[PCR and ELISA--in vitro alternatives to the mouse-bioassay for assessing the botulinum-neurotoxin-C1 production potential in environmental samples?].

Botulism is one of the most important bird diseases world-wide and is caused by the intoxication with Botulinum-Neurotoxin-C1 (BoNt-C1), which is produced by toxigenic clostridia under appropriate conditions. Avian botulism leads regularly to large losses among the migrating bird populations breeding and resting at the saltwater pools of the Austrian national park Neusiedler See-Seewinkel. Despite of its ethical dubiousness and its high technical expense the mouse-bioassay is still used as the routine standard method for the detection of BoNt-C1. According to the 3R-concept, in vitro alternative methods for the qualitative detection of BoNt-C1 (immunostick-ELISA) and a corresponding BoNt-C1 gene fragment (nested-PCR) were established. In order to estimate the BoNt-C1 production potential the methods were tested with sediment samples from different saltwater pools subjected to cultivation conditions appropriate for in vitro BoNt-C1-production. With the mouse-bioassay, 52 out of 77 samples were found to have a positive toxin production potential. The immunostick-ELISA showed a similar sensitivity as the mouse-bioassay and exhibited a highly significant positive correlation (r=0.94; p<0.001) with the mouse-bioassay in detecting BoNt-C1. The nested-PCR approach revealed higher numbers of positive BoNt-C1 gene fragment detections as compared to the direct toxin analysis approaches. A weak correlation (r=0.21; p=0.07) with the mouse-bioassay was discernible, no correlation was found with the immunostick-ELISA (r=0.09; p=0.46). Obviously, the PCR approach detected the BoNt-C1 gene fragment in some of the samples where no toxin expression has occurred. Thus it is suggested that the qualitative immunostick-ELISA represents a potential in-vitro alternative to the mouse-bioassay for assessing the BoNt-C1 production potential in environmental samples. In contrast, qualitative BoNt-C1 gene fragment detection via PCR led to an overestimation of the actual toxin production potential.