Non-gastrointestinal Bacillus cereus infections: an analysis of exotoxin production by strains isolated over a two-year period.

Isolates of Bacillus cereus from 118 cases, and two maternity unit outbreaks, of non-gastrointestinal infection were grouped on the basis of their estimated probable involvement in the infections from which they were isolated: (i) high probability--48 strains; (ii) intermediate--16 strains; (iii) low--7 strains; (iv) very low ("irrelevant")--49 strains. Rabbit skin test, haemolysin and phospholipase assays were used to determine exotoxin activities of strains within each group. The results suggest a significant relation between the virulence of an isolate as reflected in the degree to which it appeared responsible for the signs and symptoms of an infection, and its toxigenicity in the skin test. This is attributed to the ability of B cereus strains to synthesise, in varying degrees, a necrotic enterotoxin, possibly in conjunction with the primary haemolysin (cereolysin). The cases analysed in this study support the contention that B cereus, when isolated from an infection, may not be an inconsequential contaminant and should not be too readily dismissed as such.