Midelet-Bourdin Graziella, Leleu Guylaine, Malle Pierre
Agence Française de Sécurité Sanitaire des Aliments, Laboratoire d'Etudes et de Recherches sur les produits de la pêche, Boulogne sur Mer, France.
J Food Prot. 2007 Apr;70(4):891-900. doi: 10.4315/0362-028x-70.4.891.
Retail seafood products were analyzed on their use-by date using the international reference methods NF EN ISO 11290-1 and 11290-2 (collectively method R) or an in-house method (method B) for the isolation of Listeria monocytogenes. The sensitivity of the methods was about 78%. Method R detected more positive samples of smoked salmon and herb-flavored slices of smoked salmon than did method B, whereas the reverse was true for samples of carpaccio-like salmon, herb-flavored slices of raw salmon, and smoked trout. Most products produced a positive result after the first of two enrichments, and little difference was observed after changing the isolation medium (Listeria selective agar, L. monocytogenes blood agar, agar for Listeria according to Ottaviani and Agosti, Oxford agar, and Palcam agar). L. monocytogenes was isolated from 151 (27.8%) of the 543 samples, with concentrations mostly below 100 CFU/g. The pathogen prevalence and concentration in these seafood products varied greatly depending on the producer and the nature of the product. In certain cases, these differences could be explained by problems in cleaning and disinfection operations in the food-processing environment. The identities of L. monocytogenes isolates were confirmed by PCR, and isolates were characterized by random amplification of polymorphic DNA and pulsed-field gel electrophoresis (PFGE). PFGE patterns obtained with the enzymes Apal and AscI produced 26 different pulsotypes. In general, different pulsotypes were present in the different categories of seafood products and were not specific to one producer. The genetic diversity observed in the products was not related to the prevalence found at the manufacturing site. It is therefore important for producers to determine the source(s) of contamination of their product so the risks linked to the presence of L. monocytogenes can be reduced.
采用国际参考方法NF EN ISO 11290-1和11290-2（统称为方法R）或内部方法（方法B）对零售海鲜产品的保质期进行分析，以分离单核细胞增生李斯特菌。这些方法的灵敏度约为78%。与方法B相比，方法R检测出的烟熏三文鱼和香草味烟熏三文鱼片的阳性样本更多，而对于生牛肉片样三文鱼、香草味生三文鱼片和烟熏鳟鱼样本，情况则相反。大多数产品在两次富集的第一次后就产生了阳性结果，更换分离培养基（李斯特菌选择性琼脂、单核细胞增生李斯特菌血琼脂、奥塔维亚尼和阿戈斯蒂李斯特菌琼脂、牛津琼脂和Palcam琼脂）后观察到的差异很小。从543个样本中的151个（27.8%）分离出了单核细胞增生李斯特菌，其浓度大多低于100 CFU/g。这些海鲜产品中病原体的流行率和浓度因生产商和产品性质而异。在某些情况下，这些差异可以通过食品加工环境中清洁和消毒操作的问题来解释。通过PCR确认了单核细胞增生李斯特菌分离株的身份，并通过随机扩增多态性DNA和脉冲场凝胶电泳（PFGE）对分离株进行了特征分析。用Apal和AscI酶获得的PFGE图谱产生了26种不同的脉冲型。一般来说，不同的脉冲型存在于不同类别的海鲜产品中，并非特定于某一个生产商。产品中观察到的遗传多样性与生产现场发现的流行率无关。因此，生产商确定其产品的污染源很重要，这样可以降低与单核细胞增生李斯特菌存在相关的风险。
