Serotype Distribution, Virulence, and Antibiotic Resistance Genomic Characterization of Group B Streptococcus — China, 1998–2024

Xiaodong Ren; Xiao Liu; Yanqing Che; Luyao Yang; Yixin Mao; Mengjie Li; Zhiwen Sun; Xuemei Bai; He Gao; Yimin Wang; Duochun Wang

doi:10.46234/ccdcw2025.069

Article Navigation > China CDC Weekly > 2025, 7(13): 413-421

Vital Surveillances: Serotype Distribution, Virulence, and Antibiotic Resistance Genomic Characterization of Group B Streptococcus — China, 1998–2024

Xiaodong Ren^1,2,&;
Xiao Liu^2,&;
Yanqing Che^1,2;
Luyao Yang^1,2;
Yixin Mao^2,3;
Mengjie Li^1,2;
Zhiwen Sun²;
Xuemei Bai²;
He Gao²;
Yimin Wang^1, ,;
Duochun Wang^2, ,

View author affiliations

Abstract
Introduction
Streptococcus agalactiae, or group B Streptococcus (GBS), can cause severe infections in humans, yet comprehensive genomic characterization from China remains limited. This study presents an extensive genomic analysis of GBS isolates collected in China from 1998 to 2024.
Methods
GBS genomes were obtained from public databases and through de novo sequencing. Serotype confirmation was conducted via pan-genomic analysis, phylogenetic relationships were established using maximum-likelihood methodology, and virulence and antibiotic resistance genes were identified through the Virulence Factor Database and Comprehensive Antibiotic Resistance Database. Statistical analyses were performed using SPSS 26.0, primarily employing Fisher’s exact tests.
Results
Analysis of 747 GBS genomes revealed eight serotypes (Ia, Ib, II, III, IV, V, VI, VII) and nontypeable strains. Serotypes III, Ib, Ia, V, and II constituted 96.65% of all isolates. GBS prevalence remained low from 1998–2011 but increased substantially after 2012. Geographic distribution demonstrated significant regional heterogeneity. Phylogenetic analysis categorized the 747 genomes into five distinct lineages, with lineage 5 being predominant. Six virulence factor categories encompassing 56 virulence-associated genes were identified, with 33 genes present in nearly all genomes. Twenty-seven antibiotic resistance genes spanning nine drug classes were detected, particularly those conferring resistance to peptides and macrolide antibiotics, indicating widespread antimicrobial resistance mechanisms in GBS.
Conclusions
GBS infections in China exhibit serotype distributions similar to global patterns but with notable regional variations. This comprehensive genomic characterization provides critical insights for developing targeted prevention strategies and treatment approaches for GBS infections in China.
Conflict of interest: No conflicts of interest.
Funding: Supported by the National Science and Technology Infrastructure of China (NPRC-32) and the construction of protein fingerprints of rare pathogens (KFYJ-2022-039)

Author Affiliations

1.
School of Public Health, Lanzhou University, Lanzhou City, Gansu Province, China
2.
National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China
3.
National Key Laboratory of Intelligent Tracking and Forecasting for Infectious Diseases, China CDC Key Laboratory of Environment and Population Health, National Institute of Environmental Health, Chinese Center for Disease Control and Prevention, Beijing, China
^& Joint first authors.

Corresponding authors: Yimin Wang, wangyimin@lzu.edu.cn; Duochun Wang, wangduochun@icdc.cn
Online Date: March 28 2025
Issue Date: March 28 2025
doi: 10.46234/ccdcw2025.069

