Simplified identification of aerobic spore-formers in the investigation of foods

Bacillus spp. are among the main spoilage organisms in food due to their versatile metabolism and heat-resistant spores. Except for B. cereus, no specific identification method is available, although information about Bacillus spp. would be useful in monitoring good manufacturing practice. A simplified identification scheme for aerobic spore-formers for routine laboratory use was elaborated by reducing the number of tests to be performed; 20 Bacillus spp. common in foods were considered. Besides cell morphology six biochemical characters were selected that proved most efficient in identification. In addition, methods were developed and modified to determine these characters by only 3 tests. By applying the simplified identification scheme, 766 strains of bacilli isolated from various foods were tested and species identity of 714 strains (93%) could be determined. Most aerobic spore-formers from foods were B. subtilis, B. pumilus and B. licheniformis. The spectrum of mesophilic bacilli isolated from natural sources was broad and comprised some 20 different species. Only one-third of the thermophilic isolates proved to be identical with, or similar to, B. stearothermophilus, while the rest were identified as five other species. The simplified method merits main application in ecological studies of foods.