Multicenter study evaluating performance of the Smart Group B Streptococcus (GBS) assay using an enrichment protocol for detecting GBS colonization in patients in the antepartum period

Quantitative real-time PCR and magnetic separation strategy for specific detection of group B streptococcus in perinatal Women's urine

Introduction

Group B streptococcus(GBS)often causes adverse outcomes such as urinary system infection, intrauterine infection, premature birth, and stillbirth in perinatal women. Perinatal screening of GBS is conducive to guiding clinical scientific intervention and improving delivery outcomes.This study quantitative real-time PCR (RT-qPCR) combined with magnetic separation was used for GBS detection.

Materials and methods

Sample pre-treatment in this study involved the utilization of magnetic separation (MS) technology, aiming to expedite the detection process and enhance detection sensitivity, and the cfb gene of group B streptococcus was used as the target gene to establish quantitative real-time PCR (RT-qPCR) to detect group B streptococcus.

Results

It was found that penicillin-functionalized magnetic beads had a good ability to enrich and capture group B Streptococcus.The findings revealed an exceptional detection sensitivity, with the ability to detect B streptococcus in urine samples at levels as low as 102 CFU/mL.

Conclusions

The utilization of MS technology in conjunction with the RT-qPCR (MS-RT-qPCR) assay, as demonstrated in this study, offers a viable approach for prenatal screening of group B streptococcus among perinatal women.

Use of Recombinant Endolysin to Improve Accuracy of Group B Streptococcus Tests

Group B Streptococcus (GBS) causes serious neonatal infection via vertical transmission. The prenatal GBS screening test is performed at the late stage of pregnancy to avoid risks of infection. In this test, enrichment culture is performed, followed by GBS identification. Selective medium is used for the enrichment; however, Enterococcus faecalis, which is a potential contaminant in swab samples, can interfere with the growth of GBS. Such bacterial contamination can lead to false-negative results. Endolysin, a bacteriophage-derived enzyme, degrades peptidoglycan in the bacterial cell wall; it is a promising antimicrobial agent for selectively eliminating specific bacterial genera/species. In this study, we used the recombinant endolysin EG-LYS, which is specific to E. faecalis; the endolysin potentially enriched GBS in the selective culture. First, in the false-negative model (coculture of GBS and E. faecalis, which disabled GBS detection in the subsequent GBS identification test), EG-LYS treatment at 0.1 mg/ml improved GBS detection. Next, we used 548 vaginal swabs to test the efficacy of EG-LYS treatment in improving GBS detection. EG-LYS treatment (0.1 mg/ml) increased the GBS-positive ratio to 17.9%, compared to 15.7% in the control (phosphate-buffered saline [PBS] treatment). In addition, there were an increased number of GBS colonies under EG-LYS treatment in some samples. The results were supported by the microbiota analysis of the enriched cultures. In conclusion, EG-LYS treatment of the enrichment culture potentially improves the accuracy of the prenatal GBS screening test. IMPORTANCE Endolysin is a bacteriophage-derived enzyme that degrades the peptidoglycan in the cell wall of host bacteria; it could be used as an antimicrobial agent for selectively eliminating specific bacterial genera/species. Group B Streptococcus (GBS) causes neonatal infection via vertical transmission; prenatal GBS screening test, in which enrichment culture is followed by bacterial identification, is used to detect the presence of GBS in pregnant women. However, the presence of commensal bacteria such as Enterococcus faecalis in clinical specimens can inhibit GBS growth in the selective enrichment culture, resulting in false-negative result. Here, we demonstrated that the application of originally isolated endolysin in the enrichment culture improved the test accuracy by inhibiting unwanted E. faecalis growth and therefore avoiding false-negative results, not only in experimental settings, but also in tests using vaginal swabs.

