BORDETELLA

Bordetella organisms are small, Gram-negative coccobacilli which are strict aerobes. The three species of this genus vary in motility and certain biochemical characteristics. The most important species in this genus is B. pertussis, the organism which causes whooping cough. This highly contagious bacterium makes its way into the respiratory tract via inhalation and subsequently binds to and destroys the ciliated epithelial cells of the trachea and bronchi. It does this through the use of several toxins:

• Pertussis toxin- an exotoxin which enters target cells and activates their production of cAMP, a molecule that acts as a second messenger in cell protein synthesis regulation
• Tracheal cytotoxin- causes ciliated epithelial cell destruction
• Hemoagglutinin- a cell surface protein which helps the bacterium bind to the host cell surface

There are about 5000 cases of whooping cough per year in the United States, usually afflicting children less than a year old. A vaccine has reduced the incidence of this disease one hundred fold since its introduction! Despite this extraordinary rate of eradication, controversy exists regarding the safety of the vaccine. Antimicrobial therapy for whooping cough usually consists of erythromycin.

Two other species of Bordetella are also of clinical importance. B. parapertussis is a respiratory pathogen that can cause mild pharyngitis. This bacterium is similar to B. pertussis but lacks some of the toxins which make its sibling so nasty. Biochemical testing can easily differentiate the two species. Bordetella bronchiseptica is usually a cause of pneumonia, otitis media, and other respiratory infections in animals. It is seldom known to be a human pathogen. Its motility makes it easy to distinguish from the other two organisms in this genus.