Review of the biology of Bordetella pertussis

Bordetella pertussis produces a complex array of adhesins, aggressins and t oxins that are presumed to be important in the colonisation of its human ho st and in ensuring its survival and propagation. The organism also has high ly sophisticated mechanisms for regulating virulence factor expression, in response to environmental signals or by reversible mutations. Despite the r apidly increasing knowledge of these aspects of the biology of B. pertussis , our understanding of the pathogenesis of whooping cough is still far from clear. In defining the role of individual factors, reliance has to be plac ed on in vitro assays or animal models of the human infection, particularly in the mouse, where different conditions may prevail. Some clues to pathog enic mechanisms may be provided by considering other bordetellae, especiall y B. parapertussis, B. bronchiseptica and B. avium, their similar, but not identical, range of virulence factors and the common features of the diseas es caused by these species in their respective hosts. The bordetellae are u sually defined as obligate, non-invasive parasites of the respiratory tract s of warm-blooded animals, including birds, with a predilection for the res piratory ciliated epithelium. This definition has been challenged by a numb er of recent observations. For example, the ability of Bordetella sop. to r egulate virulence factor expression in response to external signals strongl y suggests that they have alternative habitats where such regulation would be an advantage. These habitats may be intracellular, since it has been sho wn that B. pertussis, B, parapertussis and B. bronchiseptica can invade and survive within host cells, or they may be in other sites within the same o r different hosts. Recent DNA fingerprinting studies of B. pertussis have r evealed hitherto unsuspected heterogeneity amongst isolates which could be reflected in antigenic differences between strains. Some of these new persp ectives on Bordetella pathogenicity may have implications for pertussis vac cine development. (C) 1999 The International Association for Biologicals.