CHARACTERISTICS OF BACILLUS-CEREUS RELATED TO SAFE FOOD-PRODUCTION

Thirty Bacillus cereus strains, isolated from different sources, were characterized in relation to safe food production. The minimal growth temperatures of the strains varied from less-than-or-equal-to 5-degree s-C to 11-degrees-C. Generation times at 7-degrees-C of strains capabl e of growing at temperatures less-than-or-equal-to 5-degrees-C were ap proximately 8.2 h. The D90-degrees-C-values of spores of strains with a minimal growth temperature of 11-degrees-C determined in phosphate b uffer at pH 7.0 ranged from 4.8 to > 200 min. Strains with the capacit y to grow at temperatures less-than-or-equal-to 9-degrees-C, had a D90 -degrees-C value ranging from 4.6 to 14 min. Addition of either nisin (250 mug/ml) or diacetyl (1500 mug/ml) to the heating menstruem at the single concentrations investigated seemed not to influence the therma l destruction of spores. Germination of spores of almost all strains o ccurred in all three media tested (Brain Heart Infusion, rice extract and milk) even at temperatures below the minimal growth temperature. A ll B. cereus strains tested yielded positive results with a commercial test kit for diarrhoeal enterotoxin. The results indicate that strain s with the capacity to grow at temperatures less-than-or-equal-to 7-de grees-C are not essentially different from those with minimal growth t emperatures of > 10-degrees-C.