A novel model of spontaneous lethal gut-derived sepsis originating from the native intestinal microbiota

Author(s):
Sanjiv Hyoju; Jianxin Peng ; Carleen Adriaansens; Emily Salzman; Mara Wiegernick; Alexander Zaborin; Harry Van Goor; Olga Zaborina; John Alverdy

Background:

The gut microbiota are emerging as key members that drive recovery following surgical injury

Hypothesis:

We hypothesize that the combination of a high fat diet and antibiotic exposure create a microbiome capable of causing lethal sepsis in mice following surgical injury.

Methods:

We developed  a novel model in which 7 weeks old C57BL/6 mice are fed a polyunsaturated fatty acid (PUFA) diet typical of a western diet for 6 weeks. Mice were then exposed to 5 days of antibiotics (Abx) consisting of Sub cutaneous cefoxitin and PO clindamycin, as occur during critical illness. Mice were then given water only for 16 hours, similar to NPO after midnight and then subjected to major surgical injury consisting of 30% surgical hepatecotomy. Identically treated chow fed mice served as controls. Mice were followed for the spontaneous development of sepsis and when moribund were sacrified. Blood, liver, spleen, lung, kidney, and cecum were collected for bacterial culture, organ histology and cytokine assays.

Results:

68% of mice treated with PUFA and Abx developed sepsis within 24 hours of surgery and become moribund within 40 hours, whereas only 14% of mice treated with chow and Abx developed lethal sepsis.(N=15/group,p<0.00001). The composition of the cecal microbiome in septic moribund mice in the PUFA+Abx group changed significantly with the emergence of Serratia marcescens and Enterobacter cloacae sp, nearly half of which expressed multi-drug resistance(MDR). Dissemination of these strains into systemic compartments ( liver, spleen, blood) reached 10^6 CFU per gm of tissue( ml of blood). Recovered MDR S.marcescens strains were highly lethal as judged by their killing effect in mouse and Galleria mellonella intraperitoneal models. Phenotypic microarray analysis using Biolog revealed significant metabolic changes and stress/antibiotic resistance in the cecal microbiota.Organ failure was confirmed histologically in the lung, liver and kidney demonstrating hyline membrane formation, tubular vacuolization, glomerular hyper-cellularity and shock liver. Inflammatory biomarkers were elevated including C reactive protein (increased 7 fold), endotoxin (increased 3 fold) and IL-6 (elevated 30 fold) when compared to non-septic mice,p<0.005.

Conclusions:

This novel model demostrates that the combination of a western diet and antibiotics exposure can render surgical patients highly vulnerable to lethal sepsis by  changing the composition and function of commensal bacterial such that highly virulent phenotypes emerge.