Prevalence of serotypes, antibiotic resistance and virulence genes of Group BStreptococcusisolated from pregnant women at 35–37 weeks of gestation in Ho Chi Minh City, Vietnam

Abstract

Objective: To analyse the prevalence of serotypes, antibiotic resistance, and virulence genes of Group B Streptococcus (GBS) strains isolated from pregnant women at 35-37 weeks of gestation in Ho Chi Minh City, Vietnam, from January 2022 to January 2023.

Methods: GBS strains were isolated through selective culture methods and confirmed by PCR. Serotyping, virulence gene detection, and antibiotic susceptibility testing were performed using PCR, gel electrophoresis techniques and Kirby-Bauer test.

Results: Totally, 61 GBS isolated from 300 participants have been identified including seven GBS serotypes (Ia, I b, II, III, IV, V, and VI). Serotypes VII, VIII, and IX were not detected in the study population. Antibiotic resistance patterns varied: 13.1% of isolates were fully susceptible, while the majority showed multi-drug resistance, with 34.4% resistant to three antibiotics. Serotype I a demonstrated high susceptibility (35.7%), while serotype III showed extensive resistance, with 87.5% being resistant to at least three antibiotics. All strains are susceptible to vancomycin and β-lactams susceptibility also remained high, but resistance to clindamycin, erythromycin, and tetracycline was high (>65%). The virulence genes scpB, cylB, fbsB, and cfb were highly prevalent (90%-100%), indicating their potential for vaccine and diagnostic development.

Conclusions: Our findings provide valuable insights into GBS serotypes, resistance, and virulence factors, contributing to community monitoring, preventive measures, diagnostics, and vaccine development. However, the limited sample size necessitates further research.

Keywords

Serotype / Antibiotic resistance / Virulence / Pregnancy

Conflict of interest statement

Minh-Hoang Tran reported receiving travel reimbursement from Pfizer Vietnam Ltd and Viatris Vietnam Ltd, speaking fees and grants from Servier Vietnam Ltd and Aguettant Asia Pacific Pte Ltd outside the submitted work.

Funding

The authors received no extramural funding for the study.

Authors’ contributions

T.Anh N.T., H.Phuc N., and T.An D.H. conducted the experimental work, including GBS isolation, antibiotic susceptibility testing, DNA extraction, and PCR analysis. M.Hoang T. performed the statistical analysis. T.Loc L. and Hieu V.Q. analyzed the data and drafted the manuscript. Hieu V.Q. supervised the project and revised the manuscript.

Publisher’s note

The Publisher of the Journal remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Edited by Zhang Q, Lei Y, Pan Y

References

[1] Pietrasanta C, Conti MG. Editorial: Neonatal infections and the developing neonatal immune system: Current evidence and research gaps to fill. Front Pediatr 2023; 11: 1243752. doi: 10.3389/fped.2023.1243752.

[2] Blencowe H, Cousens S, Mullany LC, Lee AC, Kerber K, Wall S, et al. Clean birth and postnatal care practices to reduce neonatal deaths from sepsis and tetanus: A systematic review and Delphi estimation of mortality effect. BMC Public Health 2011; 11(3): S11.

[3] Attia Hussein Mahmoud H, Parekh R, Dhandibhotla S, Sai T, Pradhan A, Alugula S, et al. Insight into neonatal sepsis: An overview. Cureus 2023; 15(9): e45530.

[4] Chen X, He H, Wei H, Chen F, Hu Y. Risk factors for death caused by early onset sepsis in neonates: A retrospective cohort study. BMC Infect Dis 2023; 23(1): 844.

[5] Kim F, Polin RA, Hooven TA. Neonatal sepsis. BMJ 2020; 371: m3672. doi: 10.1136/bmj.m3672.

[6] Smilga AS, Garfinkle J, Ng P, Andersen J, Buckley D, Fehlings D, et al. Neonatal infection in children with cerebral palsy: A registry-based cohort study. Pediatr Neurol 2018; 80: 77-83.