The effect of group B streptococcus on maternal and infants' prognosis in Guizhou, China

Group B Streptococcus (GBS) is a kind of opportunistic pathogenic bacteria and mainly strikes the lower digestive tract and genitourinary tract. It is a major risk factor for neonatal babies, seriously threatening their lives. In the present study, we aimed to detect the GBS colonization in late pregnant women, and to study the effect of GBS on maternal and infants’ prognosis. Pregnant women with a gestational age of 35–37 weeks were enrolled in the study. Real-time polymerase chain-reaction (RT-PCR) was used to detect the colonization of GBS in the vaginal and rectal secretions for late pregnant women according to the screening guidelines. Chi-square test was applied to analyze the relationship between GBS colonization and clinical characteristics. A follow-up of 6 weeks was performed on the puerpera and infants after delivery. The positive rate of GBS was 12.6% in late pregnant women. GBS carrier state was positively related to several pregnancy outcomes, including intrauterine infection, premature rupture of membranes, postpartum hemorrhage, fetal distress and puerperal infection, as well as to part neonatal outcomes, containing neonatal infection, neonatal pneumonia and neonatal sepsis (all P < 0.05). GBS infection in late pregnant women results in adverse effects on maternal and neonatal outcomes.

Comparison of qPCR and culture methods for group B Streptococcus colonization detection in pregnant women: evaluation of a new qPCR assay

BACKGROUND

Streptococcus Group B (GBS) colonization in pregnant women is the most important risk factor for newborn disease due to vertical transmission during delivery. GBS colonization during pregnancy has been implicated as a leading cause of perinatal infections. Traditionally, pregnant women are screened for GBS between 35 and 37 weeks of gestation. However, antenatal culture-based screening yields no information on GBS colonization status and offers low predictive value for GBS colonization at delivery. Numerous assays have been evaluated for GBS screening in an attempt to validate a fast and efficient method. The aim of this study was to compare bacteria isolation by culture and two qPCR techniques, targeting sip and cfb genes, respectively, for detecting colonizing GBS.

METHODS

Cultures - the gold-standard technique, a previous qPCR technique targeting the sip gene, and a new proposed qPCR assay targeting the cfb gene were evaluated as diagnostic tools on 320 samples.

RESULTS

Considering cultures as the gold standard, the evaluated qPCR method detected 75 out of 78 samples, representing a sensitivity of 93.58% (95% confidence interval (CI), 90.89-96.27) and specificity of 94.62% (95% CI, 91.78-97.46). However, an additional analysis was performed for true positives that included not only samples showing positives by culture but samples showing positive for both qPCR assays. The sensitivity and specificity were recalculated including these discrepant samples and a total of 89 samples were considered as positive, giving a prevalence of 27.81%. With this new analysis, the qPCR targeting the cfb gene showed a sensitivity of 95.5% (95% CI, 88.65-98.59) and specificity of 99.13% (95% CI, 96.69-99.97).

CONCLUSIONS

The new qPCR method is a sensitive and specific assay for detecting GBS colonization and represents a valuable tool for identifying candidates for intrapartum antibiotic prophylaxis. Cultures should be retained as the reference and the routine technique because of its specificity and cost analysis ratio, but it would be convenient to introduce PCR techniques to check negative culture samples or when an urgent detection is required to reduce risk of infection among infants.

Rapid detection of Group B streptococcus directly from vaginal-rectal specimens using liquid swabs and the BD Max GBS assay

OBJECTIVE

We adapted the BD Max GBS assay, an automated platform for the detection of Group B streptococcus (GBS) DNA in vaginal-rectal swab specimens after LIM broth enrichment, to directly detect GBS in specimens collected using cellular foam swabs in Amies liquid medium. We compared the BD Max GBS assay performance to that of enriched culture and the BD GeneOhm StrepB assay.

METHODS

Seventy-two reference vaginal-rectal specimens were employed to determine the limit of GBS detection and the preferred test volume for direct detection of GBS. A total of 304 clinical specimens were then tested by the optimized BD Max GBS assay, both by direct testing and following broth enrichment.

