Immunoblot of overnight culture supernatants of atypical Shigella B13 strains 5216–70, 3556–77, 3557–77, 3052–94, and 3053–94 incubated overnight at room temperature with purified C1-INH and probed with anti-C1-INH IgG. E. coli O157:H7 EDL933 (EHEC) and S. flexneri 5a M90T were used as positive and negative controls for C1-INH cleavage, respectively.