[7] Sewell E, Roberts J, Mukhopadhyay S. Association of infection in neonates and long-term neurodevelopmental outcome. Clin Perinatol 2021; 48(2): 251-261.

[8] Jin HD, Demmler-Harrison GJ, Coats DK, Paysse EA, Bhatt A, Edmond JC, et al. Long-term visual and ocular sequelae in patients with congenital cytomegalovirus infection. Pediatr Infect Dis J 2017; 36(9): 877-882.

[9] Carbone F, Montecucco F, Sahebkar A. Current and emerging treatments for neonatal sepsis. Expert Opin Pharmacother 2020; 21(5): 549-556.

[10] Van Du V, Dung PT, Toan NL, Van Mao C, Bac NT, Van Tong H, et al. Antimicrobial resistance in colonizing group B Streptococcus among pregnant women from a hospital in Vietnam. Sci Rep 2021; 11(1): 20845.

[11] Kumalo A, Gebre B, Shiferaw S, Wolde W, Shonde T. Group B Streptococci recto-vaginal colonization, antimicrobial susceptibility pattern, and associated factors among pregnant women at selected health facilities of Wolaita Sodo Town, Southern Ethiopia. Front Microbiol 2023; 14: 1277928. doi: 10.3389/fmicb.2023.1277928.

[12] Steer PJ, Russell AB, Kochhar S, Cox P, Plumb J, Rao GG. Group B streptococcal disease in the mother and newborn—A review. Eur J Obstet Gynecol Reprod Biol 2020; 252: 526-533.

[13] Braye K, Ferguson J, Davis D, Catling C, Monk A, Foureur M. Effectiveness of intrapartum antibiotic prophylaxis for early-onset group B streptococcal infection: An integrative review. Women Birth 2018; 31(4): 244-253.

[14] McGuire E, Ready D, Ellaby N, Potterill I, Pike R, Hopkins KL, et al. A case of penicillin-resistant group B Streptococcus isolated from a patient in the UK. J Antimicrob Chemother 2025; 80(2): 399-404.

[15] Sati H, Carrara E, Savoldi A, Hansen P, Garlasco J, Campagnaro E, et al. The WHO Bacterial Priority Pathogens List 2024: A prioritisation study to guide research, development, and public health strategies against antimicrobial resistance. Lancet Infect Dis 2025; 25(9): 1033-1043.

[16] 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): 253-269.

[17] Liu G, Zhang W, Lu C. Complete genome sequence of Streptococcus agalactiae GD201008-001, isolated in China from tilapia with meningoencephalitis. J Bacteriol 2012; 194(23): 6653-6653.

[18] de Aguiar EL, Mariano DCB, Viana MVC, Benevides L de J, de Souza Rocha F, de Castro Oliveira L, et al. Complete genome sequence of Streptococcus agalactiae strain GBS85147 serotype of type I a isolated from human oropharynx. Stand Genomic Sci 2016; 11(1): 39.

[19] Sulung F, Nik Zuraina NMN, Singh KKB, Hussin A, Hassan SA. Serotypes, virulence and antimicrobial susceptibility of Group B Streptococci isolated from infections in non-pregnant adults in Malaysia. J Taibah Univ Sci 2023; 17(1): 2241706.

[20] Bianchi-Jassir F, Paul P, To KN, Carreras-Abad C, Seale AC, Jauneikaite E, et al. Systematic review of group B streptococcal capsular types, sequence types and surface proteins as potential vaccine candidates. Vaccine 2020; 38(43): 6682-6694.

[21] Maria Silva M, Alcántara Silva É, Novais Teixeira Oliveira C, Cordeiro Santos ML, Lima Souza C, Freire de Melo F, et al. Distribution and prevalence of serotypes of group B Streptococcus isolated from pregnant women in 30 countries: A systematic review. Matern Fetal Med 2023; 5(2): 97-103.