References

[1]	Lancefield RC. A serological differentiation of human and other groups of hemolytic streptococci. J Exp Med 1933;57(4):571 − 95. https://doi.org/10.1084/jem.57.4.571.
[2]	Say L, Chou D, Gemmill A, Tunçalp Ö, Moller AB, Daniels J, et al. Global causes of maternal death: a WHO systematic analysis. Lancet Glob Health 2014;2(6):e323 − 33. https://doi.org/10.1016/s2214-109x(14)70227-x.
[3]	Lawn JE, Bianchi-Jassir F, Russell NJ, Kohli-Lynch M, Tann CJ, Hall J, et al. Group B streptococcal disease worldwide for pregnant women, stillbirths, and children: why, what, and how to undertake estimates? Clin Infect Dis 2017;65(suppl_2):S89-99. http://dx.doi.org/10.1093/cid/cix653.
[4]	Russell NJ, Seale AC, O’Driscoll M, O’Sullivan C, Bianchi-Jassir F, Gonzalez-Guarin J, et al. Maternal colonization with group b Streptococcus and serotype distribution worldwide: systematic review and meta-analyses. Clin Infect Dis 2017;65(suppl_2):S100 − 11. https://doi.org/10.1093/cid/cix658.
[5]	Madrid L, Seale AC, Kohli-Lynch M, Edmond KM, Lawn JE, Heath PT, et al. Infant group b streptococcal disease incidence and serotypes worldwide: systematic review and meta-analyses. Clin Infect Dis 2017;65(suppl_2):S160 − 172. https://doi.org/10.1093/cid/cix656.
[6]	Wang J, Zhang Y, Lin M, Bao JF, Wang GY, Dong RR, et al. Maternal colonization with group B Streptococcus and antibiotic resistance in China: systematic review and meta-analyses. Ann Clin Microbiol Antimicrob 2023;22(1):5. https://doi.org/10.1186/s12941-023-00553-7.
[7]	Francois Watkins LK, McGee L, Schrag SJ, Beall B, Jain JH, Pondo T, et al. Epidemiology of invasive group b streptococcal infections among nonpregnant adults in the united states, 2008-2016. JAMA Intern Med 2019;179(4):479 − 88. https://doi.org/10.1001/jamainternmed.2018.7269.
[8]	Lopes E, Fernandes T, Machado MP, Carriço JA, Melo-Cristino J, Ramirez M, et al. Increasing macrolide resistance among Streptococcus agalactiae causing invasive disease in non-pregnant adults was driven by a single capsular-transformed lineage, Portugal, 2009 to 2015. Euro Surveill 2018;23(21):1700473. https://doi.org/10.2807/1560-7917.Es.2018.23.21.1700473.
[9]	Cox LM, Yamanishi S, Sohn J, Alekseyenko AV, Leung JM, Cho I, et al. Altering the intestinal microbiota during a critical developmental window has lasting metabolic consequences. Cell 2014;158(4):705 − 21. https://doi.org/10.1016/j.cell.2014.05.052.
[10]	Slotved HC, Kong FR, Lambertsen L, Sauer S, Gilbert GL. Serotype IX, a proposed new Streptococcus agalactiae serotype. J Clin Microbiol 2007;45(9):2929 − 36. https://doi.org/10.1128/jcm.00117-07.
[11]	Li XO, Gao W, Jia ZL, Yao KH, Yang JY, Tong JJ, et al. Characterization of group b streptococcus recovered from pregnant women and newborns attending in a hospital in Beijing, China. Infect Drug Resist 2023;16:2549 − 59. https://doi.org/10.2147/idr.S395942.
[12]	Lee CC, Hsu JF, Prasad Janapatla R, Chen CL, Zhou YL, Lien R, et al. Clinical and microbiological characteristics of group b Streptococcus from pregnant women and diseased infants in intrapartum antibiotic prophylaxis era in Taiwan. Sci Rep 2019;9(1):13525. https://doi.org/10.1038/s41598-019-49977-2.
[13]	Sheppard AE, Vaughan A, Jones N, Turner P, Turner C, Efstratiou A, et al. Capsular typing method for Streptococcus agalactiae using whole-genome sequence data. J Clin Microbiol 2016;54(5):1388 − 90. https://doi.org/10.1128/jcm.03142-15.
[14]	Kapatai G, Patel D, Efstratiou A, Chalker VJ. Comparison of molecular serotyping approaches of Streptococcus agalactiae from genomic sequences. BMC Genomics 2017;18(1):429. https://doi.org/10.1186/s12864-017-3820-5.
[15]	Schubert A, Zakikhany K, Schreiner M, Frank R, Spellerberg B, Eikmanns BJ, et al. A fibrinogen receptor from group B Streptococcus interacts with fibrinogen by repetitive units with novel ligand binding sites. Mol Microbiol 2002;46(2):557 − 69. https://doi.org/10.1046/j.1365-2958.2002.03177.x.
[16]	Gutekunst H, Eikmanns BJ, Reinscheid DJ. The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells. Infect Immun 2004;72(6):3495 − 504. https://doi.org/10.1128/iai.72.6.3495-3504.2004.
[17]	Morello E, Mallet A, Konto-Ghiorghi Y, Chaze T, Mistou MY, Oliva G, et al. Evidence for the sialylation of PilA, the PI-2a pilus-associated adhesin of Streptococcus agalactiae strain NEM316. PLoS One 2015;10(9):e0138103. https://doi.org/10.1371/journal.pone.0138103.
[18]	Papasergi S, Brega S, Mistou MY, Firon A, Oxaran V, Dover R, et al. The GBS PI-2a pilus is required for virulence in mice neonates. PLoS One 2011;6(4):e18747. https://doi.org/10.1371/journal.pone.0018747.
[19]	Rosini R, Rinaudo CD, Soriani M, Lauer P, Mora M, Maione D, et al. Identification of novel genomic islands coding for antigenic pilus-like structures in Streptococcus agalactiae. Mol Microbiol 2006;61(1):126 − 41. https://doi.org/10.1111/j.1365-2958.2006.05225.x.
[20]	Mudzana R, Mavenyengwa RT, Gudza-Mugabe M. Analysis of virulence factors and antibiotic resistance genes in group B streptococcus from clinical samples. BMC Infect Dis 2021;21(1):125. https://doi.org/10.1186/s12879-021-05820-6.
[21]	Liu YX, Liu JH. Group B streptococcus: virulence factors and pathogenic mechanism. Microorganisms 2022;10(12):2483. https://doi.org/10.3390/microorganisms10122483.
[22]	Vornhagen J, Quach P, Boldenow E, Merillat S, Whidbey C, Ngo LY, et al. Bacterial hyaluronidase promotes ascending GBS infection and preterm birth. mBio 2016;7(3):e00781 − 16. https://doi.org/10.1128/mBio.00781-16.
[23]	Vornhagen J, Adams Waldorf KM, Rajagopal L. Perinatal Group B streptococcal infections: virulence factors, immunity, and prevention strategies. Trends Microbiol 2017;25(11):919 − 31. https://doi.org/10.1016/j.tim.2017.05.013.
[24]	Wu BQ, Su JZ, Li L, Wu WY, Wu JS, Lu YM, et al. Phenotypic and genetic differences among group B Streptococcus recovered from neonates and pregnant women in Shenzhen, China: 8-year study. BMC Microbiol 2019;19(1):185. https://doi.org/10.1186/s12866-019-1551-2.
[25]	Jerlström PG, Talay SR, Valentin-Weigand P, Timmis KN, Chhatwal GS. Identification of an immunoglobulin A binding motif located in the beta-antigen of the c protein complex of group B streptococci. Infect Immun 1996;64(7):2787 − 93. https://doi.org/10.1128/iai.64.7.2787-2793.1996.
[26]	Ernst CM, Staubitz P, Mishra NN, Yang SJ, Hornig G, Kalbacher H, et al. The bacterial defensin resistance protein MprF consists of separable domains for lipid lysinylation and antimicrobial peptide repulsion. PLoS Pathog 2009;5(11):e1000660. https://doi.org/10.1371/journal.ppat.1000660.
[27]	Caliot E, Firon A, Solgadi A, Trieu-Cuot P, Dramsi S. Lipid lysination by MprF contributes to hemolytic pigment retention in group B Streptococcus. Res Microbiol 2024;175(8):104231. https://doi.org/10.1016/j.resmic.2024.104231.
[28]	Sharkey LKR, Edwards TA, O’Neill AJ. ABC-F proteins mediate antibiotic resistance through ribosomal protection. mBio 2016;7(2):e01975. https://doi.org/10.1128/mBio.01975-15.
[29]	Dinos GP. The macrolide antibiotic renaissance. Br J Pharmacol 2017;174(18):2967 − 83. https://doi.org/10.1111/bph.13936.
[30]	Li PY, Wei Y, Li GQ, Cheng H, Xu ZC, Yu ZJ, et al. Comparison of antimicrobial efficacy of eravacycline and tigecycline against clinical isolates of Streptococcus agalactiae in China: in vitro activity, heteroresistance, and cross-resistance. Microb Pathog 2020;149:104502. https://doi.org/10.1016/j.micpath.2020.104502.
[31]	Hayes K, O’Halloran F, Cotter L. A review of antibiotic resistance in Group B Streptococcus: the story so far. Crit Rev Microbiol 2020;46(3):253 − 69. https://doi.org/10.1080/1040841x.2020.1758626.

