Identification and expression profiles of multiple genes in Nile tilapia in response to bacterial infections

To understand the molecular mechanisms involved in response of Nile tilapia (Oreochromis niloticus) to bacterial infection, suppression subtractive cDNA hybridization technique was used to identify upregulated genes in the posterior kidney of Nile tilapia at 6 h post infection with Aeromonas hydrophila. A total of 31 unique expressed sequence tags (ESTs) were identified from 192 clones of the subtractive cDNA library. Quantitative PCR revealed that nine of the 31 ESTs were significantly (p < 0.05) upregulated in Nile tilapia at 6 h post infection with A. hydrophila at an injection dose of 105 CFU per fish (∼20% mortality). Of the nine upregulated genes, four were also significantly (p < 0.05) induced in Nile tilapia at 6 h post infection with A. hydrophila at an injection dose of 106 CFU per fish (∼60% mortality). Of the four genes induced by A. hydrophila at both injection doses, three were also significantly (p < 0.05) upregulated in Nile tilapia at 6 h post infection with Streptococcus iniae at doses of 106 and at 105 CFU per fish (∼70% and ∼30% mortality, respectively). The three genes induced by both bacteria included EST 2A05 (similar to adenylate kinase domain containing protein 1), EST 2G11 (unknown protein, shared similarity with Salmo salar IgH locus B genomic sequence with e value of 0.02), and EST 2H04 (unknown protein). Significant upregulation of these genes in Nile tilapia following bacterial infections suggested that they might play important roles in host response to infections of A. hydrophila and S. iniae.