Complement‐mediated bactericidal activity of human milk to a serum‐susceptible strain of E. coli 0111

There has been a lot of controversy concerning the physiological significance of the complement system in human breast‐milk. This is mainly due to the observation that human milk contains predominantly non‐inflammatory and many anti‐inflammatory factors, while simultaneously protecting the infant against a wide range of infectious and other diseases. The present study was carried out to assess the contribution of the complement system to the bactericidal activity of the human colostrum and early lactational milk. Using a serum‐sensitive strain of Escherichia coli, different fractions of human breast‐milk were assessed for their ability to kill the bacteria, with and without inactivation of their complement components, in comparison to another strain of the bacteria species. Deposition of activated C3 fragments on the killed bacteria, using an established ELISA technique, was demonstrated, further proving that the human milk complement could be activated in vitro. The bactericidal activities of human milk were almost completely abolished by complement heat inactivation at 56 °C or by the addition of EDTA.