Evaluation of the BD MAX GBS assay to detect Streptococcus group B in LIM broth–enriched antepartum vaginal–rectal specimens

Applicability of an in-house extraction protocol in a Bruker Biotyper matrix-assisted laser desorption/ionization time-of-flight mass spectrometry system for the identification of Streptococcus agalactiae from broth-enriched vaginal/rectal swab specimens

BACKGROUND AND PURPOSE

Early laboratory identification of group B Streptococcus (GBS, Streptococcus agalactiae) in the birth canal of pregnant women is critical for prompt administration of antimicrobial therapy and may further reduce the mortality rate due to GBS neonatal infection.

METHODS

A total of 164 vaginal/rectal swab specimens collected from pregnant women at 35-37 weeks of gestation were screened for GBS vaginal colonization. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS, Bruker Biotyper, Bruker Daltonik GmbH, Bremen, Germany) system was used to detect GBS from Carrot broth and LIM broth enrichment using an in-house extraction protocol. The results were compared to those by conventional broth-enriched culture/identification methods as the gold standard. BD MAX™ GBS assay (Becton Dickinson, Sparks, MD, USA) was also performed for Carrot broth-enriched specimen. Discordant results were investigated using the GeneXpert® GBS PCR assay (Cepheid Inc., Sunnyvale, CA, USA).

RESULTS

Using the extraction protocol, 33 (20.1%) of the 164 specimens were positive in Carrot broth, and 19 (11.6%) were positive in LIM broth. Using the culture protocol, 38 (23.2%) samples in Carrot broth and 35 (21.3%) in LIM broth were positive. The sensitivity, specificity, and positive and negative predictive values using the extraction protocol in Carrot broth and LIM broth compared to the gold standard conventional culture/identification method were 86.8% and 50.0%, 100% and 100%, 100% and 100%, and 96.2% and 86.9%, respectively.

CONCLUSIONS

The extraction protocol with MALDI-TOF MS from Carrot broth-enriched samples provides a more rapid turnaround time, lower cost, and acceptable sensitivity and specificity to correctly identify pathogens when compared to conventional culture/identification methods.

An Application of Real-Time PCR and CDC Protocol May Significantly Reduce the Incidence of Streptococcus agalactiae Infections among Neonates

Streptococcus agalactiae is an important human opportunistic pathogen, especially infectious for pregnant women and neonates. This pathogen belongs to beta hemolytic Streptococcus spp. representatives and accounts for a significant part of early infections in newborns, including serious life-threatening infections. This research investigated the usefulness of Centers for Disease Control and Prevention (CDC) protocol for S. agalactiae DNA detection in 250 samples of recto-vaginal swabs collected from pregnant women (at 35-37 weeks of gestation) and pre-cultured overnight in liquid medium. With an application of the CDC protocol-based real-time PCR, the cfb gene was detected in 68 (27.2%) samples compared to 41 (16.4%) for the standard culture-based methodology. The applied molecular method presented high sensitivity (100.0%) and specificity (87.1%). Therefore, it allowed for more precise detection of S. agalactiae bacteria, compared to the reference diagnostic method, culture on solid media with the following strain identification. The increased sensitivity of GBS detection may result in a reduced number of infections in newborns and leads to more targeted antimicrobial prophylaxis therapy of GBS infections in pregnant women. In addition, the use of the molecular method allows for a significant reduction in the time needed to obtain a result for GBS detection, and interpretation of the results is relatively simple. Therefore, it enables a faster intervention in case of a necessity of an antibiotic therapy introduction in pregnant women whose GBS status is unknown at the time of delivery.

Retrospective Study for the Clinical Evaluation of a Real-Time PCR Assay with Lyophilized and Ready-to-Use Reagents for Streptococcus agalactiae Detection in Prenatal Screening Specimens

Streptococcus agalactiae is a leading cause of sepsis and meningitis in newborns and young infants. Screening programs and intrapartum antibiotic prophylaxis have reduced early neonatal onset of disease. The aim of this study was to evaluate a molecular assay with lyophilized and ready-to-use reagents: VIASURE® Streptococcus B Real Time PCR detection kit (CerTest Biotec) (Viasure qPCR assay) compared to both the GBS culture and a molecular assay with separated and frozen reagents: Strep B Real-TM Quant (Sacace Biotecnologies®) (Sacace qPCR assay). A total of 413 vaginal−rectal swabs from women between the 35th and 37th weeks of pregnancy were processed. GBS culture was firstly achieved through Granada medium and Columbia CNA agar at 35 °C in aerobic conditions. Then, nucleic acid extraction was performed for subsequent molecular analysis using both commercial assays. Discordant results were resolved via bidirectional Sanger sequencing. Viasure qPCR assay clinical sensitivity was 0.97 (0.92−0.99) and specificity 1 (0.98−1). This retrospective study demonstrated the good clinical parameters and the strong overall agreement (99.3%) between the Viasure qPCR assay and both reference assays. Finally, the added value observed of the assay under study was the stabilized and ready-to-use format, reducing the number of time-consuming steps, permitting the storage at room temperature, facilitating transport, being environmentally respectful, and reducing additional costs.

