Bacterial translocation consequential to intestinal bacterial overgrowth provokes aggravation of mortality by sepsis

Increasing evidence from experimental and clinical studies has eluded to the 'intestinal hypothesis of sepsis', which is based on bacterial or endotoxin translocation from the intestinal lumen to the extra-intestinal sites, thus generating an exacerbated inflammatory response leading to the aggravation of the pre-existing sepsis state or to the onset of sepsis. Nevertheless, growing acceptance of the 'intestinal hypothesis' was mainly triggered by indirect rather than concrete scientific evidence. In this study we examined the role of the association of bacterial translocation with varying severity of sepsis states, monitoring mortality and recovery of translocated bacteria in several host compartments using a rat model of bacterial translocation (BT) and sepsis (S).

Methods

BT groups: midline laparotomy was performed on Wistar rats under ketamine + hydroxychloral anesthesia (4:1). Rats were inoculated with 10 ml 10⁷/10¹⁰ cfu/ml Escherichia coli R-6 (n = 20/group) by oroduodenal catheterization, which was confined to the small intestine by ligation of both the duodenum and ileum. S groups: inoculation of 10⁷/10⁹/10¹⁰ cfu/ml/100 g body weight Enterobacter cloacae 89 into the portal vein (n = 20/group). BT + S groups: 10¹⁰ BT + 10⁷/10⁹ S (n = 20/group). From 10 animals of each group, samples of mesenteric lymph node, liver, spleen and blood were collected 2 hours post inoculation and cultured in MacConkey agar medium. The remaining animals in each group were observed for mortality for 30 days (n = 10/group).

Results

BT-10⁷/10¹⁰ did not cause death and only 10¹⁰ inoculum promoted BT (mean = 1.8 × 10⁵ cfu/g tissue). S-10⁷ was not lethal, but promoted a transient bacteremia state, S-10⁹ was LD₈₅ within 25 hours, and S-10¹⁰ showed LD₁₀₀ within 5 hours. Bacterial recovery from these groups/g tissue were, at the most, 10⁴ cfu at S-10⁷, 10⁷ cfu at S-10⁹ and 10⁸ cfu at S-10¹⁰. BT-10¹⁰ in combination with S-10⁷ showed significantly increased mortality (LD₅₀ within 32 hours) as compared with BT-10¹⁰ (LD₀) and S-10 (LD₀) alone (P < 0.05), and the mortality rate was statistically similar to the severe sepsis group (S-10⁹). In addition, the association of BT-10¹⁰ + S-10⁹ also provoked a significant increase in mortality (LD₁₀₀ within 13 hours) as compared with BT-10¹⁰ (LD₀) and S-10⁹ (LD₈₅ within 25 hours) in terms of length of time to cause mortality (P < 0.05). Besides, sepsis in combination with BT showed a decreased rate of translocation in all groups as compared with the BT group alone. Overall data demonstrated significant deleterious synergistic effects of BT in combination with all states of sepsis, suggesting that translocation of bacteria through the gut-associated lymphoid system (GALT) favors the activation of the host systemic inflammatory response, even though the total quantification of internalized bacteria in the host compartments did not change at all by the addition of the BT process. Therefore, BT appears to provoke an exacerbated inflammatory state due to the bacterial challenge to the GALT during their traffic through mesenteric lymphatic tissue rather than the quantitative physical presence of the bacteria in the systemic compartment, therefore suggesting a distinctive GALTrelated host inflammatory response associated with the BT phenomena.