Development and application of a centrifugation-plating method to study the biodiversity of Bacillus species in rice products

A centrifugation-plating method was developed, using amylase and Tween 80 pre-treatment, for detection and enumeration of Bacillus spp. in rice products. The high sensitivity of this method improved detection of a variety of Bacillus species in rice products compared to the spread-plate method. Bacillus spp. were detected in 33 out of 35 raw rice samples with the centrifugation-plating method, but only 13 samples using the spread-plating method, even though 1 mL of a 10−1 sample dilution was used, to increase sensitivity of the method. Known toxigenic or potentially toxigenic species (Bacillus cereus/Bacillus thuringiensis, Bacillus subtilis, Bacillus licheniformis, and Bacillus pumilus) were those most frequently found in both raw and cooked rice.