涂布平板计数法与MPN法定量检测禽肉和蛋中沙门菌的比较

Quantitative detection of Salmonella in poultry and shell eggs from retail market by PCA and MPN methods

为选择良好的禽肉和鸡蛋中沙门菌定量检测方法 ,通过染菌实验 ,分析比较了涂布平板计数法和MPN法 ,结果表明平板计数法优于MPN法。应用平板计数法检测了 16份鸡蛋和 2 6份禽肉试样。沙门菌检出限分别为 1CFU ml和 10 0CFU g。 16份蛋类试样中均未检出沙门菌。 2 6份鸡肉试样中 ,2 0份为沙门菌阳性 ,阳性率为 77%。其中 9份试样沙门菌数低于检出限 10 0CFU g ,其余试样菌数范围为 1 5× 10 2 ～ 2 5× 10 5CFU g。对 3份 - 2 0℃保存 5d的阳性禽肉试样应用MPN法进行了冷冻前后沙门菌含量的比较分析 ,储存后的菌数比冷冻前略有增加。实验结果表明 ,在食物试样中杂菌污染严重或沙门菌水平较低的情况下 ,平板法不能准确进行沙门菌计数 ,仍需进行MPN定量检测。

To develop a quantitative method for detecting Salmonella in poultry and shell eggs, comparison and analysis of the results of inoculation experiments were performed by using the plate count agar (PCA) method and the Most Probable Number (MPN) method. It indicated that PCA method was superior to MPN method. 16 shell egg samples and 26 raw chicken samples from a supermarket in Beijing were examined by using PCA method. The detection limits of Salmonella were 1 CFU/ml for eggs and 100 CFU/g for poultry. All the egg samples were Salmonella negative and 20 out of the 26 chicken samples were Salmonella positive. The contamination rate of chicken samples was 77%. The contamination level of 9 poultry samples was less than the detection limit 100 CFU/g. The contamination levels of other positive poultry samples were in the range of 1 5×10 2～2 5×10 5 CFU/g. Comparison and analysis of Salmonella amounts in the 3 positive poultry samples before and after freezing and kept at -20 ℃ for 5 d were performed by using MPN method. The Salmonella levels after freezing were a little higher than before. It proved that PCA method was not able to count Salmonella colonies accurately if the sample was heavily contaminated by other microorganisms. MPN method could be an alternative in this case.