Genetic Studies of the Molecular Basis of Whooping Cough

The etiologic agent of whooping cough, Bordetella pertussis, synthesizes several biochemically and biologically active factors believed to contribute to the disease process. They include filamentous hemagglutinin (FHA), pertussis toxin (PTX), adenylate cyclase toxin (AC), and hemolysin (HLY). We have used a genetic approach to evaluate the contribution of these factors to the virulence of B. pertussis. A series of B. pertussis mutants prepared by transposon Tn5 insertion mutagenesis were characterized and determined to be specifically deficient in the elaboration of these factors. The wild type strain and the mutants were tested for their ability to produce a lethal infection in the classical infant mouse intranasal infection model. The dose of organisms required to cause lethal infection in 50% of the animals (LD50) for the wild type strain was 2 X 10(3) bacteria. A mutant deficient in production of the proposed adherence factor, FHA, was equivalent in virulence to the wild type strain (BP353, LD50 = 8 X 10(3)). In contrast, mutants deficient in production of PTX alone (BP357, LD50 = 5 X 10(6)), AC and HLY (BP348, LD50 greater than 3 X 10(7)), or all known toxins and virulence factors (BP347, LD50 greater than 3 X 10(7)) were severely impaired in their ability to cause a lethal infection. Our data indicate the hemolysin and adenylate cyclase as well as pertussis toxin are important virulence factors and provide the basis for a working model of the molecular basis of the disease caused by Bordetella pertussis.