[Stability of MIC values from tetracyclines in different media (author's transl)]

The influence of nutrient-broth (NB), Mueller-Hinton-broth (MHB), isotonic-sensitive-broth (ISB) and tryptone-soya-broth (TSB) with respect to the determination of MIC values of three tetracyclines is shown. A difference of degradation of tetracycline derivates in the four media was found. The degradation in NB after 18 h was negligible, but in MHB after 18 h all the three tetracyclines were inactivated up to 42%. The MIC levels of staphylococcus aureus strains in NB were about twofold lower than those in MHB and TSB. The MIC levels in ISB were even three- to fourfold higher than in NB. From these results sensitivity testing of tetracycline derivates should be carried out with NB.