KILLER FACTOR INTERFERENCE IN MIXED OPPORTUNISTIC YEAST CULTURES

The interaction of the killer yeast Pichia anomala UP 25F with the kil ler toxin-sensitive clinical isolate Candida albicans UCSC 10S and its natural toxin-resistant mutant derivative C. albicans UCSC 10R were s tudied under various conditions. A differential inhibition was shown t o occur in vitro at pH and temperature values, which are not encounter ed in vivo, only by using preformed killer toxin, since antagonism due to yeast growth proved to be predominant on the killer effect. Under adverse growth conditions, the P. anomala killer yeast proved to be ab le to produce an anatoxin antigenically related to the active or heat inactivated killer toxin. These findings suggest that killer toxins ma y not function as potential virulence factors in the competition betwe en the opportunistic killer yeast P. anomala and sensitive microorgani sms for colonization in the course of natural human infections.