Expression of the dermonecrotic toxin by Bordetella bronchiseptica is not necessary for predisposing to infection with toxigenic Pasteurella multocida

Authors: Brockmeier, Susan; Register, Karen

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2007
Publication Date: 12/15/2007
Citation: Brockmeier, S., Register, K.B. 2007. Expression of the dermonecrotic toxin by Bordetella bronchiseptica is not necessary for predisposing to infection with toxigenic Pasteurella multocida. Veterinary Microbiology. 125(3-4):284-289.

Interpretive Summary: Infection with Bordetella bronchiseptica predisposes pigs to infection with Pasteurella multocida, and coinfection with these agents is often found in cases of progressive atrophic rhinitis, a disease which causes deformed growth of the pig's snout. There are several potential mechanisms by which B. bronchiseptica could predispose to infection with P. multocida. B. bronchiseptica produces a toxin called the dermonecrotic toxin, or DNT, which induces damage to swine nasal tissue and causes pneumonia and could play a role in increased colonization by P. multocida. This experiment was designed to determine whether a strain of B. bronchiseptica which does not produce DNT is still capable of predisposing pigs to infection with P. multocida. Three groups of pigs were initially inoculated with a strain of B. bronchiseptica that produces DNT, a strain of B. bronchiseptica that does not produce DNT, or no B. bronchiseptica. All pigs were then challenged with P. multocida four days later. P. multocida was rarely recovered from pigs initially inoculated with PBS, and no lesions of atrophic rhinitis were present in these pigs. P. multocida was isolated in similar numbers from the pigs initially inoculated with either strain of B. bronchiseptica, and lesions of atrophic rhinitis were seen in pigs from both of these groups. Thus, although the DNT is responsible for much of the pathology seen during infection with B. bronchiseptica by itself, infection with non-DNT producing strains can still predispose to secondary respiratory infections with P. multocida. The results of this experiment are important in considering the development of attenuated intranasal vaccines. Vaccines that may be attenuated due to the lack of DNT production could still contribute to potential secondary infections with other bacteria.

Technical Abstract: This experiment was designed to determine whether a dermonecrotic toxin (DNT) mutant of Bordetella bronchiseptica is still capable of predisposing pigs to infection with toxigenic Pasteurella multocida. Three groups of pigs were initially inoculated with wild type B. bronchiseptica, a DNT mutant of B. bronchiseptica, or PBS. All pigs were then challenged with a toxigenic strain of P. multocida four days later. P. multocida was rarely recovered from pigs initially inoculated with PBS, and no turbinate atrophy was present in these pigs. P. multocida was isolated in similar numbers from the pigs initially inoculated with either wild type or the DNT mutant of B. bronchiseptica, and turbinate atrophy of a similar magnitude was also seen in pigs from both of these groups. Thus, although the DNT is responsible for much of the pathology seen during infection with B. bronchiseptica by itself, infection with non-DNT producing strains can still predispose to secondary respiratory infections with P. multocida.