Edited by: Cheng-Hsun Chiu, Chang Gung Children's Hospital, Taiwan
Reviewed by: Chienchung Lee, Linkou Chang Gung Memorial Hospital, Taiwan; Sergio Eduardo Longo Fracalanzza, Federal University of Rio de Janeiro, Brazil
This article was submitted to Pediatric Infectious Diseases, a section of the journal Frontiers in Pediatrics
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Group B
To date, there are 10 known GBS serotypes (Ia, Ib, and II-IX) that are categorized based on capsular polysaccharide (CPS) composition (
This study was approved by the Ethics Committee of the Women and Children's Hospital, Xiamen University (Xiamen, China). All participants or their guardians provided written informed consent before enrolling in this study. A total of 3,452 pregnant women with GBS colonization during late pregnancy (35–37 weeks gestation) were admitted to our hospital for labor between June 2016 and June 2018, while 228 cases were excluded according to our study criteria (
Flow chart of case and control enrollment and selection.
We then statistically calculated the sample size. GBS colonization rate of pregnant women in our hospital was 14.5% based on a previous study (
Pregnant women at 35–37 weeks of gestation submitted samples for GBS bacterial culture collected by swabbing both the lower vagina and rectum (through the anal sphincter) into the plastic TranSwab device (Qi Xing Biotechnology Company, Suzhou, China). The swabs were then cultured in the plastic tube at 35°C in an incubator containing 5% CO2 for 24–48 h. The chromogenic agar in the tube undergoes color change in the presence of β-hemolytic GBS colonies. The positive tubes were then selected and cultured in a Colombian blood agar plate (Beiruite Biotechnology Co. Ltd., Zhengzhou, China) for further bacterial identification and determination of the GBS strains using the American PHOENIX100 bacterial identification system (Becton and Dickinson Company, Franklin Lake, NJ, USA). Tracheal secretion, blood samples, and the cerebrospinal fluid were also collected from neonates born to the enrolled pregnant women, who were subsequently admitted into the neonatal ward, and subjected to the GBS detection. All strains were stored in a −80°C freezer.
All 298 strains from mothers and 32 strains from neonates were confirmed as having GBS, and the isolates were serotyped using the latex agglutination kits for GBS Ia, Ib, and II–IX (Statens Serum Institut, Copenhagen, Denmark) according to the manufacturer's protocols. The isolate was defined as non-typeable (NT) when it could not be categorized into any serotype (
Chromosomal DNA was extracted from overnight cultures of the isolates at 35°C on 5% Müeller-Hinton agar using a DNA Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions. The DNA samples were then subjected to PCR-amplification of seven housekeeping genes (
SPSS statistics for Windows, Version 25.0 (IBM Corp., Armonk, NY, USA) was used to statistically analyze our data. The qualitative variables were compared using the chi-square or Fisher's exact test, while the correlation analysis was presented by the coefficient of the contingency. Analysis of multiple sample rates was performed using the
Among the 298 GBS isolates, we obtained 266 strains of GBS in the pregnant women without GBS-EOD neonates and 32 GBS strains with GBS-EOD neonates. We also found that these 32 mothers and their offsprings with GBS-EOD had the same GBS strains, including the same serotype and genotype. There were 8 serotypes among 266 GBS isolates. The most predominant serotype was III, accounting for 54.9% (146/266) of all isolates, followed by Ib [17.3% (46/266)], V [10.1% (27/266)], Ia [9.4% (25/266)], II [4.9% (13/266)], NT [1.0% (3/266)], VI [0.8% (2/266)], VIII [0.8% (2/266)], and IX [0.8% (2/266)].
There were a total of 42 STs identified among these 266 GBS isolates and ST19 was the most prevalent type [19.9% (53/266)], followed by ST862 [9.4% (25/266)], ST12 [7.9% (21/266)], ST17 [7.5% (20/266)], ST10 [7.1% (19/266)], ST23 [4.9% (13/266)], ST131 [4.1% (11/266)], and ST651 [3.8% (10/266)]. The remaining 34 genotypes were a single digit, and six strains were undetermined.
