Detection of penicillin G in milk using a conductimetric method.

A highly sensitive method was developed that used conductance measurement for the detection of penicillin G in milk. The method is based on the inhibition by the antibiotic on the growth of Bacillus stearothermophilus ATCC 10149. The conductance change in PM indicator agar containing the bacterial spores was continuously monitored at 55 degrees C by a microbiological analyzer, and the detection time was delayed when penicillin G was present in the samples. The detection limit of the method for penicillin G was .00016 IU/ml with a detection time of about 3.4 h, but only a narrow range (.00016 to .00062 IU/ml) of the antibiotic could be quantitatively analyzed. The conductimetric method is about 30 times more sensitive than several methods currently used. In addition, the conductance measurement is fully automatic, and multiple samples, 120 or 240, can be analyzed simultaneously.