FIGURE 1. Spatio-temporal distribution of GBS in China. (A) Temporal distribution of GBS in China; (B) Temporal distribution of GBS in China, percentage stacked bar chart.

Abbreviation: GBS=group B Streptococcus.

Download: Full-Size Img PowerPoint

FIGURE 2. Phylogenomic tree and distribution of virulence- and ARGs-associated genes across 747 Streptococcus agalactiae genomes. (A) Phylogenomic tree of 747 GBS genomes constructed using maximum likelihood method based on core gene sequences; (B) Distribution of virulence-associated genes across 747 GBS genomes; (C) Distribution of antibiotic resistance genes across 747 GBS genomes.

Note: Genes with comparable functions or those belonging to the same functional class have been integrated in the visualization.

Abbreviation: GBS=group B Streptococcus.

Download: Full-Size Img PowerPoint

TABLE 1. Serotype and isolation source distribution of GBS strains in China.

Serotype	Isolation source							Total (%)
Serotype	Blood	Genital secretion	Vaginal and rectal	Urine	Sputum	Others	Unknow	Total (%)
III	59	8	20	8	4	34	190	323 (43.24)
Ib	9	34	6	6	7	13	102	177 (23.69)
Ia	11	4	2	2	6	28	67	120 (16.06)
V	3	15	2	5	3	12	41	81 (10.84)
II	2	1	0	2	1	3	12	21 (2.81)
VI	1	1	1	1	0	1	11	16 (2.14)
IV	0	0	0	1	0	2	1	4 (0.54)
VII	0	0	0	0	0	0	1	1 (0.13)
NT	0	0	0	0	0	1	3	4 (0.54)
Total	85	63	31	25	21	94	428	747 (100)
Note: Columns 1 to 5 under isolation source represent the primary sample types, all of which were collected from humans. Others: Include cervical samples, milk, skin, fish farm, bovine sources, and additional specimen types. Abbreviation: GBS=group B Streptococcus.

Download: CSV

TABLE 2. Serotype and spatial distribution of GBS strains in China.

