Emergence of bactericidal and opsonizing antibody to Vibrio vulnificus following bacterial infection

Virulent isolates of Vibrio vulnificus resist the bactericidal and opsonizing effects of normal human serum, in contrast to environmental isolates, which are highly serum susceptible. Immune responses to bacteremic V. vulnificus infections in human subjects have not been characterized. Serum from a patient who survived sepsis caused by V. vulnificus had substantial bactericidal and opsonizing immunoglobulin G (IgG) for his own bloodstream isolate. Killing was mediated by the classical complement pathway, whereas opsonization was effected by either the classical or the alternative pathway. IgG that reacted strongly with 55-, 58-, and 68-kilodalton outer membrane proteins was present in the patient's convalescent-phase serum but was absent from normal human serum. These findings suggest that humoral immunity to V. vulnificus, mediated by bactericidal and opsonizing antibody, emerges during infection and may be due, in part, to IgG directed against identifiable outer membrane proteins.