PRODUCTION OF DIARRHEAL TOXIN BY SELECTED STRAINS OF BACILLUS-CEREUS

The production of diarrheal toxin by six selected strains of Bacillus cereus was monitored during growth at 32 degrees C, a temperature desc ribed as near-optimal for growth and toxin production. Toxic activity was measured in culture filtrates and cellular extracts sampled at thr ee different times during growth. Two alternative methods, a cytotoxic ity test on Chinese hamster ovary (CHO) cells and a commercial immunol ogical test (BCET-RPLA, Oxoid) were used. Toxin titres were in agreeme nt with epidemiological characteristics and toxicity demonstrated: by using other systems in other examinations. A comparison of intra- and extracellular toxicities measured at the exponential and stationary gr owth phases showed that the toxin was essentially secreted during the exponential phase. For several strains, secretion peaked during the pe riod from the middle exponential phase to the beginning of the station ary phase. There was no important overall increase of the toxicity dur ing full and late stationary phase. The level was stable or even lower , thus indicating that diarrheal toxin production during stationary ph ase was small, if any, and that the toxin was unstable under these con ditions. Statistical analysis of toxicities showed that the cytotoxici ty test was correlated with the immunological test (significant at a 1 % level). For routine determinations, a toxicologic laboratory may use any of the two methods, depending On its facilities, the immunologica l test being relatively expensive.