Oravcová K, Trncíková T, Kuchta T, Kaclíková E
Department of Microbiology and Molecular Biology, Food Research Institute, Bratislava, Slovakia.
J Appl Microbiol. 2008 Feb;104(2):429-37. doi: 10.1111/j.1365-2672.2007.03554.x. Epub 2007 Sep 21.
Detectability of Listeria monocytogenes at 10(0) CFU per food sample in the presence of Listeria innocua using standard microbiological detection was evaluated and compared with the real-time PCR-based method.
Enrichment in half-Fraser broth followed by subculture in Fraser broth according to EN ISO 11290-1 was used. False-negative detection of 10(0) CFU L. monocytogenes was obtained in the presence of 10(1) CFU L. innocua per sample using the standard detection method in contrast to more than 10(5) CFU L. innocua per sample using real-time PCR. Identification of L. monocytogenes on the chromogenic medium by the standard procedure was impossible if L. innocua was able to overgrow L. monocytogenes by more than three orders of magnitude after the enrichment in model samples. These results were confirmed using naturally contaminated food samples.
Standard microbiological method was insufficient for the reliable detection of 10(0) CFU L. monocytogenes in the presence of more than 10(0) CFU of L. innocua per sample. On the other hand, if the growth of L. monocytogenes was sufficient to reach the concentration equal to the detection limit of PCR, the amount of the other microflora present in the food sample including L. innocua was not relevant for success of the PCR detection of L. monocytogenes.
After the enrichment, the PCR detection is more convenient than the standard one as PCR detection is not compromised by other present microflora.
评估在无害李斯特菌存在的情况下，使用标准微生物检测方法检测每份食品样品中10⁰CFU的单核细胞增生李斯特菌的可检测性，并与基于实时PCR的方法进行比较。
采用根据EN ISO 11290-1在半弗雷泽肉汤中富集，然后在弗雷泽肉汤中传代培养的方法。使用标准检测方法时，在每份样品存在10¹CFU无害李斯特菌的情况下，对10⁰CFU单核细胞增生李斯特菌的检测出现假阴性，而使用实时PCR时，每份样品存在超过10⁵CFU无害李斯特菌时也能检测到。如果无害李斯特菌在模型样品富集后能够比单核细胞增生李斯特菌生长超过三个数量级，通过标准程序在显色培养基上鉴定单核细胞增生李斯特菌是不可能的。使用天然污染的食品样品证实了这些结果。
标准微生物方法不足以在每份样品存在超过10⁰CFU无害李斯特菌的情况下可靠地检测10⁰CFU单核细胞增生李斯特菌。另一方面，如果单核细胞增生李斯特菌的生长足以达到等于PCR检测限的浓度，食品样品中存在的包括无害李斯特菌在内的其他微生物数量与单核细胞增生李斯特菌的PCR检测成功与否无关。
富集后，PCR检测比标准检测更方便，因为PCR检测不受其他现存微生物的影响。