Performance of BD MAX Group B Streptococcus (GBS) Assay without Enrichment for the Detection of GBS

Group B streptococcus (GBS) is an important pathogen causing neonatal early-onset disease. We evaluated the diagnostic performance of BD Max GBS assay (Becton Dickinson, Franklin Lakes, NJ, USA) without enrichment (direct BDM) for detecting GBS using vaginal and rectal specimens in comparison with culture. In total, 716 specimens collected from 358 pregnant women between June 2018 and May 2020 were included in this study. Bacterial culture was performed using ChromID Strep B agar (bioMérieux, Marcy-l’Étoile, France), and species identification results were confirmed using the VITEK-MS system (bioMérieux). The sensitivity of direct BDM for vaginal and rectal specimens was 75.0% and 100%, respectively. Thirteen specimens showed discrepant results: 10 false-negative results in the vaginal specimens and three false-positive results in the rectal specimens. The overall agreement between direct BDM and culture was 98.9% (354/358). The final sensitivity and specificity of direct BDM were 98.5% and 99.0%, respectively. Discrepant results—one false-negative and three false-positives—were obtained for four specimens. Direct BDM shows a good diagnostic performance and will be useful for GBS screening within a few hours.

Application of the appropriate molecular biology-based method significantly increases the sensitivity of group B streptococcus detection results

BACKGROUND

Streptococcus agalactiae (group B streptococcus: GBS) is a leading cause of early- and late-onset diseases in neonates. Reliable results of GBS carriage investigation among pregnant women may decrease the incidence of neonatal infection and mortality.

AIM

To compare the results of conventional culture investigation with those of the US Food and Drug Administration-approved nucleic acid amplification test (BD Max GBS (Becton Dickinson)), and to establish our own protocols of standard polymerase chain reaction (PCR).

METHODS

A total of 250 vaginal-rectal swabs from three different hospitals in Bydgoszcz, Poland, were used to evaluate GBS carriage. Standard laboratory technique (overnight culture in broth enrichment media) results were compared with those of BD Max GBS assay (Becton Dickinson) and two standard PCR protocols, established to detect the cfb and 16S rRNA S. agalactiae genes, from the overnight cultures of the samples in the liquid enrichment media.

FINDINGS

The overall GBS carriage was estimated as 16.4-23.2%, depending on the applied detection method. The highest percentage of positive results, from each lab-oratory was obtained with the application of BD Max GBS assay. The differences in the number of positive results obtained with this particular method were statistically significant. Overall, 27 discrepancies were noted for the results obtained with the application of the methods compared.

CONCLUSIONS

The methods applied for GBS detection differ in sensitivity. A culture technique, though very specific, appears to be less sensitive at detecting S. agalactiae compared with the commercially available BD Max GBS assay or in-house PCR protocols established for this purpose.

Comparison of Three Nucleic Acid Amplification Tests and Culture for Detection of Group B Streptococcus from Enrichment Broth

Colonization of the gastrointestinal and genitourinary tracts of pregnant women with group B Streptococcus (GBS) can result in vertical transmission to neonates during labor/delivery. GBS infections in neonates can cause severe complications, such as sepsis, meningitis, and pneumonia. Accurate detection is critical because administration of intrapartum antibiotics can significantly reduce transmission. We compared the clinical sensitivities of three nucleic acid amplification tests (NAATs), the Hologic Panther Fusion GBS, Luminex Aries GBS, and Cepheid Xpert GBS LB assays, to that of the standard of care culture method recommended for GBS screening using 500 vaginal-rectal swab specimens after 18 to 24 h of broth enrichment. We identified 108 positive specimens (21.6%) by culture, while at least 1 of the 3 NAATs was positive for GBS in 155 specimens (31.0%). All 108 specimens positive by culture were also detected by the Panther Fusion assay, while 107/108 (99.1%) were detected by the Cepheid Xpert and Luminex Aries assays. Of the 61 specimens positive by at least 1 NAAT but negative by culture, 24 (39.3%) were positive by all 3 NAATs, suggesting that they represent true positives (TPs). NAATs offer less hands-on time, greater throughput, faster time to result, and potentially greater sensitivity than culture methods, and they should be considered the new gold standard for intrapartum GBS screening.