Region	Serotype*											Total
Region	Ⅰa	Ⅰb	Ⅱ	Ⅲ	Ⅳ	Ⅴ	Ⅵ	Ⅶ	Ⅷ	Ⅸ	NT	Total
Taiwan, China	51	22	8	155	0	16	11	1	0	0	0	264
Shandong	7	67	2	34	1	25	2	0	0	0	1	139
Henan	4	34	1	8	0	15	1	0	0	0	0	63
Hong Kong SAR	19	1	0	38	0	2	1	0	0	0	2	63
Shanghai	5	20	2	13	0	5	0	0	0	0	0	45
Beijing	2	7	0	6	0	1	0	0	0	0	0	16
Anhui	0	3	3	2	3	3	0	0	0	0	1	15
Guangdong	3	1	0	2	0	0	0	0	0	0	0	6
Jiangsu	1	1	1	0	0	1	1	0	0	0	0	5
Zhejiang	0	0	0	2	0	1	0	0	0	0	0	3
Guangxi	1	0	0	0	0	0	0	0	0	0	0	1
Hainan	1	0	0	0	0	0	0	0	0	0	0	1
Ningxia	1	0	0	0	0	0	0	0	0	0	0	1
Sichuan	0	0	0	1	0	0	0	0	0	0	0	1
Not collected	25	21	5	61	0	12	0	0	0	0	0	124
Total	120	177	22	322	4	81	16	1	0	0	4	747
Abbreviation: GBS=group B Streptococcus; Hong Kong SAR=Hong Kong Special Administrative Region. * P<0.001.

Download: CSV

TABLE 3. The classification of virulence-related factors of Streptococcus agalactiae.

VF category	Virulence genes	Virulence factor	Functions
Adherence	tufA, groEL, fbp54, pavA, lmb, scpA/scpB, srtC-1/srtB, srtC3, srtC4, pilC, pilA, GBS_RS03585, srtC2, GBS_RS03565, GBS_RS03570, srtC1, pilB, fbsB, fbsA	EF-Tu, GroEL, FBPs, PavA, Lmb, C5a peptidase, PI-2a, PI-1, FbsB, FbsA, RlrA islet	Adherence and colonization; promotes fibronectin-mediated collagen recruitment, adhesion and invasion; dissemination; impairs recruitment to sites of infection; biofilm formation; protein binding, recognizing the extracellular matrix; manipulates the host inflammatory response
Exoenzyme	hylB	Hyaluronidase	Dissemination, penetration
Exotoxin	acpC, cylD, cylB, cylF, cylI, cylJ, cylA, cylK, cylZ, cylG, cfa/cfb, cylE, cylX	Beta-haemolysin/cytolysin, CAMP factor	Forms pores in cell membrane; pro-inflammatory effects: induces apoptosis, promotes cellular invasion, and triggers iNOS and cytokine release
Immune modulation	hasC, GBS_RS06540, GBS_RS06555, neuA, neuC, wbtL, GBS_RS06585, GBS_RS06595, GBS_RS06600, GBS_RS06605, GBS_RS06610, neuB, cps4B, GBS_RS06580, GBS_RS06590, GBS_RS06570, GBS_RS06560, GBS_RS06565, GBS_RS06575, cba	Hyaluronic acid capsule, Capsule, LPS, Beta-C protein	Prevents phagocytosis; discourages C3b binding; binds to CD44, preventing the activation of the alternative complement pathway; inhibits complement-mediated opsonophagocytosis; LPS, resistant to complement deposition, masks cell wall-associated complement, preventing opsonophagocytosis
Nutritional/Metabolic factor	psaA	PsaA	Transport of Mn²+ and Zn²+ into bacterial cytoplasm, mutants impacts colonization and increase susceptibility to oxidative damage
Stress survival	clpP, bsh	ClpP, BSH	Serine protease involved in proteolysis and resisting the acute toxicity of bile and bile salts
Abbreviation: GBS=group B Streptococcus.

Download: CSV

Citation:

通讯作者: 陈斌, bchen63@163.com

1.
沈阳化工大学材料科学与工程学院沈阳 110142

Turn off MathJax

Article Contents

Get Citation

PDF

Article Metrics

Article views(309) PDF downloads(8) Cited by()

Introduction

Streptococcus agalactiae, or group B Streptococcus (GBS), can cause severe infections in humans, yet comprehensive genomic characterization from China remains limited. This study presents an extensive genomic analysis of GBS isolates collected in China from 1998 to 2024.

Methods

GBS genomes were obtained from public databases and through de novo sequencing. Serotype confirmation was conducted via pan-genomic analysis, phylogenetic relationships were established using maximum-likelihood methodology, and virulence and antibiotic resistance genes were identified through the Virulence Factor Database and Comprehensive Antibiotic Resistance Database. Statistical analyses were performed using SPSS 26.0, primarily employing Fisher’s exact tests.

