Shani Noam, Isolini Dino, Marzohl Daniel, Berthoud Hélène
Agroscope, Competence Division Methods Development and Analytics, Research Group Fermenting Organisms, Schwarzenburgstrasse 161, 3003, Bern, Switzerland.
Agroscope, Competence Division Methods Development and Analytics, Research Group Fermenting Organisms, Schwarzenburgstrasse 161, 3003, Bern, Switzerland.
Food Microbiol. 2021 May;95:103672. doi: 10.1016/j.fm.2020.103672. Epub 2020 Nov 3.
Enumeration and isolation of Streptococcus salivarius subsp. thermophilus from cheese is challenging, due to the relatively high number of species it may host. We describe medium SPY9.3 for the cultivation of S. salivarius subsp. thermophilus from cheese. The medium and related incubation conditions (SPY) was compared with 2 other protocols, M17 and ST: sensitivity was assessed by parallel cultivation of 55 strains of S. salivarius subsp. thermophilus, and selectivity by (i) parallel cultivation of 60 strains belonging to 20 different non-target species and sub-species and (ii) isolating bacteria from 3 raw-milk cheeses. Colony counts were similar on SPY9.3 and M17 (mean difference 0.07 log(cfu/mL), p > 0.001) and significantly higher on ST than on M17 and SPY9.3 (mean differences 0.42 and 0.48 log(cfu/mL), respectively, p < 0.001). SPY was more specific than ST and M17, with respectively 20%, 40%, and 50% of the investigated non-target species able to grow. S. salivarius subsp. thermophilus, Enterococcus spp., and Staphylococcus aureus were indistinguishable using all 3 protocols. Only SPY avoided growth of Lactobacillus delbrueckii subsp. lactis. Finally, ST and SPY displayed higher recoveries of S. salivarius subsp. thermophilus colonies from cheese than M17 (5.6, 5.5, and 3.0 adjusted log(cfu/mL), respectively) and the lowest proportion of non-specific isolates. The protocol described here and based on SPY9.3 presents a promising alternative to existing protocols for the enumeration and isolation of S salivarius subsp. thermophilus from cheese or other complex fermented products.
从奶酪中分离和计数嗜热唾液链球菌亚种具有挑战性，因为奶酪中可能存在的菌种数量相对较多。我们描述了用于从奶酪中培养嗜热唾液链球菌亚种的SPY9.3培养基。将该培养基及相关培养条件（SPY）与其他两种方法M17和ST进行了比较：通过平行培养55株嗜热唾液链球菌亚种评估敏感性，通过（i）平行培养属于20个不同非目标菌种和亚种的60株菌株以及（ii）从3种生乳奶酪中分离细菌评估选择性。在SPY9.3和M17上的菌落计数相似（平均差异0.07 log（cfu/mL），p>0.001），且在ST上显著高于M17和SPY9.3（平均差异分别为0.42和0.48 log（cfu/mL），p<0.001）。SPY比ST和M17更具特异性，分别有20%、40%和50%的被研究非目标菌种能够生长。使用所有三种方法均无法区分嗜热唾液链球菌亚种、肠球菌属和金黄色葡萄球菌。只有SPY能抑制德氏乳杆菌乳酸亚种的生长。最后，与M17相比，ST和SPY从奶酪中回收嗜热唾液链球菌亚种菌落的效率更高（分别为5.6、5.5和3.0调整对数（cfu/mL）），且非特异性分离株的比例最低。本文基于SPY9.3描述的方法为从奶酪或其他复杂发酵产品中分离和计数嗜热唾液链球菌亚种提供了一种有前景的替代现有方法的方案。