Multicenter Evaluation of NeuMoDx Group B Streptococcus Assay on the NeuMoDx 288 Molecular System

Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis in developed countries. Recommendations for antepartum GBS detection include enriched culture with several options for identifying GBS, some of which are time-consuming. To reduce the time for identification and determination of the maternal GBS colonization status, rapid nucleic acid amplification technologies have been developed and commercialized. For rapid detection of GBS, a three-site clinical study was conducted to evaluate the NeuMoDx GBS assay, a real-time PCR test performed for vaginal/rectal swab specimens in Lim broth enrichment culture on the NeuMoDx 288 molecular system (NeuMoDx system); these data were used to a support 510(k) submission. A total of 1,250 eligible remnant samples were prospectively enrolled and tested during the study. The results of the PCR assay were compared to the results of the Centers for Disease Control and Prevention (CDC)-recommended enriched-culture method, which served as the gold standard reference method for the study. The NeuMoDx GBS assay results yielded a sensitivity of 96.9% (95% confidence interval [CI] = 94.1 to 98.4), specificity of 96.0% (95% CI = 94.6 to 97.1), and a total agreement with the reference method of 96.2% (95% CI = 93.8 to 98.3). NeuMoDx GBS assay results were also compared to results obtained using the BD MAX GBS assay on the BD MAX system. The two systems demonstrated a total percent agreement of 98.0% (95% CI = 95.5 to 100.0). The performance of the NeuMoDx GBS assay implemented on the NeuMoDx system compared favorably to the CDC enriched-culture method and to the BD MAX GBS assay.

Detection and genomic analysis of genital group B streptococcus in pregnant Korean women

AIM

Group B streptococcus (GBS) is a leading cause of life-threatening bacterial infections among newborns, and neonates born to heavily colonized women may be subject to vertical transmission. We sought to determine an appropriate detection method for genital GBS in pregnant women by comparing culture-based methods and real-time polymerase chain reaction (PCR). In addition, we performed molecular serotyping and multilocus sequence typing (MLST) on isolates.

METHODS

A total of 150 pregnant women were enrolled and underwent vaginal-rectal swabbing at 16-40 weeks of gestation. GBS was identified by conventional culture and real-time PCR with or without enrichment. Molecular serotyping and MLST were performed on isolates.

RESULTS

Overall genital GBS positive rate among the 150 study subjects was 17.3%. Direct culture identified 18 (12.0%) positive specimens, enrichment culture 22 (14.6%), direct PCR 24 (16.0%) and enrichment PCR 25 (16.6%). The sensitivity and specificity by direct and enrichment PCR were as follows: for direct PCR, 90.9% and 96.9%, respectively; and for enrichment PCR, 95.5% and 96.9%, respectively. Resistance rates to clindamycin and erythromycin were 33.3% and 19.1%, respectively. Serotype III-1 was the most common (26.3%), followed by serotype Ib (21.1%), III-3 (15.8%), V (15.8%), II (10.5%), IV (5.3%) and VI (5.3%). Most common sequence types (ST) were ST-1, ST-19 and ST-862 (15.8%), followed by ST-2 and ST-654 (10.5%).

CONCLUSION

Direct real-time PCR using vaginal-rectal specimen could be used for detecting GBS in emergent conditions. Molecular serotypes III, Ib and V were most common. MLST analysis frequently presented ST-1, ST-19 and ST-862.

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.

Evaluation of StrepBSelect Chromogenic Medium and the Fast-Track Diagnostics Group B Streptococcus (GBS) Real-Time PCR Assay Compared to Routine Culture for Detection of GBS during Antepartum Screening

