SVCV) and can result in up to 70% mortalities in common carps and significant economic losses in several other cyprinid aquaculture. The present study aimed to investigate the possible control of SVCV replication in Epithelioma papulosum cyprini (EPC) cells using the RNA interference technology targeting the RNA-dependent RNA polymerase (L) gene of the SVCV that is essential for its replication. Three stealth small interfering RNA (siRNA) sequences were designed to target three different regions on the SVCV-L gene. The specific siRNAs designed were investigated individually or in combinations to inhibit the SVCV-L gene expression and the virus replication. Results showed that the most effective siRNA sequence was the siRNA-602 that specifically reduced the SVCV replication by two logs as indicated by the virus titration and quantitative real-time PCR. Results, also, showed that the minimum effective concentration of siRNA-602 was 20 nM when used to transfect the EPC cells before the virus inoculation. Results of this study clearly indicate that targeting the SVCV-L gene by RNAi can reduce the SVCV replication in vitro, that may lead to the control of SVCV in fish.