MC与M17琼脂在嗜热链球菌计数中的比对研究

Comparative study of MC and M17 agar in enumeration of Streptococcus thermophilus

目的评价国标中使用的MC琼脂与ISO标准中使用的M17琼脂在嗜热链球菌计数中的优劣。方法按照GB 4789.35-2016,使用MC琼脂与M17琼脂对2种以嗜热链球菌为主要成分的菌粉,以及含有嗜热链球菌的发酵乳,进行了计数比对。结果使用M17琼脂对菌粉和发酵乳中嗜热链球菌计数,其计数值均高于采用MC琼脂的计数值,对于2种菌粉样品和发酵乳样品, M17琼脂计数值较MC琼脂分别高出116%、89%和30%;对配对计数结果进行了t检验分析,差异具有极显著性(P<0.01)。且分组数据的方差分析表明,与MC琼脂计数结果相比, M17琼脂计数结果的方差更小,精密度更高。结论对于嗜热链球菌的计数, M17琼脂在回收率、精密度和实用性方面显著优于MC琼脂。

Objective To evaluate the pros and cons of MC agar used in GB method and M17 agar used in ISO method for Streptococcus thermophilus counting.Methods According to GB 4789.35-2016,2 starter cultures of Streptococcus thermophilus were enumerated and compared by using MC and M17 agar,as well as fermented milk containing Streptococcus thermophilus.Results For the 2 starter cultures and fermented milk samples,the enumeration of M17 agar for Streptococcus thermophilus was 116%,89%and 30%higher than that of MC agar;the paired count results were analyzed by t-test,and the difference was extremely significant(P<0.01).And the ANOVA of the grouped data showed that the enumeration of M17 agar had smaller variance and higher precision,compared with MC agar.Conclusion For enumeration of Streptococcus thermophilus,M17 agar is significantly better than MC agar in terms of recovery,precision and practicability.