Killing of Escherichia coli by human polymorphonuclear leucocytes in the presence of Bacteroides fragilis.

Abstract

The inhibitory effect of Bacteroides fragilis on the in vitro killing of Escherichia coli by polymorphonuclear leucocytes was studied with two pairs of E coli and B fragilis isolated from human wound infections. Both B fragilis strains behaved similarly: they inhibited the killing of one E coli strain, while the killing of the other E coli strain was not affected. The different behaviour of the two E coli strains depended on their need for fresh serum in the killing by the polymorphonuclear leucocytes. The inhibitory effect of the B fragilis strains could be completely accounted for by their effect on complement.