Microcalorimetric investigation of the toxic action of berberine on Tetrahymena thermophila BF5

Tetrahymena thermophila (T. thermophila) BF₅ produces heat through growth and metabolism. By microcalorimetry, the power‐time curves of the metabolism of T. thermophila BF₅ at 28 °C were measured and some quantitative parameters were obtained from these curves. Then the action of berberine on this microbe was investigated. Furthermore, the minimum inhibitory concentration (MIC) of berberine against T. thermophila BF₅ growth was obtained by tube dilution method. Berberine of different concentrations had various actions on T. thermophila BF₅ growth: a low concentration (25 μg/ml) of berberine began to inhibit the growth of T. thermophila BF₅ and a high concentration (450 μg/ml) of berberine completely inhibited T. thermophila BF₅ growth. The toxic action of berberine could also be expressed as half‐inhibitory concentration IC₅₀, i.e., 50% effective in this inhibition. The value of IC₅₀ was 175.60 μg/ml, while the MIC of this compound against T. thermophila BF₅ was 20.76 mg/ml. Berberine has strong toxic action on T. thermophila BF₅ growth. The microcalorimetric method for the assay of toxic action is quantitative, inexpensive and versatile. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)