Food Sciences Department, Faculty of Veterinary Medicine, University of Liège, Sart Tilman, B43b Liege, B-4000 Belgium.
BMC Microbiol. 2011 Aug 4;11:178. doi: 10.1186/1471-2180-11-178.
The contamination of raw milk cheeses (St-Marcellin and Brie) from two plants in France was studied at several steps of production (raw milk, after addition of rennet - St-Marcellin - or after second maturation - Brie -, after removal from the mold and during ripening) using bifidobacteria as indicators of fecal contamination.
Bifidobacterium semi-quantitative counts were compared using PCR-RFLP and real-time PCR. B. pseudolongum were detected in 77% (PCR-RFLP; 1.75 to 2.29 log cfu ml(-1)) and 68% (real-time PCR; 2.19 to 2.73 log cfu ml(-1)) of St-Marcellin samples and in 87% (PCR-RFLP; 1.17 to 2.40 log cfu ml(-1)) of Brie cheeses samples. Mean counts of B. pseudolongum remained stable along both processes. Two other populations of bifidobacteria were detected during the ripening stage of St-Marcellin, respectively in 61% and 18% of the samples (PCR-RFLP). The presence of these populations explains the increase in total bifidobacteria observed during ripening. Further characterization of these populations is currently under process. Forty-eight percents (St-Marcellin) and 70% (Brie) of the samples were B. pseudolongum positive/E. coli negative while only 10% (St-Marcellin) and 3% (Brie) were B. pseudolongum negative/E. coli positive.
The increase of total bifidobacteria during ripening in Marcellin's process does not allow their use as fecal indicator. The presence of B. pseudolongum along the processes defined a contamination from animal origin since this species is predominant in cow dung and has never been isolated in human feces. B. pseudolongum was more sensitive as an indicator than E. coli along the two different cheese processes. B. pseudolongum should be used as fecal indicator rather than E. coli to assess the quality of raw milk and raw milk cheeses.
对法国两家工厂生产的生奶奶酪（圣马塞林奶酪和布里奶酪）进行了研究，在生产的多个步骤（生奶、添加凝乳酶后-圣马塞林奶酪-或二次成熟后-布里奶酪-、从模具中取出后和成熟过程中）使用双歧杆菌作为粪便污染的指示物。
使用 PCR-RFLP 和实时 PCR 比较双歧杆菌半定量计数。在 77%（PCR-RFLP；1.75 至 2.29 log cfu ml(-1)) 和 68%（实时 PCR；2.19 至 2.73 log cfu ml(-1))的圣马塞林奶酪样品中检测到短双歧杆菌，在 87%（PCR-RFLP；1.17 至 2.40 log cfu ml(-1))的布里奶酪样品中检测到。短双歧杆菌的平均计数在两个过程中保持稳定。在圣马塞林奶酪的成熟阶段还检测到另外两个双歧杆菌种群，分别在 61%和 18%的样品中（PCR-RFLP）。这些种群的存在解释了成熟过程中总双歧杆菌的增加。目前正在对这些种群进行进一步的特征描述。48%（圣马塞林）和 70%（布里）的样品为短双歧杆菌阳性/大肠埃希氏菌阴性，而只有 10%（圣马塞林）和 3%（布里）的样品为短双歧杆菌阴性/大肠埃希氏菌阳性。
在马塞林工艺的成熟过程中总双歧杆菌的增加不允许将其用作粪便指示物。在生产过程中存在双歧杆菌，表明其来自动物来源的污染，因为该物种在牛粪中占优势，从未在人类粪便中分离出来。在两种不同的奶酪生产过程中，短双歧杆菌比大肠埃希氏菌作为指示物更为敏感。应该使用短双歧杆菌而不是大肠埃希氏菌作为粪便指示物来评估生奶和生奶奶酪的质量。
