ISO 16649-3:2015规定了一种检测和计数β-葡萄糖醛酸酶阳性大肠杆菌的水平方法，方法是通过液体培养基培养技术和计算在（37±1）°C和（44±1）°C下培养后的最大可能数（MPN）。ISO 16649的这一部分适用于以下情况: -供人类食用和动物饲养的产品； -食品生产和食品处理领域的环境样本。 该方法适用于大肠杆菌细胞的计数，这些细胞可能因脱水、冷冻、暴露于盐水（如海洋）环境或氯等消毒剂的损害而承受压力- 包含产品。 ISO 16649本部分的适用性受到该方法对很大程度可变性的敏感性的限制。该方法旨在根据第11条给出的信息应用和解释结果。 尚未对所有基质（如牛奶和奶制品）对该方法进行全面评估。ISO 7251旨在用于牛奶和奶制品。

ISO 16649-3:2015 specifies a horizontal method for the detection and enumeration of β-glucuronidase positive Escherichia coli, by means of the liquid-medium culture technique and calculation of the most probable number (MPN) after incubation at (37 ± 1) °C, then at (44 ± 1) °C. This part of ISO 16649 is applicable to the following: - products intended for human consumption and the feeding of animals; - environmental samples in the area of food production and food handling. The method is suitable for the enumeration of cells of E. coli that might have been subjected to stress arising from dehydration, freezing, and exposure to a saline (such as marine) environment or damage by disinfectants such as chlorine-containing products. A limitation of the applicability of this part of ISO 16649 is imposed by the susceptibility of the method to a large degree of variability. The method is intended to be applied and the results interpreted in the light of the information given in Clause 11. This method has not been fully evaluated for all matrices (e.g. for milk and milk products). ISO 7251 is intended to be used for milk and milk products.