Results

Analysis of 747 GBS genomes revealed eight serotypes (Ia, Ib, II, III, IV, V, VI, VII) and nontypeable strains. Serotypes III, Ib, Ia, V, and II constituted 96.65% of all isolates. GBS prevalence remained low from 1998–2011 but increased substantially after 2012. Geographic distribution demonstrated significant regional heterogeneity. Phylogenetic analysis categorized the 747 genomes into five distinct lineages, with lineage 5 being predominant. Six virulence factor categories encompassing 56 virulence-associated genes were identified, with 33 genes present in nearly all genomes. Twenty-seven antibiotic resistance genes spanning nine drug classes were detected, particularly those conferring resistance to peptides and macrolide antibiotics, indicating widespread antimicrobial resistance mechanisms in GBS.

Conclusions

GBS infections in China exhibit serotype distributions similar to global patterns but with notable regional variations. This comprehensive genomic characterization provides critical insights for developing targeted prevention strategies and treatment approaches for GBS infections in China.

HTML

Streptococcus agalactiae, classified as a group B streptococcus (GBS) (1), can exist as a commensal organism in the human gastrointestinal and genitourinary tracts while also causing severe infections in immunocompromised individuals and the elderly. In pregnant women, GBS infection is associated with maternal disease (2) and can cause early-onset or late-onset sepsis in newborns and hypoxic-ischemic encephalopathy in infants (3). The global prevalence of maternal GBS colonization is estimated at 18%, with significant regional variations. The pooled incidence of invasive GBS disease in infants is 0.49 per 1,000 live births, highest in Africa (1.12) and lowest in Asia (0.30) (4–5). In China, the maternal colonization rate is 8.1%, lower than the global average (6). GBS also represents a growing threat to immunocompromised individuals and the elderly (7).

Intrapartum antibiotic prophylaxis (IAP) effectively prevents GBS infections, but overuse of antibiotics contributes to increasing antibiotic resistance in GBS (8). Additionally, antibiotic exposure in newborns can have detrimental health effects (9). These concerns highlight the need for alternative treatment approaches, such as GBS vaccines. Capsular polysaccharides (CPs) are key virulence factors in GBS, with 10 recognized serotypes (Ia, Ib, II-IX) based on their immunological reactivity (10). Understanding the distribution of these serotypes is essential for the development of effective CPS-based vaccines (4). Currently, no vaccine is available for GBS infection. Clarifying GBS serotype distribution remains critical for developing effective prevention and treatment strategies, but studies in China are limited in scope and geographic coverage (6,11–12).

This study provides an extensive genomic characterization of GBS strains collected in China, aiming to investigate serotype and genotype distribution, genetic evolution, and the presence of virulence and antibiotic resistance genes. By elucidating the molecular and genomic epidemiological patterns of GBS in China, this research establishes a foundation for developing effective prevention and treatment strategies.

METHODS

Bacterial Strains, Whole-Genome Data Collection, and Sequencing

A total of 747 Streptococcus agalactiae genomes were analyzed in this study, comprising 721 publicly available genomes retrieved from the National Center for Biotechnology Information (NCBI) database (https://www.ncbi.nlm.nih.gov/datasets/genome/) as of April 2024, supplemented with 26 newly sequenced clinical isolates. The clinical strains were sequenced using the Illumina HiSeq 2000 platform (Novogene Technology Co., Ltd., Beijing, China), and genome annotation was performed using Prokka [version 1.13.3; Winnipeg Institute for Bacterial Genomics (PHAC), Winnipeg, Canada]. The basic information of all strains is provided in Supplementary Table S1.

Identification of Serotype, Virulence, and Antibiotic Resistance-Associated Genes

Serotype determination was conducted through CPs sequence analysis using pan-genomic comparison, with a threshold of ≥95% sequence identity required for serotype confirmation (13–14). Phylogenetic analyses were performed based on core single nucleotide polymorphisms (SNPs) using IQ-TREE (version 2.3.4; Computational Evolution Lab, Ho Chi Minh City, Vietnam). Virulence and antibiotic resistance genes were identified from Prokka-generated *.gff files using Roary (version 2.3.12; University of Exeter, Exeter, UK). Virulence genes were identified through BLASTp alignment against the Virulence Factors of Pathogenic Bacteria (VFDB, https://www.mgc.ac.cn/VFs/) database, applying stringent criteria (≥60% identity, ≥70% coverage, E-value ≤1×10^-5). Antibiotic resistance genes were identified using the Resistance Gene Identifier (RGI) [version 6.0.2; Comprehensive Antibiotic Resistance Database (McMaster University), Hamilton, Canada] against the Comprehensive Antibiotic Resistance Database (CARD, https://card.mcmaster.ca/home), with thresholds of ≥80% for both identity and coverage.

Statistical Analysis and Data Availability

Statistical analyses were conducted using SPSS (version 26.0; IBM Corp., Armonk, NY). Categorical variables were assessed using Fisher’s exact test, with statistical significance defined as P<0.01. This test was specifically employed to evaluate differences in serotype distribution of GBS across various geographical regions of China. The genome sequences of the 26 newly sequenced clinical GBS strains have been deposited in GenBank under BioProject ID PRJNA1128393.

