CHARACTERIZATION OF HEMOLYTIC RTX TOXINS PRODUCED BY AUSTRALIAN ISOLATES OF ACTINOBACILLUS-PLEUROPNEUMONIAE

The haemolytic RTX toxins of 27 isolates of Actinobacillus pleuropneum oniae, representing all serovars that have been isolated in Australia, were characterised. The quantity of protein secreted by these isolate s into the media was not significantly different between serovars, but haemolytic activity was detected only in the unconcentrated supernata nts from cultures of serovar a and 5 isolates. Haemolytic activity in supernatants of serovar 2, 3 and 7 isolates was detected only after th e supernatants were concentrated, On Southern hybridisation blots, gen omic DNA of serovar 1 and 5 isolates contained regions that were simil ar to the cloned structural genes for ApxI (apxIA) and for ApxII (apxI IA). In contrast, genomic DNA of serovar 2, 3 and 7 isolates only cont ained regions similar to, if not identical with, the cloned apxIIA gen e. The haemolytic activity of the culture supernatant depends on the t ype or composition of media and adaptability of the bacteria to in-vit ro cultivation. Low passage cultures of A pleuropneumoniae, which were characterised by waxy colonies, produced significantly weaker haemoly tic activity than A pleuropneumoniae after several passages in vitro.