[22] Megli CJ, Carlin SM, Giacobe EJ, Hillebrand GH, Hooven TA. Virulence and pathogenicity of group B Streptococcus: Virulence factors and their roles in perinatal infection. Virulence 2025; 16(1): 2451173.

[23] Liu Y, Liu J. Group B Streptococcus: Virulence factors and pathogenic mechanism. Microorganisms 2022; 10(12): 2483.

[24] Clinical and Laboratory Standards Institute. M100 | Performance Standards for Antimicrobial Susceptibility Testing. [Online]. Available from: https://clsi.org/shop/standards/m100/. [Accessed on 28 November 2025].

[25] Imperi M, Pataracchia M, Alfarone G, Baldassarri L, Orefici G, Creti R. A multiplex PCR assay for the direct identification of the capsular type (Ia to IX) of Streptococcus agalactiae. J Microbiol Methods 2010; 80(2): 212-214.

[26] Smith TC, Roehl SA, Pillai P, Li S, Marrs CF, Foxman B. Distribution of novel and previously investigated virulence genes in colonizing and invasive isolates of Streptococcus agalactiae. Epidemiol Infect 2007; 135(6): 1046-1054.

[27] Michel JL, Madoff LC, Olson K, Kling DE, Kasper DL, Ausubel FM. Large, identical, tandem repeating units in the C protein alpha antigen gene, bca, of group B streptococci. Proc Natl Acad Sci U S A 1992; 89(21): 10060-10064.

[28] Bobadilla FJ, Novosak MG, Cortese IJ, Delgado OD, Laczeski ME. Prevalence, serotypes and virulence genes of Streptococcus agalactiae isolated from pregnant women with 35-37 weeks of gestation. BMC Infect Dis 2021; 21(1): 73.

[29] Duarte RS, Bellei BC, Miranda OP, Brito MAVP, Teixeira LM. Distribution of antimicrobial resistance and virulence-related genes among Brazilian group B streptococci recovered from bovine and human sources. Antimicrob Agents Chemother 2005; 49(1): 97-103.

[30] Bidet P, Brahimi N, Chalas C, Aujard Y, Bingen E. Molecular characterization of serotype III group B-Streptococcus isolates causing neonatal meningitis. J Infect Dis 2003; 188(8): 1132-1137.

[31] Zhou J, Zhang L, Zhang Y, Liu H, Xu K, Zhang B, et al. Analysis of molecular characteristics of CAMP-negative Streptococcus agalactiae strains. Front Microbiol 2023; 14: 1189093.

[32] Hanh TQ, Van Du V, Hien PT, Chinh DD, Loi CB, Dung NM, et al. Prevalence and capsular type distribution of group B Streptococcus isolated from vagina of pregnant women in Nghe An province, Vietnam. Iran J Microbiol 2020; 12(1): 11-17.

[33] Turner C, Turner P, Po L, Maner N, De Zoysa A, Afshar B, et al. Group B streptococcal carriage, serotype distribution and antibiotic susceptibilities in pregnant women at the time of delivery in a refugee population on the Thai-Myanmar border. BMC Infect Dis 2012; 12(1): 34.

[34] Eskandarian N, Ismail Z, Neela V, van Belkum A, Desa MNM, Amin Nordin S. Antimicrobial susceptibility profiles, serotype distribution and virulence determinants among invasive, non-invasive and colonizing Streptococcus agalactiae (group B Streptococcus) from Malaysian patients. Eur J Clin Microbiol Infect Dis 2015; 34(3): 579-584.

[35] Cheng Z, Qu P, Ke P, Yang X, Zhou Q, Lan K, et al. Antibiotic resistance and molecular epidemiological characteristics of Streptococcus agalactiae isolated from pregnant women in Guangzhou, South China. Can J Infect Dis Med Microbiol 2020; 2020: 1368942. doi: 10.1155/2020/1368942.

