Susceptibility of the liver and biliary tract to anaerobic infection in extrahepatic biliary tract obstruction. III. Possible synergistic effect between anaerobic and aerobic bacteria. An experimental study in rabbits.

The pathogenicity of single anaerobic, single aerobic, and mixed anaerobic and aerobic bacterial inocula was studied in 3 groups of 12 rabbits with biliary tract obstruction. B. fragilis, ss. fragilis and E. coli serotype 01: K1: H7 were used. The investigation was made 7 days after bacterial inoculation and included bacteriological studies of the liver and bile as well as studies of liver function and morphology of the liver and biliary tract. Inoculation of 10(5)-10(6) E. coli did not cause biliary tract infection, liver abscesses or death. Inoculation of 10(9) B. fragilis caused biliary tract infection in 83% and liver abscesses in 17% of the animals inoculated, without any mortality. Combined inoculation with B. fragilis and E. coli in reduced doses significantly increased mortality (42%) and frequency of liver abscesses in surviving animals (86%). All abscesses, however, yielded pure culture of B. fragilis only. 84% of the animals inoculated with B. fragilis alone or with B. fragilis in combination with E. coli developed biliary tract infection with B. fragilis, the bile yielding from 10(7)-10(9) B. fragilis per ml, gallbladder bile yielding significantly higher bacterial counts than common duct bile. E coli was never recovered from bile in surviving animals but from both bile and blood in animals not surviving the experimental period.