Conversion of Bordetella pertussis to Bordetella parapertussis.

The epidemiological and drug susceptibility data on whooping cough suggested a possibility that Bordetella pertussis converts in some way to Bordetella parapertussis. To prove this, B. pertussis strain 75 was treated with N-methyl-N'-nitro-N-nitrosoguanidine and a mutant resistant to staphcillin v and eight mutants resistant to trimethoprim were isolated. The staphcillin V-resistant mutant of B. pertussis agreed with all of the criteria of B. parapertussis and the trimethoprim-resistant mutants also agreed with many of these criteria. Thus, a hypothesis is presented that B. parapertussis is a mutant of B. pertussis which appeared in nature probably by a selective pressure of antibiotics.