Ferron P, Michard J
Laboratoire Interrégional de la Direction Générale de la Concurrence, de la Consommation et de la Répression des Fraudes, Rennes, France.
Int J Food Microbiol. 1993 Jun 1;18(4):289-303. doi: 10.1016/0168-1605(93)90152-7.
Three hundred samples of pastry from 100 different suppliers in western France, including butter-cream, whipped dairy cream and custard filled cakes from each supplier, were collected and tested for the occurrence of Listeria spp. in 25 g samples. Listeria spp. were detected in 21.7% of he samples: Listeria monocytogenes in 13.7%, Listeria innocua in 10% and Listeria seeligeri in 2.3%. Thirteen samples were contaminated with two species simultaneously. The frequency of contaminated samples was not related to the composition of the pastry filling used, but it seemed to increase with the number of aerobic contaminant microorganisms in the dairy cream-based samples. The contamination rate was dependent on the place of manufacture. The numbers of Listeria spp. and Listeria monocytogenes were estimated on positive samples at the 25 g level as follows: < 0.3/g, Listeria spp. in 47 samples, L monocytogenes in 27; 0.3-30/g, Listeria spp. in 13, L. monocytogenes in nine; 30-300/g, L. monocytogenes in one; 300-3000/g; L. monocytogenes in three; 700,000/g, L. monocytogenes in one. Various detection methods were tested, including two enrichments broths tested in parallel: a modified LEB broth using 10 mg/l acriflavine-HCl and the UVM 1 broth, with incubation at 30 degrees C and streaking onto PALCAM agar. The enrichment procedures were: (a) primary enrichment of 25 g sample and plating after 48 h and 7 days; (b) secondary enrichment by subculturing the primary enrichment broths incubated for 24 h and 6 days, into fresh enrichment broth, then plating after 24 h incubation; (c) pre-enrichment of 25 g sample for 24 h in the basal enrichment broths without inhibitors, followed by subculturing in complete broths which were plated after 24 h and 6 days incubation. In all cases, UVM performed better than the LEB broth. It was unnecessary to extend the primary enrichment period beyond 48 h. Secondary enrichments inoculated from 24-h incubated primary enrichments gave a slightly better isolation rate than primary enrichments. Secondary enrichments made from 6-day incubated primary enrichments gave no additional advantage. The pre-enrichment procedure had an efficiency higher than that obtained by primary enrichment.
收集了法国西部100家不同供应商的300份糕点样本，每个供应商的样本包括奶油夹心、鲜奶油和蛋奶馅蛋糕，对25克样本中的李斯特菌属进行检测。21.7%的样本检测出李斯特菌属：其中13.7%为单核细胞增生李斯特菌，10%为无害李斯特菌，2.3%为斯氏李斯特菌。13个样本同时被两种菌污染。受污染样本的频率与所用糕点馅料的成分无关，但似乎随着基于乳制品奶油的样本中需氧污染物微生物数量的增加而增加。污染率取决于生产地点。在25克水平的阳性样本上估计的李斯特菌属和单核细胞增生李斯特菌数量如下：<0.3/g，李斯特菌属47个样本，单核细胞增生李斯特菌27个；0.3 - 30/g，李斯特菌属13个，单核细胞增生李斯特菌9个；30 - 300/g，单核细胞增生李斯特菌1个；300 - 3000/g，单核细胞增生李斯特菌3个；700,000/g，单核细胞增生李斯特菌1个。测试了多种检测方法，包括两种平行测试的增菌肉汤：一种使用10毫克/升盐酸吖啶黄的改良LEB肉汤和UVM 1肉汤，在30℃下培养并划线接种到PALCAM琼脂上。增菌程序如下：(a)对25克样本进行初次增菌，48小时和7天后进行平板接种；(b)通过将培养24小时和6天的初次增菌肉汤转接至新鲜增菌肉汤进行二次增菌，然后在培养24小时后进行平板接种；(c)将25克样本在无抑制剂的基础增菌肉汤中预增菌24小时，然后转接至完全肉汤中，在培养24小时和6天后进行平板接种。在所有情况下，UVM的效果均优于LEB肉汤。没有必要将初次增菌时间延长至48小时以上。从培养24小时的初次增菌物转接的二次增菌物的分离率略高于初次增菌物。从培养6天的初次增菌物进行的二次增菌没有额外优势。预增菌程序的效率高于初次增菌。