RESULTS

The limit of GBS detection was 75 CFU/mL and the preferred test volume was 100 μL. Of 304 clinical specimens tested, GBS was detected in 62 specimens by enriched culture (20.4%); 61 of these yielded GBS by the BD Max GBS assay when performed directly from the liquid swab (sensitivity 98.4%). All 242 culture-negative specimens also yielded negative results by the BD Max GBS assay (specificity 100%). When this assay was performed following broth enrichment, GBS was detected in all 62 culture-positive specimens (100% sensitivity). The sensitivity and specificity of the BD GeneOhm StrepB assay was 90.3% and 99%, respectively.

CONCLUSIONS

The BD Max GBS assay is highly sensitive, requires minimal technical skill with <2 min required to set-up, and results are available in under 80 min (versus 24-48 h for culture). It is configured for 'on demand' testing and vaginal-rectal specimens can be rapidly screened for GBS without the need for enrichment. The results obtained in this study demonstrate that rapid GBS screening using the BD Max GBS assay at the time of delivery is a viable alternative to the current recommended screening at 35-37 weeks of gestation with pre-enrichment testing methods.

Visualization of the role of host heme on the virulence of the heme auxotroph Streptococcus agalactiae

Heme is essential for several cellular key functions but is also toxic. Whereas most bacterial pathogens utilize heme as a metabolic cofactor and iron source, the impact of host heme during bacterial infection remains elusive. The opportunist pathogen Streptococcus agalactiae does not synthesize heme but still uses it to activate a respiration metabolism. Concomitantly, heme toxicity is mainly controlled by the HrtBA efflux transporter. Here we investigate how S. agalactiae manages heme toxicity versus benefits in the living host. Using bioluminescent bacteria and heme-responsive reporters for in vivo imaging, we show that the capacity of S. agalactiae to overcome heme toxicity is required for successful infection, particularly in blood-rich organs. Host heme is simultaneously required, as visualized by a generalized infection defect of a respiration-negative mutant. In S. agalactiae, HrtBA expression responds to an intracellular heme signal via activation of the two-component system HssRS. A hssRS promoter-driven intracellular luminescent heme sensor was designed to identify host compartments that supply S. agalactiae with heme. S. agalactiae acquires heme in heart, kidneys, and liver, but not in the brain. We conclude that S. agalactiae response to heme is organ-dependent, and its efflux may be particularly relevant in late stages of infection.

Prevalence of maternal colonisation with group B streptococcus: a systematic review and meta-analysis

BACKGROUND

The most important risk factor for early-onset (babies younger than 7 days) invasive group B streptococcal disease is rectovaginal colonisation of the mother at delivery. We aimed to assess whether differences in colonisation drive regional differences in the incidence of early-onset invasive disease.

METHODS

We did a systematic review of maternal group B streptococcus colonisation studies by searching MEDLINE, Embase, Pascal Biomed, WHOLIS, and African Index Medicus databases for studies published between January, 1997, and March 31, 2015, that reported the prevalence of group B streptococcus colonisation in pregnant women. We also reviewed reference lists of selected studies and contacted experts to identify additional studies. Prospective studies in which swabs were collected from pregnant women according to US Centers for Disease Control and Prevention guidelines that used selective culture methods were included in the analyses. We calculated mean prevalence estimates (with 95% CIs) of maternal colonisation across studies, by WHO region. We assessed heterogeneity using the I(2) statistic and the Cochran Q test.

FINDINGS

221 full-text articles were assessed, of which 78 studies that included 73 791 pregnant women across 37 countries met prespecified inclusion criteria. The estimated mean prevalence of rectovaginal group B streptococcus colonisation was 17·9% (95% CI 16·2-19·7) overall and was highest in Africa (22·4, 18·1-26·7) followed by the Americas (19·7, 16·7-22·7) and Europe (19·0, 16·1-22·0). Studies from southeast Asia had the lowest estimated mean prevalence (11·1%, 95% CI 6·8-15·3). Significant heterogeneity was noted across and within regions (all p≤0·005). Differences in the timing of specimen collection in pregnancy, selective culture methods, and study sample size did not explain the heterogeneity.

