This work deals with the production of antibodies against each component of the Non-hemolytic enterotoxin (Nhe) of Bacillus cereus and their use for qualitative and quantitative analyses of the enterotoxin profiles of 100 B. cereus strains.

To facilitate the detection of this toxin, consisting of the subunits NheA, NheB, and NheC, a complete set of high-affinity antibodies against each of the three components was established and characterized. A rabbit antiserum specific for the C-terminal part of NheC was produced using a respective synthetic peptide coupled to a protein carrier for immunization. Using purified B. cereus exoprotein preparations as immunogens, one monoclonal antibody against NheA and several antibodies against NheB were obtained. No cross-reactivity with other proteins produced by different strains of B. cereus was observed. Antibodies against the NheB component were able to neutralize the cytotoxic activity (up to 98 %) of Nhe.

To evaluate the expression of HBL and Nhe, a set of 100 B. cereus strains was examined. Molecular biological characterization showed that 42 % of the strains harboured the genes for HBL and 99 % for Nhe. The production of all HBL and Nhe components was analyzed using specific antibodies and, in culture supernatants, detectable levels of HBL and Nhe were found for 100 % of hbl-positive and 96 % of nhe-positive strains. The concentrations of the HBL–L2 and NheB component ranged from 0.02 to 5.6 µg/ml and from 0.03 to 14.2 µg/ml, respectively. Comparison of the amount of NheB and HBL-L2 produced by food poisoning and food/environmental strains revealed that the median values for all food poisoning strains were higher than for the food/environmental isolates.

The data presented in this work provide evidence that specific and quantitative determination of the enterotoxins is necessary to evaluate the enterotoxic potential of B. cereus. In particular, the level of Nhe seems to explain most of the cytotoxic activity of B. cereus isolates and may indicate an higher diarrheic potential than anticipated.