Central nervous system (CNS) infections continue to be an important cause of morbidity and mortality, and microbial invasion of the blood-brain barrier (BBB) is considered a prerequisite for CNS infections, which contribute to behavioural abnormalities and disease pathogenesis. Based on this information, the aim of this study was to evaluate whether Pseudomonas aeruginosa causes disruption of the BBB, and to investigate the involvement of cerebral myeloperoxidase (MPO) activity in this process in experimentally infected silver catfish. The permeability of the BBB to Evans blue dye increased in the infected animals on days three and six post-infection (PI) compared to the control group. Moreover, cerebral MPO activity and reactive oxygen species (ROS) levels also increased in the infected animals on days three and six PI compared to the control group. Based on this evidence, we concluded that P. aaeruginosa causes a disruption of the BBB, which may contribute to disease pathogenesis in the CNS. Moreover, the increase in cerebral MPO activity and ROS levels may be considered a pathway involved in BBB breakdown, allowing the passage of bacteria to the CNS.

Several studies have been demonstrated that phosphotransfer network, through the adenylate kinase (AK) and pyruvate kinase (PK) activities, allows for new perspectives leading to understanding of disease conditions associated with disturbances in energy metabolism, metabolic monitoring and signalling. In this sense, the aim of this study was to evaluate whether experimental infection by Aeromonas caviae alters hepatic AK and PK activities of silver catfish Rhamdia quelen. Hepatic AK and PK activities decreased in infected animals compared to uninfected animals, as well as the hepatic adenosine triphosphate (ATP) levels. Also, a severe hepatic damage was observed in the infected animals due to the presence of dilation and congestion of vessels, degeneration of hepatocytes and loss of liver parenchyma architecture and sinusoidal structure. Therefore, we have demonstrated, for the first time, that experimental infection by A. caviae inhibits key enzymes linked to the communication between sites of ATP generation and ATP utilization. Moreover, the absence of a reciprocal compensatory mechanism between these enzymes contributes directly to hepatic damage and for a severe energetic imbalance, which may contribute to disease pathophysiology.

Objective: Investigate the influence of the antimicrobial peptides P34 and nisin on the expression of genes associated with components of the cell surface of Listeria monocytogenes and Listeria seeligeri.Methods: Antimicrobial activity was determined by addition of peptide P34 and nisin (12.5 µg/ml) onto Brain Heart Infusion agar (BHI) plates previously inoculated with indicator strains (L. monocytogenes ATCC 7644 or L. seeligeri AC 82/4) after incubation for 24 h at 37 °C or 240 h at 4 °C. Ribonucleic acid (RNA) was directly extracted from bacterial colonies at the border of the inhibition zones, and the expression levels of genes Dalanine-D-alanyl carrier protein ligase (dltA), putative phospholipid lysinylation (Imo 1695) and EIIAB Man Results: A non-significant increase in the levels of transcription of genes dltA, Imo1695 and mptA was observed for L. monocytogenes treated with peptide P34 or nisin. Both peptides caused a similar decrease in dltA gene expression in L. seeligeri. The expression of gene Imo1695 significantly decreased (about 2000-fold) after treatment with the peptide P34 at 37 °C, while at 4 °C a reduction of 12-fold and 5-fold was detected for P34 and nisin, respectively. A significant decrease in mptA gene expression was observed by exposition to peptide P34 (31.872-fold) and nisin (16.047-fold) for 24 h at 37 °C.of mannose-specific PTS (mptA) were determined using real-time PCR. Conclusion:The results suggest that both peptide P34 and nisin influence the expression of genes related with the cell-surface/cell-membrane structure of L. seeligeri and in lesser extent L. monocytogenes.