An immunoassay for detection of heat-stable proteases from thermoduric psychrotrophic Bacillus spp. of dairy origin

A homogeneous preparation of a thermostable protease from Bacillus sp. B-17 was used to raise an antiserum in rabbits. IgG of this antiserum was used to study the antigenic relationship of proteases in cell-free extracts of 21 bacilli of milk origin. Based on immunological cross reactivity, the 21 bacilli were divided into 3 serological subgroups. To raise antibodies of broader specificity, protease from Bacillus sp. B-11 (group II) and B-3 (group III) were purified, mixed with purified B-17 protease, and an antiserum was raised against this mixture. IgG of this antiserum was purified (IgG anti-bacilli protease). A sandwich ELISA was standardized using IgG anti-bacilli protease as capture antibody. The assay could detect 1.2 ng ml(-1) of protease in milk or buffer, but the assay failed to detect 4 of 21 bacilli proteases. The results suggest that this assay is useful for the detection of proteases of Bacillus spp. in dairy industry.