Relationship between sepsis intensity, Gram-negative bacterial overgrowth and bacterial translocation in rats

Background

Some of the enteric microbiota role is linked to the gut immune system, the angiogenic mechanism and colonization resistance, and its disruption has been correlated to local disease and aggravation of a systemic inflammatory state such as in sepsis and critical illness. Herein we examined the role of diverse sepsis intensities on aerobic and anaerobic facultative Gram-negative microbiota of the small bowel (SB) and large bowel (LB) and subsequent bacterial translocation (BT) potentials in rats.

Methods

Wistar rats (± 200 g) were submitted to varying degrees of monobacterial sepsis (S-7, S-8 and S-9 groups, with 10⁷, 10⁸ and 10⁹ colony-forming units/ml/100 g body weight of Escherichia coli R6 intravenously, respectively) and samples of the duodenum, jejunum, ileum, cecum, feces, mesenteric lymph nodes (MLN), liver and spleen were harvested at 6, 12 and 24 hours post sepsis and cultured in MacConkey agar medium (n = 6/period/group). Control groups were sham with saline injection and naïve without any procedure (n = 6/period/group).

Results

The Gram-negative colonization rise within the SB occurred from the proximal to distal compartments and significant overgrowth onset was seen from 6 hours in the SB and 12 hours in the LB in the sepsis groups, suggesting that LB overgrowth was probably due to SB overgrowth. With severe sepsis (S-8, S-9), the overgrowth was more pronounced and remained for a longer period at the ileum and cecum, but at the duodenum and jejunum the peak growth seen in the 6 to 12 hours period returned to normal level at 24 hours. The maximum overgrowth index comparisons between naïve, S-8 and S-9 were (log₁₀): 0.0 versus 2.8 versus 4.7 (duodenum), 2.5 versus 4.2 versus 6.0 (jejunum), 4.0 versus 7.4 versus 7.5 (ileum), and 5.1 versus 8.0 versus 7.8 (cecum), respectively. Spontaneous BT to the MLN occurred only following sepsis (50% at S-8, 5.6% at both S-7 and S-9) and was 100% E. coli. Not only E. coli but all other Gram-negatives were overgrown after sepsis stimulus. S-7 and minor trauma (sham) provoked a transient overgrowth but in lesser intensity and endurance.

Conclusion

Acute sepsis states induced a significant and transient SB and LB Gram-negative microbiota overgrowth directly proportional to the severity of sepsis. The BT event was dependent on both the sepsis degree and overgrowth factors.