DISCUSSION

Among the 747 GBS strains collected in China from 1998 to 2024, we identified eight serotypes and one non-typeable serotype, with serotypes III, Ib, Ia, V, and II constituting 96.65% of all isolates. This distribution closely aligns with both global (98%) and previously reported Chinese (95.9%) distributions (4,6). Notably, the prevalence of serotype III (43.24%) in our study exceeds the global average (25%) but approximates the previously reported Chinese average (46.4%), reflecting significant regional heterogeneity within China (4,6). These findings suggest that while the overall GBS serotype distribution in China mirrors global trends, substantial intra-national variations exist. Geographic distribution analysis revealed marked regional differences, with Beijing Municipality demonstrating a high proportion of serotype III (38.3%), while Taiwan, China reported higher prevalence of serotype VI (11–12). These observations underscore the pronounced geographical variations in GBS serotype distribution across China, emphasizing the necessity for region-specific surveillance studies. Temporal trend analysis indicates an increase in GBS cases, likely attributable to enhanced clinical awareness and advances in sequencing technologies, although the recent decline in case numbers may reflect the impact of coronavirus disease 2019 (COVID-19) pandemic disruptions or delays in sequencing data submission. Serotype III has maintained predominance throughout the study period, while serotype Ib has shown a notable increase in recent years, highlighting the critical importance of comprehensive serotype distribution data for targeted vaccine development strategies.

We identified six categories of virulence genes through VFDB analysis, comprising a total of 56 genes. The adhesion protein FbsA facilitates GBS binding to fibrinogen, thereby protecting the pathogen from phagocytosis (15), while fbsB enhances GBS invasion into host cells and promotes vaginal colonization (16). Several genes (SrtC1, SrtC2, GBS_RS03565, GBS_RS03570, and GBS_RS03585) are associated with the pili type PI-1 structure. The PI-2a pilus comprises three subunit proteins (PilA, PilB, PilC), whose assembly requires sortases SrtC3 and SrtC4, collectively facilitating GBS invasion and colonization (17-18). While pili structures represent potential vaccine targets, strains lacking pili islands must be considered in vaccine development strategies (19). The gene encoding hyaluronidase (hylB) demonstrated a carriage rate of 85.68%, comparable to the 97.8% reported in Zimbabwean isolates (20). This enzyme enables GBS to breach the placental barrier, ascend from the vagina, and infect the fetus (21), while its absence significantly reduces GBS’s capacity to invade fetal tissue and induce preterm delivery (22).

Exotoxin genes from the cyl gene family, cfa, and cfbs, together with the CAMP factor, are associated with β-hemolysis in GBS, causing tissue damage through lysis of human cells (21). The hemolytic properties of GBS play a crucial role in its pathogenesis and immune evasion mechanisms (23). The universal presence of cytochrome-encoding genes across all GBS strains suggests that targeting cytochrome functionality could represent a promising preventive strategy. Immunomodulatory genes, particularly those related to CPs, are critical virulence determinants, with CP-based vaccines currently under development. Our genomic analysis identified several virulence genes associated with CPs, with GBS_RS06560, GBS_RS06565, GBS_RS06570, and GBS_RS06575 being notably underrepresented in serotypes Ib, II, V, and VI. Comparative analysis of capsular polysaccharide composition between these and other strains may elucidate the functional impact of these genes on the capsular structure. CPs enhance GBS virulence by facilitating immune evasion, inhibiting opsonophagocytosis, and promoting biofilm formation (24). The cba gene, predominantly found in serotypes Ia and Ib, may confer protection against opsonophagocytosis (25). While the virulence genes identified in this study provide valuable insights into GBS pathogenicity in China, they represent only a partial characterization, necessitating additional strain data and experimental validation for comprehensive assessment.

Antimicrobial resistance genes conferring resistance to clindamycin, erythromycin, and tetracycline were prevalent among the analyzed strains, with Saga_mprF specifically associated with daptomycin resistance (26–27). The mreA gene and members of the erm gene family were widely distributed, contributing to macrolide-lincosamide-streptogramin B resistance, particularly against clindamycin and erythromycin (28–29). Among 278 strains lacking erm genes, 16 harbored both lsaE and lnuB; however, their precise resistance mechanisms remain unclear due to limited sample availability. Six distinct tet genes were identified, with tetM and tetO encoding ribosomal protection proteins that confer tetracycline resistance (30). Additionally, some strains carried the SAT-4 gene, which confers resistance to nucleoside antibiotics. While intrapartum antibiotic prophylaxis primarily targets early-onset GBS disease, the resistance profiles of GBS isolates continue to evolve, with increasing resistance to beta-lactams, erythromycin, and clindamycin, alongside emerging vancomycin-resistant strains (31). Comprehensive characterization of resistance gene distribution provides valuable insights into GBS resistance patterns, thereby informing the development of effective prevention and treatment strategies.

