23-valent polysaccharide vaccine (PPSV23)-targeted serotype-specific identification of Streptococcus pneumoniae using the loop-mediated isothermal amplification (LAMP) method.

Jiwon Lee,Tomonori Hoshino,Chika Takano,Eun Jin Kim,Donghyun Lee,Mitsuko Seki,Paul E Kilgore,Takahiro Iijima,Satoshi Hayakawa,Yeongjun Baek,Bin Chang,Youngbae Yoon,Dong Wook Kim

doi:10.1371/journal.pone.0246699

Abstract

Reports of invasive disease due to Streptococcus pneumoniae have declined since the introduction of pneumococcal conjugate vaccines (PCV7 and PCV13). The incidence of invasive diseases due to S. pneumoniae that are not addressed by the vaccines, however, has increased in children and adults, creating a global public health problem. Previously, we established the loop-mediated isothermal amplification (LAMP) method for a PCV13 serotype-specific assay. In the current study, we developed a rapid, simple, and cost-effective assay to detect serotypes in the 23-valent pneumococcal polysaccharide vaccine (PPSV23) using the LAMP method. In this study, LAMP primer sets for serotypes 2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20, 22F, and 33F of S. pneumoniae were developed. The reactivity, specificity, and sensitivity of LAMP assays were determined and compared to those of conventional PCR. The feasibility of LAMP assays in clinical application in patients with invasive pneumococcal diseases was validated by defining the detection limit of the LAMP assay with bacterial genomic DNA-spiked blood specimens. The specificity of each LAMP assay was determined using 44 serotypes of pneumococcal strains. Their sensitivity was 100 copies per reaction versus 103 to 106 copies per reaction for PCR assays. Using DNA-spiked blood specimens, excluding the LAMP assay that targeted serotype 22F (103 copies per reaction), the limit of detection of the LAMP assay was similar to that with purified DNA as the template (102 copies per reaction), compared with 103 to >106 copies per reaction for PCR assays. In conclusion, a rapid and simple LAMP-based PPSV23-targeted serotype detection assay was developed for use in many countries. This study is the first report of a LAMP-based assay for identification of PPSV23 serotypes. Further evaluation of this assay is needed through surveillance and vaccine efficacy studies.

Highlights

Pneumonia is an important infectious disease with high morbidity and mortality [1, 2]
Fifty-five strains of S. pneumoniae, including serotypes that belong to PCV7, PCV13, and PPSV23 and non-vaccine serotypes, were analyzed in this study (Table 1)
We evaluated the analytical reactivity and specificity of LAMPbased pneumococcal serotyping using two non-pneumococcal species and 55 pneumococcal strains that belonged to 44 pneumococcal serotypes (Table 1)

Summary

Introduction

Pneumonia is an important infectious disease with high morbidity and mortality [1, 2]. A 23-valent polysaccharide vaccine (PPSV23) was introduced in the early 1980s, and pneumococcal conjugate vaccines (PCV7 or 13) have been available for children younger than 5 years since 2009; at least 10 other PCVs, containing 10–20 serotypes, are undergoing clinical trials [6]. PPSV23 contains 12 of the serotypes in PCV13 and an additional 11 serotypes (2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20, 22F, and 33F). PPSV23 is recommended for prevention of invasive pneumococcal diseases (IPDs) among all adults aged 65 years and in high-risk adults aged 19–64 years [5]. Administration of PCV to those older than 5 years may be useful in control of outbreaks in older children and adults [7]

Methods

Results

Conclusion