Serological Assay of Culture Filtrates for Staphylococcus Enterotoxin.

color from ammonia was produced by an additional 5 min of incubation at 37 C. All strains of Proteus, except those of P. inconstans, generated detectable amounts of ammonia (Table 1). None of the Escherichia organisms was urease-positive. These findings were identical with those yielded by the urease technique of Stuart et al. The sensitivity of the Berthelot color reaction permits detection of urease activity of singlecolony isolates within minutes. Moreover, the proposed technique is rapid and reliable, thereby facilitating identification of Enterobacteriaceae. It is noteworthy that the Berthelot color reaction may be advantageous in demonstrating urease activity of organisms which hydrolyze urea much more slowly than does Proteus. For example, ammonia was detected from single-colony isolates of Aerobacter aerogenes after as little as 15 min of incubation in aqueous urea prior to color development. Application of the Berthelot color reaction to members of the paracolon group is currently under investigation in our laboratories.