SEROLOGY AND CHARACTERIZATION OF TOXIGENIC BACILLUS-CEREUS

None of the isolates of Bacillus cereus from vomiting-type outbreaks h ydrolysed starch. Spores from such strains were heat-resistant (5 min at 105-degrees-C). The serotypes from outbreaks with vomiting included H-1, H-5 and H-8. In contrast, the isolates from outbreaks with diarr hoea hydrolysed starch, their spores were not heat-resistant (30 min a t 100-degrees-C) and the serotypes differed from one outbreak to anoth er. Seven phages were isolated, purified and used for typing isolates. The H-1 isolates from outbreaks with vomiting were typed into 6 phage patterns with this set of phages. Enterotoxin from B. cereus (BCET) w as purified by physicochemical procedures or by immunoaffinity chromat ography with a monoclonal antibody against BCET. Minute concentrations of BCET (1-2 mug L-1) were detected within 18 h by the RPLA test. The isolates from outbreaks with diarrhoea produced high concentrations o f BCET, 1,6-3,2 mg L-1, but most isolates from outbreaks with vomiting did not produce BCET, less than 10 mug L-1. The emetic toxin was not satisfactorily characterized. The vacuolation factor with high activit y was produced in cooked rice medium and in skim-milk. The isolates fr om outbreaks with vomiting, especially of serotype H-1, produced that factor in titres of 20-160 in cooked rice medium (the titre correspond ing to the greatest dilution factor for which vacuolation could be obs erved in HEp-2 cells), whereas none of those from outbreaks with diarr hoea did so. A partially purified vacuolation factor was stable, resis ting various treatments (e.g. heating, change in pH and treatment with enzyme). Monkeys given 30 000-36 000 arbitrary units (a unit correspo nding to 1 mL of supernatant with titre 1 or 1 muL of supernatant with titre 1000) each vomited in 3,5-7 h. Thus the vacuolation factor is p robably the emetic toxin itself. Prevalence of B. cereus in samples of raw milk was not high, number fraction of samples 0,048-0,086. By con trast, it was in commercial defatted powdered milk, 0,436, in which co unts of B. cereus were 10(4)-10(7) L-1 or 10-(4)-10(7) kg-1. Growth, c urd formation and toxin production by B. cereus were examined in paste urized milk at 10, 20 and 30-degrees-C. At 20-degrees-C, milk produced BCET, 2-8 mug L-1, in 12-18 h and the vacuolation factor to a titre o f 4-8 in 24-36 h.