Evaluation of a new culture medium for the enumeration and isolation of Streptococcus salivarius subsp. Thermophilus from cheese,Food Microbiology

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Evaluation of a new culture medium for the enumeration and isolation of Streptococcus salivarius subsp. Thermophilus from cheese
Food Microbiology ( IF 5.3 ) Pub Date : 2020-11-03 , DOI: 10.1016/j.fm.2020.103672
Noam Shani , Dino Isolini , Daniel Marzohl , Hélène Berthoud

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.

中文翻译：

评价一种新的培养基，用于唾液链球菌亚种的计数和分离。芝士嗜热菌

唾液链球菌亚种的计数和分离。奶酪中的嗜热菌具有挑战性，因为它可能具有相对较高的种类。

我们描述培养基SPY9.3用于唾液链球菌亚种的培养。奶酪中的嗜热菌。将培养基和相关的孵育条件（SPY）与其他两种方案M17和ST进行了比较：通过平行培养55株唾液链球菌亚种评估了敏感性。热，和通过选择性的从3原料乳干酪属于20个不同的非目标物种和亚种和（ii）分离的细菌菌株60（ⅰ）平行培养。SPY9.3和M17的菌落计数相似（均数差异为0.07 log（cfu / mL），p  > 0.001），ST显着高于M17和SPY9.3（均数差异为0.42和0.48 log（cfu / mL），分别，p <0.001）。SPY比ST和M17更特异，分别有20％，40％和50％的被调查非目标物种能够生长。唾液链球菌亚种 嗜热菌，肠球菌和金黄色葡萄球菌在所有3种方案中均无法区分。只有SPY避免了德氏乳杆菌亚种的生长。乳酸菌。最后，ST和SPY表现出较高的唾液链球菌亚种回收率。奶酪中的嗜热菌菌落高于M17（分别调整后的log（cfu / mL）为5.6、5.5和3.0），并且非特异性分离物的比例最低。