Identification of isolates
One hundred and sixty-nine colonies with the typical morphology of B. cereus on MYP medium were isolated. They were all Gram-positive and catalase-positive, and they produced endospores and grew under anaerobic condition. Spore position was central or subterminal and did not swell the sporangium. Among these isolates, 96 and 98% were confirmed as B. cereus by ISO 7932 and NF V 08–058 procedures, respectively; 83 isolates confirmed as B. cereus by both procedures were selected to represent each kind of product and storage condition, and were characterized by API-50CHB and API-20E strips ( Table 2). Most strains belonged to the API-profile B. cereus 1 and to the profile intermediate between B. cereus and B. mycoides. These latter strains formed a homogenous group which all had similar API-profiles. These two profiles were found among strains isolated from purées stored at both 10 °C and room temperature ( Table 2). Strains with the profile B. cereus 2 were unable to use starch and were isolated only from cooked vegetables. Strains with the API profile B. cereus 1 were isolated from both vegetable purées and cooked vegetables, whereas strains with a profile intermediate between B. cereus and B. mycoides were isolated mostly from vegetable purées.
Growth temperature
None of the isolates of B. cereus were able to grow at 2 °C; 10% grew at 5 °C and 63% at 10 °C. All the strains with the API profile B. cereus 2 were unable to grow at 10 °C or below ( Table 3). All strains grew at 37 °C and 81% at 42 °C ( Table 3). This latter group was mostly strains unable to grow at 5 °C, or to grow rapidly at 10 °C (i.e., giving a turbid culture within 3 or 7 days).
Table 3. Numbers of Bacillus cereus strains * which grew at temperatures ranging from 5 to 42 °C