微生物平板计数方法的标准化与量化差异分析

Standardization and quantitative difference analysis of microbial plate counting methods

摘要:

背景 药品、食品和化妆品的微生物污染控制是保障质量安全的核心，而平板计数法是目前微生物限度检查中应用最广泛的方法。然而，国内外相关计数标准之间仍存在一定差异。目的 明确国内外药品、食品、化妆品领域微生物平板计数相关标准在计数规则、误差评估、修约与报告要求上的差异及其对检测结果的影响，为《中国药典》2025年版微生物计数规则的标准化落地实施、国内各实验室检测数据的一致性与结果可比性提升提供科学依据。方法 梳理国内外标准的技术要求，以金黄色葡萄球菌(Staphylococcus aureus)为测试菌株构建多稀释系列平行平板计数模型，通过对数似然比统计量、平板间误差率、相对标准偏差等指标评估不同标准的误差控制效果，比较“四舍五入”与“只进不舍”修约规则的离散度差异，并验证不同报告规则对计数结果的影响幅度。结果 不同标准的计数误差判定限值差异显著，导致相同平板数据在部分标准下判定为合格、部分标准下判定为不合格。“四舍五入”修约规则的标准差(0.34)略低于“只进不舍” (0.41)，数据离散度更优。多稀释度计数场景中不同报告规则导致结果偏差最高可达9.6%。结论 国内外微生物计数标准的规则差异会导致计数结果出现显著偏差，影响检测结果的准确性与跨标准可比性。基于实验数据，建议我国药品微生物计数规则在误差判定中引入统计学验证方法、统一修约规则为“四舍五入”、优化报告规则的加权计算逻辑，以实现与国际主流标准的科学对接，提升我国相关产品的质量监管一致性与国际贸易互认水平。

Abstract:

Background Microbial contamination control of drugs, foods, and cosmetics is central to ensuring quality and safety, while the plate count method is currently the most widely used approach for microbial limit testing. However, certain differences still exist between domestic and international standards for plate counting.Objective To clarify the differences in counting rules, error evaluation, rounding and reporting requirements among domestic and international standards for microbial plate counting in the fields of pharmaceuticals, food, and cosmetics, as well as their impacts on test results, so as to furnish scientific, evidence for the standardized implementation of microbial counting rules of the Chinese Pharmacopoeia (2025 Edition) and the improvement of the consistency and comparability of detection data across domestic laboratories.Methods Technical requirements of domestic and international standards were systematically sorted out. A multi-dilution series parallel plate counting model was established with Staphylococcus aureus as the test strain. The error control effects of different standards were evaluated based on indicators including the log-likelihood ratio statistic, inter-plate error rate, and relative standard deviation. The data dispersion performance was compared between the “rounding off” and “rounding up” rules, and the impact ranges of different reporting rules on counting results were verified.Results Significant differences were observed in the limit values for counting error judgment among different standards, resulting in the same plate data being judged as qualified under some standards and unqualified under others. The “rounding off” rule had slightly lower standard deviation (SD=0.34) than the “rounding up” rule (SD=0.41), demonstrating better data dispersion performance. In the scenario of multi-dilution counting, the maximum deviation caused by different reporting rules could reach 9.6%.Conclusion The differences in rules among domestic and international standards for microbial counting can lead to significant deviations in counting results, affecting the accuracy of test results and cross-standard comparability. On the basis of experimental data, it is recommended that statistical verification methods be introduced into the error judgment of microbial counting rules in Chinese pharmaceutical standards, “rounding off” be adopted as the rounding rule, and the weighted calculation logic of reporting rules be optimized. These measures are expected to achieve scientific alignment with international mainstream standards and enhance the consistency of quality supervision and the level of mutual recognition in international trade for related products in China.