INTERPRETATION

The country and regional heterogeneity in maternal group B streptococcus colonisation is unlikely to completely explain geographical variation in early-onset invasive disease incidence. The contribution of sociodemographic, clinical risk factor, and population differences in natural immunity need further investigation to understand these regional differences in group B streptococcus maternal colonisation and early-onset disease.

FUNDING

None.

Bacterial Infections

Molecular techniques have revolutionized the detection and identification of microorganisms. Real-time PCR has allowed for the rapid and accurate detection of MRSA, VRE, and group B Streptococcus. The identification of difficult and slow-growing organisms has been expedited by sequence-based methods such as 16S rRNA gene sequencing. Rapid identification of organisms and detection of resistance markers directly from positive blood culture bottles has become a reality. Finally, a transformation is taking place with the introduction of MALDI-TOF into clinical laboratories that promises to improve the accuracy and speed of bacterial and fungal identifications by days. The advantages of these methodologies and their associated clinical applications, along with their inherent pitfalls and problems, are elucidated in this chapter.

Isothermal Recombinase Polymerase Amplification Assay Applied to the Detection of Group B Streptococci in Vaginal/Anal Samples

BACKGROUND

Group B streptococcal infections are the leading cause of sepsis and meningitis in newborns. A rapid and reliable method for the detection of this pathogen at the time of delivery is needed for the early treatment of neonates. Isothermal amplification techniques such as recombinase polymerase amplification have advantages relative to PCR in terms of the speed of reaction and simplicity.

METHODS

We studied the clinical performance of recombinase polymerase amplification for the screening of group B streptococci in vaginal/anal samples from 50 pregnant women. We also compared the limit of detection and the analytical specificity of this isothermal assay to real-time PCR (RT-PCR).

RESULTS

Compared to RT-PCR, the recombinase polymerase amplification assay showed a clinical sensitivity of 96% and a clinical specificity of 100%. The limit of detection was 98 genome copies and the analytical specificity was 100% for a panel of 15 bacterial and/or fungal strains naturally found in the vaginal/anal flora. Time-to-result for the recombinase polymerase amplification assay was &lt;20 min compared to 45 min for the RT-PCR assay; a positive sample could be detected as early as 8 min.

CONCLUSIONS

We demonstrate the potential of isothermal recombinase polymerase amplification assay as a clinically useful molecular diagnostic tool that is simple and faster than PCR/RT-PCR. Recombinase polymerase amplification offers great potential for nucleic acid–based diagnostics at the point of care.

Evaluation of Culture, Antigen Detection and Polymerase Chain Reaction for Detection of Vaginal Colonization of Group B Streptococcus (GBS) in Pregnant Women

BACKGROUND AND OBJECTIVE

Group B Streptococcal infection is an important cause of neonatal morbidity and mortality. Early detection of perinatal vagino-rectal (VR) carriage of Group B Streptococcus (GBS) is important in the management of newborn infections. The objective of the study was to evaluate Culture, antigen detection and Polymerase chain reaction for detection of GBS in Pregnant women.

SETTINGS AND DESIGN

Observational descriptive study was done in a tertiary care hospital in Southern India.

MATERIALS AND METHODS

VR swabs were collected from 50 women at 35 to 37 weeks of gestation. Culture in a selective Lim enrichment broth with subsequent culture on 5% sheep blood agar, Conventional PCR assay and antigen detection method were performed. The performance of antigen detection and PCR methods were compared with culture.

STATISTICAL ANALYSIS

STATISTICAL ANALYSIS was performed by Chi-Square test.

