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Molecular characterization of two Bordetella bronchiseptica strains isolated from children with coughs
P Stefanelli1, P Mastrantonio, S Z Hausman
1Department of Bacteriology and Medical Mycology, Istituto Superiore di Sanitf1a, Rome, Italy.
Insights
Variant Bordetella bronchiseptica strains were identified in infants with cough. These strains, though not initially producing pertussis toxin (PT), contained the genetic information for PT production, suggesting potential human pathogenicity.
Area of Science:
- Bacteriology
- Immunology
- Vaccinology
Background:
- Surveillance for new acellular pertussis vaccines identified unusual bacterial isolates.
- Two isolates from infants with cough exhibited characteristics of both Bordetella bronchiseptica and Bordetella parapertussis.
Purpose of the Study:
- To investigate the potential of these Bordetella isolates to produce pertussis toxin (PT).
- To determine if the isolates contained the genetic basis for PT production and if it could be activated.
Main Methods:
- Biochemical identification and serological agglutination tests.
- Analysis of the ptx gene region and promoter activity.
- Insertion of an active promoter to test for PT production.
Main Results:
- Isolates were identified as Bordetella bronchiseptica but cross-agglutinated with Bordetella parapertussis antisera.
- Neither isolate produced PT under standard conditions, but both possessed partial ptx gene sequences.
- Activation of the ptx region resulted in the production of biologically active PT.
Conclusions:
- The findings suggest the existence of variant Bordetella bronchiseptica strains.
- These variant strains may possess the genetic capability to produce functional pertussis toxin.
- Such strains could potentially cause significant human illness.
Abstract:
During a surveillance program associated with the Italian clinical trial for the evaluation of new acellular pertussis vaccines, two bacterial isolates were obtained in cultures of samples from immunocompetent infants who had episodes of cough. Both clinical isolates were identified as Bordetella bronchiseptica by biochemical criteria, although both strains agglutinated with antisera specific for Bordetella parapertussis, suggesting that the strains exhibited some characteristics of both B. bronchiseptica and B. parapertussis. Both children from whom these strains were isolated exhibited an increase in serum antibody titer to pertussis toxin (PT), a protein that is produced by Bordetella pertussis but that is not thought to be produced by B. bronchiseptica. We therefore examined whether the clinical isolates were capable of producing PT. Neither strain produced PT under laboratory conditions, although both strains appeared to contain a portion of the ptx region that encodes the structural subunits of PT. In order to determine whether the ptx genes may encode functional proteins, we inserted an active promoter directly upstream of the ptx region of one of these strains. Biologically active PT was produced, suggesting that this strain contains the genetic information necessary to encode an active PT molecule. Sequence analysis of the ptx promoter region of both strains indicated that, while they shared homology with the B. bronchiseptica ATCC 4617 sequence, they contained certain sequence motifs that are characteristic of B. parapertussis and certain motifs that are characteristic of B. pertussis. Taken together, these findings suggest that variant strains of B. bronchiseptica exist and might be capable of causing significant illness in humans.