Mutant of Bordetella pertussis which lacks ability to produce filamentous hemagglutinin.

Mutant cultures that lacked the ability to produce filamentous hemagglutinin were obtained by UV irradiation of Bordetella pertussis strain 18-323. Various biological activities of these mutants were compared with those of the parent culture. It was found that the leukocytosis-promoting, histamine-sensitizing, and mouse-protecting activities of the mutants were similar to those of the parent strain but that the virulence to mice was lower. The results seemed to rule out fimbrial hemagglutinin as a protective antigen when the ability to protect mice was measured by the intracerebral challenge test.