Cell-associated toxin as a cause of type B botulism in cattle
Haagsma, J.; ter Laak, E.A.
Tijdschrift Voor Diergeneeskunde 103(24): 1317-1326
1978
ISSN/ISBN: 0040-7453 PMID: 364766 Document Number: 135571
Previous studies showed that only a very small amount of type B toxin was present in brewers' grains as free preformed exotoxin. Experiments with two pure cultures of proteolytic type B strains of Cl. botulinum showed that very high concentrations of toxin were present in bacterial pellets obtained after centrifugation, and concentrations increased further following trypsinization. Toxin concentration in the most toxic bacterial pellet was 64 X 106 mouse LD50 per gram. A similar technique was adopted to re-examine brewers' grains used in problem herds, which grains were stored at 4 deg C. Type B toxin in the form of exotoxin then was detected in 56% of the samples, the average concentration of toxin being 18.4 LD50 per gram; however, in 94% of the samples, cell-associated type B toxin was present, the concentration of toxin averaging 154 LD50 per gram. The highest concentration of toxin was one million LD50 per kg of brewers' grains, most of which was present as cell-associated toxin. This means that 6-7 kg of brewers' grains contained a dose of type B toxin lethal for cattle. The MLD for cattle of cell-associated toxin of a bacterial pellet of type B was 7.7 million LD50. Prolonged administration of toxin-free type B spores did not give rise to any symptoms in experimental cattle, and type B did not multiply in the alimentary tract. Therefore there was no evidence to suggest that toxin is produced in vivo. Hence cell-associated toxin is the most important source of toxin in the pathogenesis of botulism type B in cattle.