The pathological effect of the Bordetella dermonecrotic toxin in mice

The effect of dermonecrotic toxin (DNT) expression of Bordetella bronchisep tica was studied in mice by comparing the pathology induced by a wild type strain with that induced by an isogenic DNT- strain in which part of the st ructural gene has been replaced by an antibiotic resistance cassette. While extracts of strain B58 proved toxic in intravenously inoculated mice, simi lar extracts from strain B58GP had lost toxic activity. The parent (B58) an d the mutant (B58GP) strains of B. bronchiseptica each possessed comparable virulence for mice. These findings confirmed that DNT production was succe ssfully abolished in strain B58GP while other virulence characteristics req uired for pathogenicity in mice remained intact, at a comparable level to t he parent strain. Turbinate atrophy was observed in mice infected with the DNT+ strain, but not in those infected with the DNT- strain. This indicates that DNT is the cause of turbinate atrophy in the mice and not other facto rs produced by phase I strains of B. bronchiseptica. B. bronchiseptica DNT showed a lienotoxic effect (lymphocyte depletion and a reduction in the int ensity of extramedullar haemocytopoieis) that is considered to adversely al ter the immune function of the host animal. In mice infected with strain B5 8GP, catarrhal pneumonia with characteristic lympho-histiocytic peribronchi al and perivascular infiltration was noticed. In mice infected with strain B58, large necrotic areas were seen surrounded by an inflammatory reaction. The DNT appears to directly damage lung tissues, at least in mice. DNT pro duction seems to enhance the establishment of B. bronchiseptica in the lung s, presumably by reducing the local resistance and causing severe local dam age to the lung tissues.