Phytomedicine Programme, Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa.
Planta Med. 2021 Aug;87(10-11):836-840. doi: 10.1055/a-1482-1410. Epub 2021 May 6.
Many scientists investigate the potential of finding new antibiotics from plants, leading to more than a thousand publications per year. Many different minimum inhibitory concentrations of extracts have been proposed to decide if an extract has interesting activity that could lead to the discovery of a new antibiotic. To date, no rational explanation has been given for the selection criteria different authors have used. The cumulative percentage of plant extracts with different activities from a large experiment determining the activity of 714 acetone tree leaf extracts of 537 different South African tree species against 4 nosocomial pathogenic bacteria and 2 yeasts was calculated using a widely accepted serial dilution microplate method with -iodonitrotetrazolium violet as indicator of growth. All the extracts were active at a concentration of 2.5 mg/mL. The formula, % of active extracts = 439 × minimum inhibitory concentration in mg/mL, describes the results for minimum inhibitory concentrations below 0.16 mg/mL, with a correlation coefficient of 0.9998. A rational approach could be to determine the minimum inhibitory concentrations of the most active 1, 3, 9, 25, 50, and > 50% of a large number of plant extracts investigated against these six important microbial pathogens. Starting with an extract concentration of 10 mg/mL, I propose the following classification based on minimum inhibitory concentrations: OUTSTANDING ACTIVITY: < 0.02 mg/mL, EXCELLENT ACTIVITY: 0.021 - 0.04 mg/mL, VERY GOOD ACTIVITY: 041 - 0.08 mg/mL, GOOD ACTIVITY: 0.081 - 0.16 mg/mL, AVERAGE ACTIVITY: 0.161 - 0.32 mg/mL, and WEAK ACTIVITY: > 0.32 mg/mL. Higher minimum inhibitory concentrations may still be effective in ethnopharmacological studies.
许多科学家研究从植物中寻找新抗生素的潜力，导致每年有超过一千篇相关文献发表。为了判断提取物是否具有可能导致发现新抗生素的有趣活性，已经提出了许多不同的最小抑菌浓度提取物。迄今为止，对于不同作者使用的选择标准，尚未给出合理的解释。
使用广泛接受的连续稀释微孔板法，以碘硝基四唑紫为生长指示剂，对 714 种丙酮树叶片提取物（来自 537 种不同南非树种）对 4 种医院内致病性细菌和 2 种酵母的活性进行了大型实验，计算了不同活性的植物提取物的累积百分比。所有提取物在 2.5 mg/mL 的浓度下均具有活性。公式为 %活性提取物 = 439×mg/mL 最小抑菌浓度，用于描述 0.16 mg/mL 以下的最小抑菌浓度结果，相关系数为 0.9998。
一种合理的方法可以是确定对这六种重要微生物病原体具有最高活性的 1%、3%、9%、25%、50%和>50%的大量植物提取物的最小抑菌浓度。从 10 mg/mL 的提取物浓度开始，我基于最小抑菌浓度提出了以下分类：
<0.02 mg/mL，优秀活性：0.021-0.04 mg/mL，非常好活性：0.041-0.08 mg/mL，良好活性：0.081-0.16 mg/mL，中等活性：0.161-0.32 mg/mL，和微弱活性：>0.32 mg/mL。较高的最小抑菌浓度在民族药理学研究中仍可能有效。
