ABSTRACTChanges in serological activity of enterotoxin A were measured by an immuno‐diffusion method. The reducing sugars xylose, lactose, glucose, maltose and fructose did not react with enterotoxin so as to reduce titer under various conditions of concentration, pH, temperature and time but all of these sugars exhibited an enterotoxin protective effect when systems were heated at 60°C. Sodium propionate, sodium benzoate and sodium nitrite at various concentrations did not alter enterotoxin titer when systems were incubated up to 9 days at 21 or 37°C. Sodium sulfite at a solution concentration of 1000 ppm decreased titers under specific conditions that suggest weak complex formation with the enterotoxin. Luxuriant growth of bacteria belonging to the generaBacillus, Micrococcus, Brevibacterium, Aeudomonas, Proteus, Escherichia, Enterobacter, and yeasts of the generaCandidaandSaccharomyces, in several media containing enterotoxin A did not significantly alter exterotoxin titer. Titer was substantially reduced by several species of lactic acid bacteria includingL. acidophilus, L. helveticus, L. plantatum, L. mesenteroides, Strep. thermophilus, Strep. faecalisvar.liquefaciens, Strep. lactisandP:pentosaceusin MRS broth and by five of the above species in APT broth. Reductions in titer were not simply due to decreases in pH by these organisms. Studies on heat inactivated enterotoxm revealed partial reactivation in phosphate‐buffered saline incubated at 30 and 37°C for 72 hr but not at several other conditions of lower temperature and shorte
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