Differentiation between probiotic and wild-type Bacillus cereus isolates by antibiotic susceptibility test and Fourier transform infrared spectroscopy (FT-IR)

Animal feed often contains probiotic Bacillus strains used as feed additives. Spores of the non-pathogenic B. cereus var. toyoi (product name Toyocerin®) are used. Distinguishing between toxic wild-type Bacillus cereus strains and this probiotic strain is essential for evaluating the quality and risk of feed. Bacillus cereus CIP 5832 (product name Paciflor®) was used as probiotic strain until 2001. The properties of the two probiotic strains are quite similar.Differentiating between probiotic strains and wild-type B. cereus strains is not easy. ß-lactam antibiotics such as penicillin and cefamandole exhibit an inhibition zone in the agar diffusion test of probiotic B. cereus strains which are not seen for wild-type strains. Therefore, performing the agar diffusion test first may make sense before FT-IR testing.When randomly checking these strains by Fourier transform infrared spectroscopy (FT-IR), the probiotic B. cereus strains were separated from wild-type B. cereus/B. thuringiensis/B. mycoides/B. weihenstephanensis strains by means of hierarchical cluster analysis. The discriminatory information was contained in the spectral windows 3000–2800 cm− 1 (“fatty acid region”), 1200–900 cm− 1 (“carbohydrate region”) and 900–700 cm− 1 (“fingerprint region”). It is concluded that FT-IR spectroscopy can be used for the rapid quality control and risk analysis of animal feed containing probiotic B. cereus strains.