Effects of pure or combined inocula of Escherichia coli and Bacteroides fragilis on the liver and related metabolism.

To test for synergy between a facultative and anaerobic bacterium and the role hepatic hypoxia may have in its development, rats were subjected to intravascular infusion of 10(8) Escherichia coli, 10(9) Bacteroides fragilis, or a combination of both. Acute effects were evaluated by selected 6-hour measurements, including hepatic pO2, and longer range effects by liver cultures and histology in rats surviving 7 days. During the acute period, systemic arterial pressure and pO2 in bacteremic groups did not differ from saline-infused controls. However, hepatic oxygen supply was significantly reduced in E. coli rats and those given the combined bacteria (mean hepatic pO2 less than 10 mm. Hg versus 20.8 mm. Hg in controls). Significant increases of plasma lactate and pulse rate were also recorded. By comparison, hepatic pO2 was not reduced significantly in the B. fragilis rats, and pulse rate was similar to controls. Plasma lactate, however, increases more rapidly than in other groups. Survival rates were 100 per cent in the B. fragilis group, 88 per cent in the E. coli group, and 65 per cent in the combined group. The difference between the latter groups was not significant. Hepatic histology was normal in rats of the B. fragilis group at 7 days postchallenge. In survivors of the E. coli and combined inoculum groups, there was evidence of anoxic damage and occasional foci of neutrophilic infiltration. Liver cultures were more often positive in rats of the combined inoculum group (p less than 0.05), most often for E. coli, than in the other groups. In summary, although the acute effects of E. coli were not changed appreciably by combination with B. fragilis, the higher rate of E. coli liver infection in survivors suggests that its viability was enhanced. The role of hepatic hypoxia in this remains unclear. It is feasible that hypoxic foci provided temporary protection for B. fragilis, enabling the organisms to affect favorably the survival of E. coli.