利用嗜熱菌Bacillus stearothermophillus var. cali dolactis對青黴素與鏈黴素之感受性差異很大的特性，在鏈黴素之存在下，可以不受干擾地直接以此菌為實驗菌種，而測定出青黴素之力價。依據報告，0.004μ/ml之青黴素即對B. stearot hermophillus var. calidolact is有抑制作用，而鏈黴素則需至5-8 γ/ml的濃度才對之有抑制能力。利用此一特性，可期在鏈黴素一青黴素之複合劑中，不經預先破壞鏈黴素或分離二成份之前處理之情況下，能直接以圓筒平碟法定量其中青黴素之力價。 With the characteristic high sensitivity to penicillin (about 0.004 u/ml) and rather low sensitivity to streptomycin (about 5-8 γ/ml) , the thermophilic bacillus stearothermophillus var. calidolactis is used as the test organism in the microbiological assay (by agar diffusion method) to determine the potency of penicillin in the mixture of streptomycin/penicillin(500mg/400,000 u) without any pretreatment and give a satisfactory results.
