Monospecific serum for typing Haemophilus influenzae type b produced by immunization with Escherichia coli strain ‘Easter’

Rabbit and burro antisera produced by injection of an Escherichia coli (075:Kf147:H5) strain Easter reacted only with the type b capsular antigen of whole bacterial extracts of the six types of encapsulated Haemophilus influenzae and strains of H. parainfluenzae, H. hemolyticus and H. aphrophilus. The E. coli antisera had comparable agglutinin, quellung, immunofluorescence and anti type b precipitins in agar gel to H. influenzae type b typing serum. In counter current immunoelectrophoresis used to detect the type b antigen in CSF, serum and other body fluids of patients, the rabbit E. coli antisera had the same specific activity as several preparations of commercially available H. influenzae type b typing reagents. The monospecificity of this E. coli antiserum should avoid false interpretations of serologic tests among H. influenzae types due to cross-rezctions of noncapsular antigens observed at times with H. influenzae type b typing serum. Immunization with this cross-reacting E. coli provides a simple method for preparing typing serum for H. influenzae type b without the hazard of handling potentially pathogenic organisms.