Complement-mediated bacteriolysis after binding of specific antibodies to drug-resistant Pseudomonas aeruginosa: morphological changes observed by using a field emission scanning electron microscope

A bactericidal mechanism mediated by human serum was investigated by a field emission scanning electron microscope and a strain of drug-resistant Pseudomonas aeruginosa. When the bacteria were treated with meropenem, a carbapenem antibiotic, spheroplasts and bulges (spheroidization) appeared after 1–3 h. When 40% serum was added to the bacteria, the bacteria agglutinated within 2 min and then lysed after 5–30 min. Immunoelectron micrographic analyses showed dispositions of complement component C9 molecules on the cell surface of lysed bacteria by the serum treatment that might suggest formation of a membrane attack complex. Immunoglobulin G (IgG) depletion from the serum diminished the lytic activity and adding human intravenous immunoglobulin (IVIG) restored it, suggesting that lysis was induced by specific IgG binding to the bacteria. IVIG may help patients with less IgG against bacteria to overcome severe infection.