Jang Mi Seon, Sahastrabuddhe Sushant, Yun Cheol-Heui, Han Seung Hyun, Yang Jae Seung
Clinical Immunology, Sciences Unit, International Vaccine Institute, Seoul, Republic of Korea; Department of Oral Microbiology and Immunology, DRI, and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul, Republic of Korea.
Program Management Unit, International Vaccine Institute, Seoul, Republic of Korea.
Microb Pathog. 2016 Aug;97:19-26. doi: 10.1016/j.micpath.2016.05.013. Epub 2016 May 20.
Typhoid fever, mainly caused by Salmonella enterica serovar Typhi (S. Typhi), is a life-threatening disease, mostly in developing countries. Enzyme-linked immunosorbent assay (ELISA) is widely used to quantify antibodies against S. Typhi in serum but does not provide information about functional antibody titers. Although the serum bactericidal assay (SBA) using an agar plate is often used to measure functional antibody titers against various bacterial pathogens in clinical specimens, it has rarely been used for typhoid vaccines because it is time-consuming and labor-intensive. In the present study, we established an improved SBA against S. Typhi using a semi-automated colony-counting system with a square agar plate harboring 24 samples. The semi-automated SBA efficiently measured bactericidal titers of sera from individuals immunized with S. Typhi Vi polysaccharide vaccines. The assay specifically responded to S. Typhi Ty2 but not to other irrelevant enteric bacteria including Vibrio cholerae and Shigella flexneri. Baby rabbit complement was more appropriate source for the SBA against S. Typhi than complements from adult rabbit, guinea pig, and human. We also examined the correlation between SBA and ELISA for measuring antibody responses against S. Typhi using pre- and post-vaccination sera from 18 human volunteers. The SBA titer showed a good correlation with anti-Vi IgG quantity in the serum as determined by Spearman correlation coefficient of 0.737 (P < 0.001). Taken together, the semi-automated SBA might be efficient, accurate, sensitive, and specific enough to measure functional antibody titers against S. Typhi in sera from human subjects immunized with typhoid vaccines.
伤寒热主要由伤寒沙门氏菌（S. Typhi）引起，是一种危及生命的疾病，在发展中国家最为常见。酶联免疫吸附测定（ELISA）被广泛用于定量血清中抗伤寒沙门氏菌的抗体，但无法提供功能性抗体滴度的信息。虽然使用琼脂平板的血清杀菌试验（SBA）常用于测量临床标本中针对各种细菌病原体的功能性抗体滴度，但由于其耗时且劳动强度大，很少用于伤寒疫苗的检测。在本研究中，我们使用带有24个样本的方形琼脂平板的半自动菌落计数系统建立了一种改进的针对伤寒沙门氏菌的SBA。半自动SBA有效地测量了用伤寒Vi多糖疫苗免疫的个体血清中的杀菌滴度。该试验对伤寒沙门氏菌Ty2有特异性反应，但对其他无关肠道细菌（包括霍乱弧菌和福氏志贺菌）无反应。与成年兔、豚鼠和人类的补体相比，幼兔补体是针对伤寒沙门氏菌的SBA更合适的补体来源。我们还使用18名人类志愿者接种疫苗前后的血清，检测了SBA和ELISA在测量针对伤寒沙门氏菌的抗体反应方面的相关性。SBA滴度与血清中抗Vi IgG量显示出良好的相关性，Spearman相关系数为0.737（P < 0.001）。综上所述，半自动SBA可能足够高效、准确、灵敏和特异，能够测量用伤寒疫苗免疫的人类受试者血清中针对伤寒沙门氏菌的功能性抗体滴度。
