Pathogen-specific immune modulation in Nile tilapia: A comparative transcriptomic study of infections by Nocardia asteroides and Providencia vermicola.

Bacterial diseases have a significant impact on the Nile tilapia (Oreochromis niloticus) industry in Mexico. Understanding the mechanisms of host-pathogen interactions enables the design of effective control and diagnostic strategies to reduce losses during cultivation. This work aimed to analyze the transcriptome of Nile tilapia infected with emerging bacterial pathogens. Three experimental groups were established: two infected with Nocardia asteroides or Providencia vermicola, and a healthy control (non-infected group). Results showed that both infections caused mortality and signs of disease, most notably the group infected with N. asteroides registering the highest mortality rate. The transcriptomic analysis revealed that both N. asteroides and P. vermicola modulated pathways related to amino acid metabolism, cell adhesion molecule expression, innate immune response, antigen processing and presentation, and neuropeptide signaling. Remarkably, N. asteroides infection significantly modulated immune pathways involved in cytokine signaling, phagocytosis, and complement activation. Comparative analysis revealed that N. asteroides downregulates cell-mediated adaptive immunity and upregulates cytokines associated with the anti-inflammatory response, as well as cell proliferation and differentiation. Meanwhile, P. vermicola induced hormonal and neurotransmitter signaling pathways, including genes related to antimicrobial peptides and tumor necrosis factor receptors, while energy production-related metabolic pathways were downregulated.