CONCLUSIONS

This study provides a comprehensive genomic characterization of Streptococcus agalactiae (GBS) in China, encompassing serotype distribution, virulence factors, and antimicrobial resistance determinants. While the serotype distribution in China generally aligns with global patterns, significant regional variations exist that warrant further investigation. This research contributes essential knowledge for developing effective prevention and treatment strategies for GBS infections in China. Future studies should focus on more detailed regional and temporal analyses to inform targeted prevention approaches, treatment protocols, and vaccine development strategies.

Conflict of interest: No conflicts of interest.

Reference (31)

Citation:

[1]	Lancefield RC. A serological differentiation of human and other groups of hemolytic streptococci. J Exp Med 1933;57(4):571 − 95. https://doi.org/10.1084/jem.57.4.571.
[2]	Say L, Chou D, Gemmill A, Tunçalp Ö, Moller AB, Daniels J, et al. Global causes of maternal death: a WHO systematic analysis. Lancet Glob Health 2014;2(6):e323 − 33. https://doi.org/10.1016/s2214-109x(14)70227-x.
[3]	Lawn JE, Bianchi-Jassir F, Russell NJ, Kohli-Lynch M, Tann CJ, Hall J, et al. Group B streptococcal disease worldwide for pregnant women, stillbirths, and children: why, what, and how to undertake estimates? Clin Infect Dis 2017;65(suppl_2):S89-99. http://dx.doi.org/10.1093/cid/cix653.
[4]	Russell NJ, Seale AC, O’Driscoll M, O’Sullivan C, Bianchi-Jassir F, Gonzalez-Guarin J, et al. Maternal colonization with group b Streptococcus and serotype distribution worldwide: systematic review and meta-analyses. Clin Infect Dis 2017;65(suppl_2):S100 − 11. https://doi.org/10.1093/cid/cix658.
[5]	Madrid L, Seale AC, Kohli-Lynch M, Edmond KM, Lawn JE, Heath PT, et al. Infant group b streptococcal disease incidence and serotypes worldwide: systematic review and meta-analyses. Clin Infect Dis 2017;65(suppl_2):S160 − 172. https://doi.org/10.1093/cid/cix656.
[6]	Wang J, Zhang Y, Lin M, Bao JF, Wang GY, Dong RR, et al. Maternal colonization with group B Streptococcus and antibiotic resistance in China: systematic review and meta-analyses. Ann Clin Microbiol Antimicrob 2023;22(1):5. https://doi.org/10.1186/s12941-023-00553-7.
[7]	Francois Watkins LK, McGee L, Schrag SJ, Beall B, Jain JH, Pondo T, et al. Epidemiology of invasive group b streptococcal infections among nonpregnant adults in the united states, 2008-2016. JAMA Intern Med 2019;179(4):479 − 88. https://doi.org/10.1001/jamainternmed.2018.7269.
[8]	Lopes E, Fernandes T, Machado MP, Carriço JA, Melo-Cristino J, Ramirez M, et al. Increasing macrolide resistance among Streptococcus agalactiae causing invasive disease in non-pregnant adults was driven by a single capsular-transformed lineage, Portugal, 2009 to 2015. Euro Surveill 2018;23(21):1700473. https://doi.org/10.2807/1560-7917.Es.2018.23.21.1700473.
[9]	Cox LM, Yamanishi S, Sohn J, Alekseyenko AV, Leung JM, Cho I, et al. Altering the intestinal microbiota during a critical developmental window has lasting metabolic consequences. Cell 2014;158(4):705 − 21. https://doi.org/10.1016/j.cell.2014.05.052.
[10]	Slotved HC, Kong FR, Lambertsen L, Sauer S, Gilbert GL. Serotype IX, a proposed new Streptococcus agalactiae serotype. J Clin Microbiol 2007;45(9):2929 − 36. https://doi.org/10.1128/jcm.00117-07.
[11]	Li XO, Gao W, Jia ZL, Yao KH, Yang JY, Tong JJ, et al. Characterization of group b streptococcus recovered from pregnant women and newborns attending in a hospital in Beijing, China. Infect Drug Resist 2023;16:2549 − 59. https://doi.org/10.2147/idr.S395942.
[12]	Lee CC, Hsu JF, Prasad Janapatla R, Chen CL, Zhou YL, Lien R, et al. Clinical and microbiological characteristics of group b Streptococcus from pregnant women and diseased infants in intrapartum antibiotic prophylaxis era in Taiwan. Sci Rep 2019;9(1):13525. https://doi.org/10.1038/s41598-019-49977-2.
[13]	Sheppard AE, Vaughan A, Jones N, Turner P, Turner C, Efstratiou A, et al. Capsular typing method for Streptococcus agalactiae using whole-genome sequence data. J Clin Microbiol 2016;54(5):1388 − 90. https://doi.org/10.1128/jcm.03142-15.
