Dermonecrotic activity of Pasteurella multocida strains isolated from pigs in Japanese field.

A total of 241 strains of Pasteurella multocida was isolated from pigs in Japanese field during 1981/82, and was investigated for their dermonecrotic activity for guinea pigs. The strains having the activity were designated as dermonecrotic toxin (DNT) positive (DNT+), and those lacking the activity as DNT negative (DNT-). Of the 241 strains, 62 strains (25.7%) were DNT+ ; 61 were isolated from nasal cavities of a live or dead pigs, and the remaining one was from gross pneumonic lesion. All the DNT+ strains belonged to Carter's serovar D. There were no differences in biologic properties between the DNT+ and DNT- serovar D strains of P. multocida except for dermonecrotic activity. Of all the pigs which showed gross lesions of atrophic rhinitis (AR) and were positive for serovar D strains of P. multocida isolation, 29.5% harbored DNT+ and 26.8% had DNT- strains (P>0.05). Seventy percent of the same population harbored both DNT+ strains of P. multocida and Bordetella bronchiseptica, while 19% yielded only DNT+ strains of P. multocida from nasalcavities (P<0.01). Gross lesions of AR were foundin 12.5% of the vaccinated pigs with commercial AR vaccines, whereas the lesions were found in 92.3% of an unvaccinated pigs. These results suggested that appearence of AR in pigs is due to B. bronchiseptica infection. The DNT+ strains of P. multocida might not be a primary causative agent for swine atrophic rhinitis in Japan.