乙型鏈球菌(Group B Streptococcus; GBS; 學名 Streptococcus agalactiae)是一種常見於人類胃腸道和泌尿生殖道菌相的細菌，對多數成年人來說是無害的，但卻被認為是新生兒感染及死亡的重要原因。根據研究指出大約有20%的婦女帶有GBS，而分娩正是新生兒感染的最大途徑，受GBS感染的新生兒往往會導致嚴重的併發症，如肺炎、腦膜炎及敗血症，即使感染後存活也會有嚴重的神經系統後遺症，因此及早檢測，適當投藥就可以有效降低新生兒感染的風險。根據美國疾病管制局(CDC)的規範，懷孕婦女需在35-37週時進行GBS感染的檢測，而傳統的細菌琣養檢測流程約需3-5天，相當耗時，在新發展的real-time PCR檢測法中為了得到足夠的核酸量也需要一天的細菌培養時間，對於面臨早產的婦女來說，皆無法提供即時的檢測。本實驗室發展已久的環狀指叉型電動力學晶片搭配影像分析技術能夠在低濃度的樣本中，藉由聚集細菌的顆粒來快速量化生菌數，來達成快速檢測的目的，唯其限制需在導電度低於30 μS/cm的環境下使用，因此本研究基於特異性辨識乙型鏈球菌之需求與傳統生產之去氧核酸適體以及抗體於在低導電度環境下會因缺少離子穩定結構，因而降低其效能，利用在低導電度環境中進行系統性配體演化指數擴增法(SELEX)來篩選選出可用於電動力學晶片之去氧核酸適體。本研究經由15輪的篩選後，並藉次世代定序(NGS)分析之結果挑選出現頻率最高之3條DNA序列作為核適體候選者。利用流式細胞儀進行初步功能性分析，結果顯示在核適體濃度1 mM下帶有螢光標定核適體的GBS仍小於5%，雖特異性表現良好，但仍需更多方法評估親和力。未來可對SELEX篩選流程進行修改，並加入於一般導電度下篩選之實驗成果來進行更深入的探討，以及評估於低導電度溶液中篩選核適體之可行性。

Group B streptococcus (GBS; scientific name Streptococcus agalactiae) is a commensal bacterium of human microbiota that is usually found in gastrointestinal and genitourinary tracts. GBS is usually asymptomatic for adults but is considered to be a necessary reason for newborn infection. According to a previous study, about 20% of women are colonized with GBS and it is the most route of GBS transmission for neonatal infection. Newborns infected with GBS often cause serious complications, such as pneumonia, meningitis, sepsis, and remain neurologic impairment after survival. Therefore, early detection and proper administration can effectively reduce the risk of neonatal infection. According to the Guidelines of the National Center for Disease Control and Prevention (CDC), the optimal timing for prenatal GBS screening is 35 to 37 weeks. The traditional culture testing process takes about 3 to 5 days, which is quite time-consuming. In the newly developed real-time PCR detection method, to obtain a sufficient amount of nucleic acid, it takes 18 to 24 h of bacterial culture time, which cannot provide immediate detection for women who face premature birth. The long-developed ring-shaped interdigital electrokinetic chip combined with image analysis technology in this laboratory can quickly quantify the number of bacteria in a low-concentration sample by collecting bacterial particles to achieve the purpose of rapid detection, but the limitation is that it can only be used in a low-conductivity sample (<30 μS/cm). This study is based on the need to specifically identify GBS and the traditional-produced DNA aptamers and antibodies will lack ions to stabilize its structure in the low conductivity environment, thereby reducing its effectiveness. Systematic ligand evolution index amplification (SELEX) was used in a low-conductivity environment to select DNA aptamers in this study. After 15 rounds of screening and using the next-generation sequencing (NGS) analysis, the three DNA sequences with the highest frequency were selected as aptamer candidates. Preliminary functional analysis using flow cytometry showed that the percentage of fluorescent GBS at aptamer concentration of 1 mM is still less than 5%. Although the specificity is good, more methods are still needed to verify the affinity. In the future, the SELEX process can be modified, and the further discussion could be done by comparing the results of screening GBS aptamer under general conductivity and evaluate the feasibility of screening aptamers in low conductivity solutions.

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