乳酸菌除了存在於人體內的正常菌叢中外，在今日人類的生活中也幾乎成了不可或缺的角色，具有改善乳糖不耐症、增強免疫力、營養補給等益處。然而，最常被應用做發酵食品的Streptococcus屬之乳酸菌為S. thermophilus，此菌被研究得也最多，本研究的目的在探討Streptococcus屬的另一種產乳酸菌：S. lactis的生理特性。
本實驗的目的是從市面販售，用以家庭自製優格常用之乾燥菌粉－－「纖綠菌寶寶」中分離出格蘭氏陽性的成串球菌後，以生化檢驗法加以鑑定種類，並對其生理特性加以探討。探討的生理特性主要為S. lactis在一般之Yeast Glucose Lemco broth中、改變培養液之滲透壓後，在37℃下的生長情形；另外針對該菌的耐酸、耐膽鹽及對抗生素之敏感特性作試驗，並定量其產生的維生素B12及維生素B6。
在一般之Yeast Glucose Lemco broth中，自培養後4小時起，生長速度增快，12小時之後，就達到靜止期（stationary phase），故可在12~14小時之內就培養足夠的菌數。而改變NaCl濃度後，在濃度低於7.5%的培養液中都可生長，但在8.5%以上的濃度時就無法存活。
S. lactis對pH 3.0的酸性環境有耐受性，約可存活2-3小時；但對膽鹽則完全無耐受性。S. lactis對抗生素中的Penicillin G、Gentamicin、Erythromycin及Streptomycin具有抗藥性，而對Ampicillin和Chloramphenicol則無。
至於產生維生素的情形，以微生物檢驗法定量的結果：每mL的S. lactis 菌液可產生 0.1994 ng 的維生素B12，亦可產生 3.8374 ng 的維生素B6。

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