Genotypic Distribution of Alpha-Like Proteins in Group B Streptococcus Strains Isolated in Korea: Implications for Vaccine Coverage

Abstract

Background: Group B Streptococcus (GBS) is a major cause of invasive bacterial diseases, including sepsis, meningitis, and pneumonia, particularly in newborns and infants. Pregnant adults, those with pre-existing conditions, and older adults are particularly susceptible. Ongoing research is focused on developing various vaccines utilizing different antigens, including capsular polysaccharides and alpha-like proteins (Alps). Epidemiological data on these antigens in GBS is essential for predicting the effectiveness of these vaccines. However, no epidemiological studies on Alps genotype have been conducted in Korea. This study aimed to fill this gap by investigating the distribution and characteristics of the alp genotype in domestic clinical strains.

Materials and methods: We analyzed 386 GBS strains isolated from various clinical specimens between April 2000 and November 2018. The serotype of each strain was initially verified using a slide latex agglutination reaction, then confirmed by polymerase chain reaction to determine the presence of the genes bca, rib, alp1, alp2, alp3, and alp4 associated with Alps. Strains were then classified as invasive or non-invasive based on the type of clinical specimen. The distribution of serotypes and alp genotype was analyzed across these classifications.

Results: We analyzed 386 bacterial strains to assess their clinical characteristics, serotypes, and alp genotype distributions. Of these strains, 47.1% (182 strains) were invasive primarily isolated from blood samples (43.3%, 167 strains), whereas non-invasive strains were more frequently isolated from sites such as the vagina and urethra. Serotype III was the most prevalent across both invasive and non-invasive strains, comprising 28.2% (109 strains) of all isolates. Notably, 79.5% (307 strains) of all isolates were encompassed by the hexavalent vaccine (serotype Ia, Ib, II, III, and V) formulations. Furthermore, the rib genotype was the most common, detected in 39.4% (152 strains) of all isolates, with a higher prevalence in non-invasive samples (44.1%, 90 strains).

Conclusion: Although the distribution of alp genotypes differed between invasive and non-invasive strains, the proportion of bca and rib was substantial. Therefore, Alp protein vaccine containing Rib and Cα antigens is expected to provide protection against prevalent GBS strains in Korea. Additional epidemiological studies on GBS vaginal colonization in pregnant women and invasive neonatal strains are needed to support early neonatal sepsis prevention in these high-risk groups.

Keywords: Genotype; Infant; Serogroup; Streptococcus agalactiae; Vaccine.

Figure 1. Serotypes distribution of group B Streptococcus isolated in invasive and non-invasive strains (A). Serotype coverage comparison of trivalent (blue dashed line) and hexavalent vaccines (red dashed line) (B).

Figure 2. alp genotype distribution of group B Streptococcus isolated in invasive and non-invasive strains (A). The bca and rib genotypes, which have been extensively studied in the context of vaccines and are clinically significant, appear to constitute 72.3% of the samples (red dashed line) (B).

Figure 3. Serotypes and alp genotypes distribution of group B Streptococcus isolated in invasive strains. The serotype coverage of the trivalent vaccine (solid blue line) is 64.8%, while the serotype coverage of the hexavalent vaccine (dashed red line) is 86.26%. The bca and rib genotypes were identified in 67.6% of invasive strains.