奶和奶制品.微生物实验室内质量控制.第2部分:平行板和后续稀释步骤的菌落计数可靠性测定

[中文适用范围]： ISO 14461 的这一部分 | IDF 169 描述了使用菌落计数方法评估微生物计数结果的常规程序，随后进行 10 倍稀释步骤，并在每个稀释步骤中使用一个板或两个平行板。 每个进行菌落计数的实验室都会定期应用此常规程序。 它提供了平行板和后续稀释步骤结果之间差异的可接受性标准，如下所示。 a) 将平行板获得的结果（菌落计数）与给定菌落计数的表格限值进行比较。 如果超过这些限制，则可能表明执行并行测定时存在技术问题。 b) 将两个连续 10 倍稀释步骤的两个平行板的结果（菌落计数总和）与给定菌落计数总和的表格限值进行比较。 如果超过这些限制，则可能表明执行稀释时存在技术问题。 c) 如果超出上述限值的情况多于预期，则表明测试程序缺乏可靠性。 注：第 7 章给出并解释了表 1 和表 2 中数值的计算公式。 [外文原描述]： ISO 14461-2|IDF 169-2:2005 describes a routine procedure for the evaluation of results of the enumeration of microorganisms using colony-count methods with subsequent 10-fold dilution steps and one plate or two parallel plates within each dilution step. This routine procedure is applied regularly in each laboratory performing colony counts. It provides criteria for the acceptability of differences between the results from parallel plates and subsequent dilution steps, as follows. The results (colony counts) obtained from parallel plates are compared with tabulated limits for given colony counts. If these limits are exceeded, a technical problem when performing the parallel determinations may be indicated. The results (sums of colony counts) of two parallel plates of two subsequent 10-fold dilution steps are compared with tabulated limits for given sums of colony counts. If these limits are exceeded, a technical problem when performing the dilutions may be indicated. If the limits mentioned above are exceeded in more cases than expected, this indicates that the test procedure lacks reliability.