The pathogenic synergy of aerobic and anaerobic bacteria has long been recognised in a variety of infections e.g. in intra-abdominal sepsis, pleuro-pulmonary infections and brain abscesses. Despite recent advances in management, such infections remain a serious problem.
Animal studies have confirmed the pathogenic synergy of aerobic and anaerobic bacteria. The precise mechanisms for this have not yet been fully elucidated, but one group of investigators has proposed the hypothesis that anaerobic bacteria inhibit phagocytosis of aerobic bacteria by human leucocytes (Ingham et al., 1977).
To acquire a fuller understanding of the pathogenesis of these mixed infections this hypothesis was tested by studying phagocytosis as measured by killing and chemiluminescence of aerobic bacteria in the presence of anaerobic bacteria.
Our in vitro experiments showed that anaerobic bacteria interfere with the phagocytosis and killing of aerobic bacteria. However, this inhibitory effect was not a property of all Bacteroides species. Killing of aerobic bacteria was inhibited by culture filtrates of B. gingivalis strain W83. Washed bacterial cells of strain W83 did not show an inhibitory effect. The inhibitory factor was heat-stable and had a molecular weight of less than 3500.
Chemiluminescence (CL) was used to determine whether a burst in oxidative metabolism occurs when PMN leucocytes encounter aerobes and anaerobes. CL consistently occurred when PMN leucocytes encountered aerobes. However, no chemiluminescence was observed when human PMN leucocytes were challenged with culture filtrates of Bacteroides species alone or in combination with aerobic bacteria.