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目的研究大肠埃希菌在水中的存活时间及影响存活时间的因素。方法将大肠埃希菌加标于灭菌生理盐水和无菌自来水中制成模拟水样,分别在4℃和室温(25℃)下存放90 d,用Live/Dead荧光染色镜检法确定细菌总数和活菌总数,用胰大豆蛋白胨琼脂(TSA)和平板计数琼脂(PCA)确定细菌的可培养数。结果大肠埃希菌加标于水中,在90 d内细菌总数未发生较大变化;在生理盐水中,活菌总数未发生较大变化,4℃低温条件下可培养菌数逐渐下降为0,在25℃室温条件下可培养菌数下降3个数量级;在无菌自来水中,可培养菌数逐渐下降为0,4℃低温条件下活菌总数未发生较大变化,25℃室温条件下活菌总数逐渐下降为0。结论在4℃低温诱导下,大肠埃希菌在水中可进入活的非可培养状态;在室温下,大肠埃希菌在水中可保持较长时间的可培养性;富营养的TSA琼脂检测的菌落数多于寡营养的PCA琼脂;用平板涂布法检测水中的大肠埃希菌可能低估了肠道致病菌污染的风险。
Objective To study the survival time of Escherichia coli in water and the factors affecting survival time. Methods Escherichia coli was spiked in sterilized saline and sterile tap water to make simulated water samples. The samples were stored for 90 days at 4 ℃ and room temperature (25 ℃) respectively. The bacteria were identified by Live / Dead fluorescence microscopy Total number of viable cells, total number of viable cells, number of viable cells of the bacteria was determined using tryptic soy agar (TSA) and plate count agar (PCA). Results Escherichia coli spiked in water showed no significant change in the total number of bacteria within 90 days. In physiological saline, the total number of viable cells did not change significantly. The number of viable bacteria decreased to 0 at 4 ℃, The number of culturable bacteria decreased by 3 orders of magnitude at room temperature of 25 ° C. In sterile tap water, the number of culturable bacteria gradually decreased to 0,4 ° C. The total number of viable bacteria did not change significantly under the condition of low temperature. Under 25 ° C room temperature, The total number of bacteria decreased gradually to zero. Conclusions Escherichia coli can enter into live non-culturable state under the condition of low temperature of 4 ℃, Escherichia coli can maintain culturability in water for a long time under room temperature, and the eutrophication of TSA agar More colonies than oligotrophic PCA agar; detection of Escherichia coli in water by plate coating may underestimate the risk of intestinal pathogenic contamination.