Pertussis Toxin Plays an Early Role in Respiratory Tract Colonization byBordetella pertussis

Abstract

In this study, we sought to determine whether pertussis toxin (PT), an exotoxin virulence factor produced exclusively by Bordetella pertussis, is important for colonization of the respiratory tract by this pathogen by using a mouse intranasal infection model. By comparing a wild-type Tohama I strain to a mutant strain with an in-frame deletion of the ptx genes encoding PT (⌬PT), we found that the lack of PT confers a significant peak (day 7) colonization defect (1 to 2 log 10 units) over a range of bacterial inoculum doses and that this defect was apparent within 1 to 2 days postinoculation. In mixed-strain infection experiments, the ⌬PT strain showed no competitive disadvantage versus the wild-type strain and colonized at higher levels than in the single-strain infection experiments. To test the hypothesis that soluble PT produced by the wild-type strain in mixed infections enhanced respiratory tract colonization by ⌬PT, we coadministered purified PT with the ⌬PT inoculum and found that colonization was increased to wild-type levels. This effect was not observed when PT was coadministered via a systemic route. Intranasal administration of purified PT up to 14 days prior to inoculation with ⌬PT significantly increased bacterial colonization, but PT administration 1 day after bacterial inoculation did not enhance colonization versus a phosphate-buffered saline control. Analysis of bronchoalveolar lavage fluid samples from mice infected with either wild-type or ⌬PT strains at early times after infection revealed that neutrophil influx to the lungs 48 h postinfection was significantly greater in response to ⌬PT infection, implicating neutrophil chemotaxis as a possible target of PT activity promoting B. pertussis colonization of the respiratory tract.Bordetella pertussis is a gram-negative bacterial pathogen that colonizes the human respiratory tract, leading to a severe paroxysmal coughing disease known as whooping cough. In the absence of a human challenge model of B. pertussis infection, studies of respiratory tract colonization and disease caused by B. pertussis have been limited to animal models, of which the most well established and frequently used is the mouse intranasal inoculation model. In this model, although overt symptomatic disease is not elicited, several characteristics of the human infection are reproduced, such as multiplication and clearance of the bacteria, limitation of infection to the respiratory tract, increased severity of infection in young animals, and various systemic physiological changes (8,25,29,37). Recent studies have shown that this may also be a useful model for the preclinical assessment of acellular pertussis vaccine efficacy (6, 19). However, several aspects of the pathogenic mechanisms employed by B. pertussis and the immune response to this infection remain poorly understood.Pertussis toxin (PT) is a multisubunit exotoxin that is uniquely produced by B. pertussis and is considered one of the important virulence factors of B. pertussis. The holotoxin has an AB 5 structure (33...

Pertussis toxin inhibits neutrophil recruitment to delay antibody-mediated clearance of Bordetella pertussis

“…Although it has many effects on various cell types in vitro, its contributions to B. pertussis infection and pathogenesis have not yet been determined. Recently, Carbonetti et al reported that PTx is required for efficient early colonization by B. pertussis in the lungs of mice (39). Our present data indicate that PTx facilitates B. pertussis colonization by inhibiting early recruitment of neutrophils to the lungs.…”

“…These numbers were indistinguishable from the numbers of wild-type B. pertussis in the lungs at this time point (compare to Figure 4), indicating that PTx is not required for efficient colonization when neutrophils are depleted. These data strongly suggest that PTx enables B. pertussis to colonize the lung by inhibiting neutrophil recruitment, as proposed by Carbonetti et al (39). Immune serum rapidly reduced the number of B. pertussis∆PTx in the lungs of mice treated with PBS on day 3 (P < 0.001) and completely cleared bacteria on day 7 after inoculation (P < 0.001).…”

Lipopolysaccharides from Bordetella pertussis and Bordetella parapertussis Differently Modulate Human Dendritic Cell Functions Resulting in Divergent Prevalence of Th17-Polarized Responses

“…In contrast, severe disease was never observed following B. parapertussis infection (3)(4)(5). Although pertussis toxin is considered to play a critical role for disease occurrence and severity (6,7), it has also been suggested that pertussis toxin may not play a decisive role in causing the typical symptoms of whooping cough (8).…”

Molecular Pathogenesis, Epidemiology, and Clinical Manifestations of Respiratory Infections Due toBordetella pertussisand OtherBordetellaSubspecies

“…pertussis pathogenesis has been studied mainly by using the mouse model of respiratory tract infection (90,91,265,514,778,805). Intranasal and aerosol challenge experiments using B. pertussis and B. parapertussis hu in mice have yielded important insights into the roles of specific virulence factors in determining colonization.…”