NAD-INDEPENDENT ACTINOBACILLUS-PLEUROPNEUMONIAE STRAINS - PRODUCTION OF RTX TOXINS AND INTERACTIONS WITH PORCINE PHAGOCYTES

Actinobacillus pleuropneumoniae RTX toxin (Apr) production by A. pleur opneumoniae biotype 2 (NAD-independent) serotype 2 strains was studied . Western blot analysis of culture supernatants of all biotype 2 strai ns tested revealed the presence of a 103 kDa protein which reacted wit h a monoclonal antibody against ApxILA. This protein was also recogniz ed by sera of pigs infected with a biotype 2-serotype 2 strain. Furthe rmore, antibodies that could neutralize ApxIIA were present in these s era. Proteins corresponding to ApxIA or ApxIIIA were not detected. The effects of a biotype l-serotype 2 and a biotype 2-serotype 2 strain a nd their metabolites on the oxidative activity of porcine pulmonary al veolar macrophages (PAM) and polymorphonuclear cells (PMN) were compar ed using a chemiluminescence (CL) technique. Viable bacteria of both b iotypes stimulated the production of oxygen radicals by phagocytes. CL responses were higher for the biotype 1 than for the biotype 2 strain . After having reached a peak value, the oxidative activity decreased until a total inhibition was achieved. Inactivated washed bacteria had no influence on the oxidative activity of phagocytes. In contrast, he at labile factors in culture supernatants of both biotypes stimulated and inhibited the oxidative activity of PAM in a dose-dependent manner . Dilutions of supernatant up to 1/32 of the biotype 2 strain and up t o 1/512 of the biotype 1 strain were toxic for PAM, while dilutions fr om 1/64 to 1/128 of the biotype 2 strain and from 1/1024 to 1/4096 of the biotype 1 strain stimulated the oxidative activity. To evaluate th e ability of PAM to eliminate low numbers of the biotype l-serotype 2 and the biotype 2-serotype 2 strain, 100 CFU of each strain was incuba ted with 10(5) PAM. The bacterial growth and the viability of PAM were assessed as a function of time. The biotype 1 strain killed PAM more rapidly and multiplication of the bacteria was higher than for the bio type 2 strain.