Furthermore, the main genotype of the serotype Ia was ST23 [28.0% (7/25)], while serotype Ib was dominated by ST12 [41.3% (19/46)] and ST10 [28.3% (13/46)], and serotype III was mainly comprised of ST19 [30.8% (45/146)] and ST17 [13.7% (20/146)]. We also observed unusual associations among these serotypes; serotype Ia with ST4 [16.0% (4/25)] and ST221 [16.0% (4/25)], serotype Ib with ST339 [6.5% (3/46)], and serotype III with ST862 [15.1% (22/146)] and ST862 [6.8% (10/146)]. However, the main serotype of ST17, ST19, ST131, ST651, and ST862 was serotype III [100.0% (20/20), 84.9% (45/53), 90.9% (10/11), 90.0% (9/10), and 88.0% (22/25), respectively], while ST10 and ST12 were associated with serotype Ib [73.7% (14/19) and 90.5% (19/21)], ST23 was associated with serotype Ia [53.8% (7/13)], and ST1 was associated with serotype V [62.5% (5/8)].
There were a total of five serotypes in the 32 cases of neonatal GBS-EOD. We identified 18 strains (56.3%) as serotype III, 8 strains (25.0%) as serotype Ia, 3 strains (9.4%) as serotype Ib, 2 strains (6.2%) as serotype II, and 1 strain (3.1%) as serotype V.
The DNA ST analysis revealed 10 STs among these 32 GBS isolates. ST17 was the most prevalent type [43.8% (14/32)], followed by ST23 [18.8% (6/32)], ST19 [12.5% (4/32)], and ST12 [6.3% (2/32)]. However, other genotypes, such as ST1, ST10, ST24, ST27, ST131, and ST651, were also identified, but there was only one isolate detected for each ST [all 3.1% (1/32)].
In these 32 cases of neonatal GBS-EOD, the top three serotypes were III, Ia, and Ib. The dominant and most prevalent genotype of serotype III was ST17 [72.2 % (13/18)]; the dominant genotype with the second most prevalent serotype Ia was ST23 [87.5% (6/8)]; and the dominant genotype with the third most prevalent serotype Ib was ST12 [66.7% (2/3)]. With regard to genotypes, the top three were ST17, ST23, and ST19 in these 32 cases of neonatal GBS-EOD. The dominant and most prevalent serotype of ST17 was III [92.9% (13/14)]; the second most prevalent serotype of ST23 was Ia, and the third more prevalent serotype of ST19 was III (
Genetic diversity of five GBS serotypes in 32 strains of neonatal GBS-EOD.
Ia | 8 | 1 | 0 | 0 | 0 | 0 | 6 | 0 | 0 | 0 | 1 |
Ib | 3 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
II | 2 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
III | 18 | 0 | 0 | 0 | 13 | 4 | 0 | 0 | 1 | 0 | 0 |
V | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
There were only three types of clinical diagnoses in the 32 cases of neonatal GBS-EOD, including 13 cases of pneumonia (one death with serotype Ia and ST23), 14 cases of sepsis, and 5 cases of meningitis (one death with serotype III and ST17). These were the main clinical diagnoses rather than including only diagnosis based on clinical manifestations. Among these pneumonia, sepsis, and meningitis diagnoses, serotype III was the main GBS type, accounting for 46.2% (6/13), 50% (7/14), and 100% (5/5), respectively, although there was no statistically significant difference in distribution of the five GBS serotypes in these three diagnoses in GBS-EOD (
Serotype distribution of 32 GBS-EOD cases with pneumonia, sepsis, and meningitis [
Pneumonia | 13 | 3 (23.1) | 2 (15.4) | 1 (7.7) | 6 (46.1) | 1 (7.7) |
Sepsis | 14 | 5 (35.7) | 1 (7.1) | 1 (7.1) | 7 (50.0) | 0 (0) |
Meningitis | 5 | 0 (0) | 0 (0) | 0 (0) | 5 (100.0) | 0 (0) |
χ2-value | – | |||||
0.654 |
Genotype distribution of 32 GBS-EOD cases with pneumonia, sepsis, and meningitis [
Pneumonia | 13 | 1 (7.7) | 0 (0) | 0 (0) | 5 (38.4) | 2 (15.4) | 2 (15.4) | 0 (0) | 1 (7.7) | 1 (7.7) | 1 (7.7) |
Sepsis | 14 | 0 (0) | 1 (7.1) | 1 (7.1) | 5 (35.7) | 2 (14.4) | 4 (28.6) | 1 (7.1) | 0 (0) | 0 (0) | 0 (0) |
Meningitis | 5 | 0 (0) | 0 (0) | 1 (20.0) | 4 (80.0) | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0 (0) |
χ2-value | – | ||||||||||
0.752 |
This cohort of patients and neonatal GBS-EOD was divided into case and control groups according to the groups of pregnant women with and without GBS-EOD neonates. We then compared GBS serotypes between these two groups (
Association of vertical transmission of GBS serotypes between case and control groups.
