A rapid micro-method for the study of antibody-mediated killing of bacteria, with specific application to infection of sheep with Pasteurella haemolytica.

A micro-titration plate bactericidal assay was developed to measure complement-dependent antibody-mediated killing of Pasteurella haemolytica. Sera and lung washings from specific pathogen-free (SPF) lambs convalescent from a challenge with live, virulent P. haemolytica were bactericidal in the presence of complement. Similar samples from naive SPF lambs had no such activity. Purified IgG derived from a convalescent lamb serum was as bactericidal as the whole serum. Absorption of convalescent serum with lipopolysaccharide from P. haemolytica abolished bactericidal activity, suggesting that this antigen may be a target for antibody in the bactericidal complex.