[36] Safari D, Gultom SM, Tafroji W, Azzahidah A, Soesanti F, Khoeri MM, et al. Prevalence, serotype and antibiotic susceptibility of Group B Streptococcus isolated from pregnant women in Jakarta, Indonesia. PLoS One 2021; 16(5): e0252328.

[37] Wang J, Zhang Y, Lin M, Bao J, Wang G, Dong R, et al. Maternal colonization with group B Streptococcus and antibiotic resistance in China: Systematic review and meta-analyses. Ann Clin Microbiol 2023; 22(1): 5.

[38] No authors listed. Prevention of group B Streptococcal early-onset disease in newborns: ACOG Committee opinion, Number 797. Obstet Gynecol 2020; 135(2): 489-492.

[39] Puopolo KM, Lynfield R, Cummings JJ, Hand I, et al; Committee on Fetus and Newborn, Committee on Infectious Diseases. Management of infants at risk for group B streptococcal disease. Pediatrics 2019; 144(2): e20191881.

[40] Filkins L, Hauser JR, Robinson-Dunn B, Tibbetts R, Boyanton BL, Revell P. American Society for Microbiology provides 2020 guidelines for detection and identification of group B Streptococcus. J Clin Microbiol 2020; 59(1): e01230-20.

[41] Dore N, Bennett D, Kaliszer M, Cafferkey M, Smyth CJ. Molecular epidemiology of group B streptococci in Ireland: Associations between serotype, invasive status and presence of genes encoding putative virulence factors. Epidemiol Infect 2003; 131(2): 823-833.

[42] Manning SD, Ki M, Marrs CF, Kugeler KJ, Borchardt SM, Baker CJ, et al. The frequency of genes encoding three putative group B streptococcal virulence factors among invasive and colonizing isolates. BMC Infect Dis 2006; 6: 116.

[43] 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.

[44] Jiang H, Chen M, Li T, Liu H, Gong Y, Li M. Molecular characterization of Streptococcus agalactiae causing community- and hospital-acquired infections in Shanghai, China. Front Microbiol 2016; 7: 1308.

[45] Bahez A, Mahmud MIA-DM, Hamzah HA, Wahid HH. Virulence-genes Rib and Bca in serotypes of group B Streptococcus (GBS) isolated from symptomatic pregnant women in East Coast Malaysia. IIUM Med J Malay 2021; 20(3): 118-126. doi: 10.31436/imjm.v20i3.1633.

[46] Eliza M, Kalinka J, Bigos M, Prosniewska M, Wasiela M. Occurrence of virulence genes among Sagalactiae isolates from vagina and anus of pregnant women-a pilot study. Arch Perinat Med 2011; 17(4): 229-234.

[47] Udo EE, Boswihi SS, Al-Sweih N. Genotypes and virulence genes in Group B Streptococcus isolated in the Maternity Hospital, Kuwait. Med Princ Pract 2013; 22(5): 453-457.

[48] Mohamed Sadaka S, Abdelsalam Aly H, Ahmed Meheissen M, Orief YI, Mohamed Arafa B. Group B streptococcal carriage, antimicrobial susceptibility, and virulence related genes among pregnant women in Alexandria, Egypt. Alex J Med 2018; 54(1): 69-76.

[49] Thwe PM, Faron ML, Pride DT, Cruz A, Gerstbrein D, Nahmod KA, et al. Multicenter evaluation of the Cepheid Xpert GBS LB XC test. J Clin Microbiol 2022; 60(12): e0135622.

[50] Creti R, Imperi M, Stanziale A, Giuliani G, Fazii P, Savini V. Group B streptococci (GBS) strains evading molecular diagnostics showed novel chromosomal deletions encompassing the CAMP-factor (cfb) encoding gene. Eur J Clin Microbiol Infect Dis 2023; 42(7): 913-916.