Effect of the presence of black pigmented Bacteroides of differing pathogenicity on the phagocytosis of Escherichia coli by rat polymorphonuclear leucocytes.

An investigation was made of the ability of rat polymorphonuclear leucocytes (PMNLs) to phagocytose Escherichia coli in the presence of two species of black pigmented Bacteroides (B. melaninogenicus and B. intermedius). When both the bacteria were opsonized together in the presence of normal rat serum, B. melaninogenicus and B. intermedius impaired the phagocytosis of E. coli significantly. However, the phagocytosis of these black pigmented Bacteroides remained unaffected in the presence of E. coli. The inhibition of phagocytosis was seen only after the initial first hour of incubation. The inhibition of phagocytosis of E. coli in the presence of B. intermedius was more than in the presence of B. melaninogenicus. The above observation confirms the important role played by black pigmented Bacteroides in experimental mixed infections with E. coli as observed by us earlier.