Meningitis caused by Aeromonas hydrophila in Oreochromis niloticus: Proteomics and druggability of virulence factors.

Meningitis caused by Gram-negative bacteria is a serious public health problem, causing morbidity and mortality in both children and adults. Here, we propose a novel experimental model using Nile tilapia (Oreochromis niloticus) to study neuroinflammation. The fish were infected with Aeromonas hydrophila, and the course of infection was monitored in the peripheral blood. Septicemia was obvious in the blood, while in the brain tissue, infection of the meninges was present. The histopathological examination showed suppurative meningitis, and the cellular immune response in the brain tissue during infection was mediated by microglia. These cells were morphologically characterized and phenotyped by MHC class II markers and CD68. The increased production of TNF-α, IL-1ß and iNOS supported the infiltration of these cells during the neuroinflammatory process. In the proteomic analysis of A. hydrophila isolated from brain tissue, we found chemotactic and transport proteins, proteolytic enzymes and enzymes associated with the dismutation of nitric oxide (NO), as well as motor proteins and those responsible for cell division. After characterizing the most abundant proteins during the course of infection, we investigated the druggability index of these proteins and identified promising peptide sequences as molecular targets that are similar among bacteria. Thus, these findings deepened the understanding of the pathophysiology of meningitis caused by A. hydrophila. Moreover, through the proteomics analysis, important mechanisms and pathways used by the pathogen to subvert the host response were revealed, providing insights for the development of novel antibiotics and vaccines.

Proteomic analysis capsule synthesis and redox mechanisms in the intracellular survival of group B Streptococcus in fish microglia.

Group B Streptococcus (GBS) causes meningitis in neonates and Nile tilapia (Oreochromis niloticus). The molecular mechanisms regulating the intracellular survival of this pathogen in the host cell are complex and crucial for the progression of infection. Thus, we propose the use of GBS-infected Nile tilapia microglia as an in vitro model system simulating infection caused by homologous bacteria in humans. We used this model to evaluate the phagocytic activity, as well as the functional aspects of the capsular proteins A, B, C, and D and the major redox enzymes, and the synergistic role of mechanisms/proteins involved in blocking phagocytic process. We observed that in the intracellular phase, GBS showed enhanced synthesis of the polysaccharide capsule and used superoxide dismutase, thioredoxin, NADH oxidase, and alkyl hydroperoxide reductase to scavenge reactive oxygen species and reactive nitrogen species produced by the host cell. Furthermore, although these virulence mechanisms were effective during the initial hours of infection, they were not able to subvert microglial responses, which partially neutralized the infection. Altogether, our findings provided important information regarding the intracellular survival mechanisms of GBS and perspectives for the production of new drugs and vaccines, through the druggability analysis of specific proteins. In conclusion, tilapia microglia serve as a potent in vitro experimental model for the study of meningitis.