Whooping cough bacteria (Bordetella pertussis), computer illustration. B. pertussis are gram-negative, aerobic, non-motile, coccobacillus bacteria. They are spread by coughing and by nasal drops. The incubation period is 7-14 days. A vaccine is available for this bacterial pathogen. Pertussis vaccine is part of the DTaP (diphtheria, tetanus, acellular pertussis) immunization. B. pertussis also produces a lymphocytosis-promoting factor, which causes a decrease in the entry of lymphocytes into lymph nodes. This can lead to a condition known as lymphocytosis.