UTILIZAÇÃO DO QUORUM SENSING NA EXPRESSÃO DE ANTÍGENOS VACINAIS EM Escherichia coli Enterotoxigênica

Abstract

One of the most important sanitary problems that cause economic losses in swine industry is the diarrhea caused by Enterotoxigenic Escherichia coli (ETEC). It is the main infectious cause of mortality for animals in suckling and post-weaning periods. Their primary factors of pathogenicity are the fimbriae, which bond the bacteria to specific receptors of the enterocytes. This causes a succession of events, brought about by the enterotoxins, the stable toxins (ST) and heat-labile toxins (LT), leading to diarrhea. Another important structure is the flagellum, which has an important role in cell stimulation to produce pro-inflammatory cytokines through the interaction with Toll-like receptors (TLR5), signaling cell recruitment and activation, thus increasing local inflammation as well as antigen presentation to lymphocytes. Quorum Sensing is a signaling system among bacteria that uses substances denominated autoinducers (AI). When the auto-inducers reach a certain concentration, due to an increase of cell density, there is an activation of transcriptional factors, which regulate the gene expression. The catecholamines (adrenaline and noradrenalin), produced by nervous cells, use the auto-inducer type 3 (AI-3) pathway. These have a significant role in gene expression as they stimulate the growth and the expression of virulence factors of the Escherichia coli. The goal of the present study was to produce experimental vaccines containing total cultures of ETEC cultivated in different induction conditions, mediated by the conditioned media (mc) so as to study the expression of vaccine antigens. Different concentrations of mc were used, with the 50% of conditioned media added with 500 μM of adrenaline having the major initial growth and antigen expression. In the motility assay, a sixteen-fold increase was observed in comparison to the control. By the ELISA, hemoagglutination, hemoagglutination inhibition and Dot Blot techniques, a higher expression of fimbriae (F4) was observed, whereas by Dot Blot, ELISA and RT-PCR techniques an increase of LT expression was observed. Based on this data a bacterin was prepared using 50% of mc and 500 μM of adrenaline, with Al(OH)3 as an adjuvant. Five weeks old Swiss female mice were vaccinated twice with 250 μL subcutaneously on days 0 and 8 14. The vaccine immune response was evaluated by ELISA and hemoagglutination inhibition. The mc bacterin vaccinated group respond with a seroconversion significantly higher that the control group. These results suggest that the presence of mc with adrenaline is capable of activating the expression of important vaccine antigens, therefore making bacterin more efficient.