RESULTS

GBS cultures were positive for 16% of the specimen (8 out of 50). Considering culture as a gold standard, Sensitivity, Specificity, Positive predictive value and Negative predictive value of antigen detection was 100%, 92.86%, 72.73%, 100% and similarly for that of PCR was 100%, 45.23%, 25.80%, 100%, respectively.

CONCLUSION

Antigen detection method was the rapid, sensitive and specific test for the detection of GBS colonizers during pregnancy.

Evaluation of the new brilliance GBS chromogenic medium for screening of Streptococcus agalactiae vaginal colonization in pregnant women

Three commercial chromogenic agar media were evaluated for Streptococcus agalactiae screening in 200 vaginal swabs from pregnant women. The sensitivity and specificity were 94.3% and 100% for Granada medium (bioMérieux), 100% and 90.3% for Brilliance GBS medium (Thermo Fisher Scientific), and 100% and 98.8% for ChromID STRB medium (bioMérieux), respectively.

Culture-based method with performance comparable to that of PCR-based methods for detection of group B Streptococcus in screening samples from pregnant women

We compared five approaches for group B streptococcus (GBS) detection: three culture-based methods and two methods using broth-enhanced real-time PCR. Carrot broth-enhanced subculture to GBS Detect (Hardy Diagnostics, Santa Maria, CA) exhibited sensitivity and specificity comparable to carrot broth- and LIM broth-enhanced real-time PCRs.

Usefulness of a rapid real-time PCR assay in prenatal screening for group B streptococcus colonization

Background

Group B streptococcus (GBS) infection is a leading cause of neonatal morbidity and mortality worldwide. Here, we present the analytical and diagnostic usefulness of a new real-time PCR-based assay (Xpert GBS; Cepheid, USA) for rapid and accurate prenatal GBS screening.

Methods

We enrolled 175 pregnant women who were between 35 and 39 weeks of gestation. The analytical performance of the Xpert GBS assay was first tested using a reference GBS strain. Next, to test diagnostic performance, rectovaginal swabs were obtained from pregnant women who visited the hospital for regular antenatal screening after 34 weeks of gestation. The results of the Xpert GBS assay were compared to those of standard culture for the detection of prenatal GBS colonization.

Results

When any positive result from Xpert GBS or culture was considered a true positive, the sensitivity of the Xpert GBS assay and culture were 91% (20/22; 95% CI [confidence interval], 72-98) and 68% (15/22; 95% CI, 47-84), respectively. The specificity of both methods was 100% (153/153; 95% CI, 97-100). The sensitivity and specificity of the Xpert GBS assay, using the culture results as a reference, were 86.7% and 95.6%, respectively. In the Xpert GBS assay, the median threshold cycle of vaginally colonized samples was significantly lower than rectally colonized samples (P<0.01).

Conclusions

The Xpert GBS assay is an accurate, rapid, easy-to-use test for the detection of maternal GBS colonization in prenatal screening that might be especially useful in clinical settings where standard culture is not feasible.

Optimization of a rapid diagnostic test for detection of group B streptococcus from antepartum patients

We analyzed the performance of a new rapid diagnostic test for use in determining group B streptococcus colonization in pregnancy. Vaginal-rectal specimens were compared by the rapid test, a commercial laboratory culture result, and an in-house culture. Of 150 patient samples, 72 were positive by the rapid test, giving a prevalence of 48.0% versus 24.7% by traditional culture. Characterization of these results showed cross-reactivity with Enterococcus. The addition of bacitracin reduced this interference, and when reanalyzed, a colonization rate of 31.3% was found (P = 0.3961, chi-square), as well as a sensitivity of 100% (95% confidence interval [CI] 89.1-100) and a specificity of 93.6% (95% CI 86.9-97.2). The addition of bacitracin greatly improves the reliability of this diagnostic test and demonstrates a novel approach to reduce interference. An accurate determination of the test's sensitivity and specificity, however, awaits enrollment of the remaining subjects.