Previous bacterial translocation challenge enhances peripheral blood bacterial clearance in the subsequent sepsis

Introduction

A bacterial translocation (BT) event has been strongly related to the pathogenesis of sepsis as well as to the sepsis progression to the state of multiple organ failure, and increasing scientific findings have pointed out the beneficial role of BT by building a gut immune defense repertoire. In a previous study, we have demonstrated that a previous BT challenge reduces significantly the translocation index at the second BT challenge with the same bacterial strain. Thereby, in this study we sought to evaluate the effect of previous BT challenge on experimentally induced sepsis, examining the bacterial clearance index from the systemic blood circulation, in order to evaluate its influence on the host's immunological defense response.

Methods

Adult female Wistar rats (200–250 g) were submitted to BT (5 ml Escherichia coli R-6 10¹⁰ CFU/ml/100 g body weight confined to the small intestine for 2 hours) and after 2 weeks were submitted to semi-lethal and lethal sepsis induction (inoculation of 10⁹ or 10¹⁰ CFU/ml/100 g body weight E. coli R-6 into the portal vein, respectively), and serial hemocultures were monitored at 0, 15, 30, 60 and 120 min. The BT control group received saline only (n = 8/group). In the other group (n = 6), we evaluated the BT capacity of inducing anti-E. coli R6 O-antigen antibody production after 14 days.

Results

Animals submitted to previous BT in combination with semi-lethal sepsis demonstrated a significantly faster bacterial clearance index when compared with animals that were not submitted to previous BT. Also, specific antibody against E. coli R6 was detected in 4/6 animals submitted to BT only 14 days before, suggesting that BT challenge can induce a specific immune response and play a protective role against further second bacterial challenge. However, when animals were submitted to a high concentration of bacteria (lethal sepsis, DL₁₀₀), previous BT challenge could not play its beneficial role.

Conclusion

BT is able to build a host's specific immune response, although it is dependent on the sepsis severity.