[14]	Kapatai G, Patel D, Efstratiou A, Chalker VJ. Comparison of molecular serotyping approaches of Streptococcus agalactiae from genomic sequences. BMC Genomics 2017;18(1):429. https://doi.org/10.1186/s12864-017-3820-5.
[15]	Schubert A, Zakikhany K, Schreiner M, Frank R, Spellerberg B, Eikmanns BJ, et al. A fibrinogen receptor from group B Streptococcus interacts with fibrinogen by repetitive units with novel ligand binding sites. Mol Microbiol 2002;46(2):557 − 69. https://doi.org/10.1046/j.1365-2958.2002.03177.x.
[16]	Gutekunst H, Eikmanns BJ, Reinscheid DJ. The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells. Infect Immun 2004;72(6):3495 − 504. https://doi.org/10.1128/iai.72.6.3495-3504.2004.
[17]	Morello E, Mallet A, Konto-Ghiorghi Y, Chaze T, Mistou MY, Oliva G, et al. Evidence for the sialylation of PilA, the PI-2a pilus-associated adhesin of Streptococcus agalactiae strain NEM316. PLoS One 2015;10(9):e0138103. https://doi.org/10.1371/journal.pone.0138103.
[18]	Papasergi S, Brega S, Mistou MY, Firon A, Oxaran V, Dover R, et al. The GBS PI-2a pilus is required for virulence in mice neonates. PLoS One 2011;6(4):e18747. https://doi.org/10.1371/journal.pone.0018747.
[19]	Rosini R, Rinaudo CD, Soriani M, Lauer P, Mora M, Maione D, et al. Identification of novel genomic islands coding for antigenic pilus-like structures in Streptococcus agalactiae. Mol Microbiol 2006;61(1):126 − 41. https://doi.org/10.1111/j.1365-2958.2006.05225.x.
[20]	Mudzana R, Mavenyengwa RT, Gudza-Mugabe M. Analysis of virulence factors and antibiotic resistance genes in group B streptococcus from clinical samples. BMC Infect Dis 2021;21(1):125. https://doi.org/10.1186/s12879-021-05820-6.
[21]	Liu YX, Liu JH. Group B streptococcus: virulence factors and pathogenic mechanism. Microorganisms 2022;10(12):2483. https://doi.org/10.3390/microorganisms10122483.
[22]	Vornhagen J, Quach P, Boldenow E, Merillat S, Whidbey C, Ngo LY, et al. Bacterial hyaluronidase promotes ascending GBS infection and preterm birth. mBio 2016;7(3):e00781 − 16. https://doi.org/10.1128/mBio.00781-16.
[23]	Vornhagen J, Adams Waldorf KM, Rajagopal L. Perinatal Group B streptococcal infections: virulence factors, immunity, and prevention strategies. Trends Microbiol 2017;25(11):919 − 31. https://doi.org/10.1016/j.tim.2017.05.013.
[24]	Wu BQ, Su JZ, Li L, Wu WY, Wu JS, Lu YM, et al. Phenotypic and genetic differences among group B Streptococcus recovered from neonates and pregnant women in Shenzhen, China: 8-year study. BMC Microbiol 2019;19(1):185. https://doi.org/10.1186/s12866-019-1551-2.
[25]	Jerlström PG, Talay SR, Valentin-Weigand P, Timmis KN, Chhatwal GS. Identification of an immunoglobulin A binding motif located in the beta-antigen of the c protein complex of group B streptococci. Infect Immun 1996;64(7):2787 − 93. https://doi.org/10.1128/iai.64.7.2787-2793.1996.
[26]	Ernst CM, Staubitz P, Mishra NN, Yang SJ, Hornig G, Kalbacher H, et al. The bacterial defensin resistance protein MprF consists of separable domains for lipid lysinylation and antimicrobial peptide repulsion. PLoS Pathog 2009;5(11):e1000660. https://doi.org/10.1371/journal.ppat.1000660.
[27]	Caliot E, Firon A, Solgadi A, Trieu-Cuot P, Dramsi S. Lipid lysination by MprF contributes to hemolytic pigment retention in group B Streptococcus. Res Microbiol 2024;175(8):104231. https://doi.org/10.1016/j.resmic.2024.104231.
[28]	Sharkey LKR, Edwards TA, O’Neill AJ. ABC-F proteins mediate antibiotic resistance through ribosomal protection. mBio 2016;7(2):e01975. https://doi.org/10.1128/mBio.01975-15.
[29]	Dinos GP. The macrolide antibiotic renaissance. Br J Pharmacol 2017;174(18):2967 − 83. https://doi.org/10.1111/bph.13936.
[30]	Li PY, Wei Y, Li GQ, Cheng H, Xu ZC, Yu ZJ, et al. Comparison of antimicrobial efficacy of eravacycline and tigecycline against clinical isolates of Streptococcus agalactiae in China: in vitro activity, heteroresistance, and cross-resistance. Microb Pathog 2020;149:104502. https://doi.org/10.1016/j.micpath.2020.104502.
[31]	Hayes K, O’Halloran F, Cotter L. A review of antibiotic resistance in Group B Streptococcus: the story so far. Crit Rev Microbiol 2020;46(3):253 − 69. https://doi.org/10.1080/1040841x.2020.1758626.

Vital Surveillances: Serotype Distribution, Virulence, and Antibiotic Resistance Genomic Characterization of Group B Streptococcus — China, 1998–2024