Case group | 32 | 8 (2.7) |
3 (−1.1) | 2 (0.3) | 18 (0.1) | 1 (−1.7) | ||||
Control group | 266 | 25 (−2.7) | 46 (1.1) | 13 (−0.3) | 146 (−0.1) | 36 (1.7) | ||||
χ2-value | – | |||||||||
0.046 |
Association of vertical transmission of GBS genotypes between case and control groups.
Case | 32 | 1 (0.0) |
1 (−0.9) | 2 (−0.3) | 14 (6.1) | 4 (−1.0) | 6 (3.0) | 1 (0.3) | 1 (0.2) | 1 (−0.3) | 1 (−0.2) | 0 (−4.2) |
Control | 266 | 8 (0.0) | 19 (0.9) | 21 (0.3) | 20 (−6.1) | 53 (1.0) | 13 (−3.0) | 6 (−0.3) | 7 (−0.2) | 11 (0.3) | 10 (0.2) | 98 (4.2) |
χ2-value | 51.34 | |||||||||||
0.000 |
In the current study, we found that serotype III was the most commonly distributed serotype in 266 GBS strains in pregnant women without GBS-EOD cases, accounting for 54.9%, followed by Ib, V, and Ia. A previous multicenter study in Shanghai showed that GBS serotypes III, V, and Ia were the most important serotypes in pregnant women with GBS colonization, accounting for 79.7% (
Our current study also assessed the genotype distributions of 266 GBS strains isolated from pregnant women and identified a total of 42 STs and 6 undetermined (UD) STs, with ST19 being the most prevalent (19.9%), followed by ST862, ST12, ST17, ST10, ST23, ST131, and ST651. Among these, ST1, ST17, ST19, and ST23 accounted for 35.3% of total GBS genotypes, which was inconsistent with that of a previous Canadian study reporting only 66.7% (
Interestingly, our current study also showed that serotypes III and Ia were the predominant serotypes in the 32 GBS strains in neonatal GBS-EOD, accounting for 81.3% of all serotypes. This indicates that these two serotypes may possess the strongest virulence for GBS-EOD. Indeed, a previous study revealed that GBS serotypes III and Ia were more virulent in causing GBS maternal colonization or infection and neonatal morbidity for 50% of the cases (
In addition, our current study revealed an association of GBS serotypes between pregnant women and neonatal GBS-EOD with an adjusted standardized residual of serotype Ia as 2.7 (>2) and serotype III as 0.1, while the vaginal colonization of serotype III was the most common (55.0%) and the vertical transmission rate was low, consistent with previous studies (
Our current study was retrospective and contained a limited number of study subjects. Specifically, we only included GBS-EOD cases and we had a limited study population from only one medical center and one regional hospital in Xiamen, China.
In summary, our current data demonstrated that there is an association of GBS serotype Ia and genotypes ST17 and ST23 colonized in late pregnancy and GBS-EOD in neonates. The ST23 of serotype Ia and ST17 of serotype III possessed a strong hypervirulence to cause GBS-EOD. Further studies are needed to confirm the application of these GBS serotypes and genotypes for future treatment and development of vaccinations against GBS infection and colonization.
All datasets generated for this study are included in the article.
This study was approved by the Ethics Committee of the Women and Children's Hospital, Xiamen University (Xiamen, China). All participants or their guardians provided written informed consent before enrolling in this study.
LX and CC conceptualized and designed the study, reviewed, and revised the manuscript. ZY searched the literature, performed the data analyses, and prepared the manuscript. WJ, ZX, and CL carried out experiments and analyzed experimental data. HM, MS, and LY collected data. All authors read and approved the final version of the manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We would like to thank all staff members for participation in and contribution to this study. We also thank the study participants for providing the samples and Shenzhen Huada Gene Technology Co. Ltd. for DNA sequencing of our isolates. The