影响检测生活饮用水中菌落总数的相关因素探讨

Discussion on related factors affecting detection of total bacterial count in drinking water

参考GB 4789.2—2016对GB/T 5750.12—2006生活饮用水中菌落总数的检测方法加以改进,比较了培养基种类、培养温度、实验操作方法等对计数数据的影响。结果发现,使用平板计数琼脂经30℃培养7 d后菌落总数的计数,比营养琼脂相同条件下的计数提高了1倍以上;涂布平板法比倒平板法更易计数;营养修复不能缩短检测时间,反而使水中菌落数出现减少或增殖现象。采用改进后方法,即平板计数琼脂培养基、涂布平板、30℃培养7 d,对62个水样进行了检测。统计分析后发现水样中菌落可分为两大类,一类特点是菌落易生长且单一,当培养3 d与2 d计数比值<2时,培养3 d就接近生长最高峰,培养7 d时检测结果Y=-0.387+1.155X(R=0.989,X为3 d计数);另一类特点是菌落生长缓慢且有多种色素菌,当培养3 d与2 d计数比值≥2时,需培养7 d才到最高峰值,培养7 d时检测结果Y=27.455+2.525X(R=0.928,X为3 d计数数据)。新方法只需培养3 d,根据培养3 d与2 d计数的比值及相应的回归方程,即可预测培养7 d时的计数结果。但新方法的计数普遍增大,故建议对GB/T 5750.12—2006方法和现有生活饮用水的菌落总数判定限值进行合理的修订。

Referring to GB 4789.2-2016,the detection method of total bacterial count in drinking water(GB/T 5750.12-2006)was improved by comparing the effects of culture medium type,culture temperature and experimental operation method on the count data.The results showed that the total bacterial count data of plate counting agar after culturing at 30℃for 7 days was more than doubled higher than that of nutrient agar under the same conditions;coating plate method was easier to count than inverted plate method;nutritional repair could not shorten the detection time,but reduced or proliferated the number of bacteria in water.The improved method,plate counting agar culture medium at 30℃for 7 days,was used to detect 62 water samples.After statistical analysis,it was found that the colonies in water samples could be divided into two categories.The characteristics of one type were easy to grow and single colony.When the ratio of counting results of 3 d to 2 d was less than 2,the counting of 3 d was close to the peak of growth,and the detection result of 7 d culture was Y=-0.387+1.155X(R=0.989,X was 3 d counting data).Another type was characterized by slow colony growth and a variety of pigmented bacteria.When the ratio of counting results of 3 d to 2 d was≥2,it took 7 days of culture to reach the peak and the detection result Y=27.455+2.525X(R=0.928,X was 3 d counting data).According to the ratio of counting data at 3 d to 2 d and the corresponding regression formula,the counting results at 7 days could be predicted.It was suggested that the GB/T 5750.12-2006 method and the determination limit of total bacterial count in drinking water should be revised reasonably.