Life-threatening infection in neonates due to group B Streptococcus (GBS) is preventable by screening of near-term pregnant women and treatment at delivery. A total of 295 vaginal-rectal swabs were collected from women attending antepartum clinics in Calgary, Alberta, Canada. GBS colonization was detected by the standard culture method (Strep B Carrot Broth subcultured to blood agar with a neomycin disk) and compared to recovery with Strep Group B Broth (Dalynn Biologicals) subcultured to StrepBSelect chromogenic medium (CM; Bio-Rad Laboratories) and the Fast-Track Diagnostics GBS real-time PCR (quantitative PCR [qPCR]) assay (Phoenix Airmid Biomedical Corp.) performed with broth-enriched samples and the Abbott m2000sp/m2000rt system. A total of 62/295 (21%) women were colonized with GBS; 58 (19.7%) cases were detected by standard culture, while CM and qPCR each found 61 (20.7%) cases. The qPCR and CM were similar in performance, with sensitivities, specificities, and positive and negative predictive values of 98.4 and 98.4%, 99.6 and 99.6%, 98.4 and 98.4%, and 99.6 and 99.6%, respectively, compared to routine culture. Both qPCR and CM would allow more rapid reporting of routine GBS screening results than standard culture. Although the cost per test was similar for standard culture and CM, the routine use of qPCR would cost approximately four times as much as culture-based detection. Laboratories worldwide should consider implementing one of the newer methods for primary GBS testing, depending on the cost limitations of different health care jurisdictions.

Comparison of the AmpliVue, BD Max System, and illumigene Molecular Assays for Detection of Group B Streptococcus in Antenatal Screening Specimens

The performances of the AmpliVue, BD Max, and illumigene group B Streptococcus (GBS) nucleic acid amplification tests (NAATs) were compared to that of enriched culture for detection of GBS in antenatal screening specimens. Two hundred specimens were tested simultaneously with the NAATs, following 18 to 24 h of Lim broth enrichment; 15% of specimens were culture positive for GBS, whereas 31.5% were positive by at least one NAAT. All three NAATs were more sensitive (sensitivity, 90.9 to 100%) than culture (sensitivity, 53.6%).

Direct identification of Streptococcus agalactiae and capsular type by real-time PCR in vaginal swabs from pregnant women

Most group B streptococcus (GBS) infections in newborns are with capsular type Ia, Ib, or III. To prevent these infections more effectively, we developed a real-time PCR method to simultaneously detect GBS species and identify these 3 capsular types in vaginal swab samples from women at 36-39 weeks of gestation. DNA to be detected included those of the dltS gene (encoding a histidine kinase specific to GBS) and cps genes encoding capsular types. PCR sensitivity was 10 CFU/well for a 33-35 threshold cycle. Results were obtained within 2 h. Direct PCR results were compared with results obtained from cultures. Samples numbering 1226 underwent PCR between September 2008 and August 2012. GBS positivity rates by direct PCR and after routine culture were 15.7% (n = 192) and 12.6% (n = 154), respectively. Sensitivity and specificity of direct PCR relative to culture were 96.1% and 95.9%. Of GBS positive samples identified by PCR, capsular types determined directly by real-time PCR were Ia (n = 24), Ib (n = 32), and III (n = 26). Real-time PCR using our designed cycling probe is a practical, highly sensitive method for identification of GBS in pregnant carriers, allowing use of prophylactic intrapartum antibiotics in time to cover the possibility of unexpected premature birth.

Antepartum screening for group B Streptococcus by three FDA-cleared molecular tests and effect of shortened enrichment culture on molecular detection rates

Neonatal Streptococcus agalactiae infections cause significant morbidity and mortality, and antenatal screening is recommended. We compared three U.S. Food and Drug Administration (FDA)-cleared nucleic acid amplification tests (NAATs) to culture using 314 vaginal/rectal swabs after 18 to 24 h (recommended period) and 4 to 8 h (shortened period) of broth enrichment. Agreement of the NAATs with each other was high (97.1% to 98.4%), but culture was less sensitive than all NAATs (67% to 73%). A shortened period of broth culture enrichment resulted in 1 false-negative result in 68 (1.5%). The NAATs performed comparably and were more sensitive than culture.

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.

Clinical evaluation of the walk-away specimen processor and ESwab for recovery of Streptococcus agalactiae isolates in prenatal screening specimens

Rectal/vaginal specimens (n = 97) were collected in parallel using ESwab and Liquid Stuart (LS) rayon fiber wrapped swab collection devices. Each collection device was used to directly inoculate culture medium and LIM broth. Medium inoculation by ESwab was conducted using the Walk-Away specimen processor (WASP). Medium inoculation by the LS device was conducted manually. The sensitivities of ESwab and LS upon direct plating were 93.8% and 87.5%, respectively, and increased to 96.9% and 90.6%, respectively, following broth enrichment.

Accuracy of an accelerated, culture-based assay for detection of group B streptococcus

OBJECTIVE

To determine the validity of a novel Group B Streptococcus (GBS) diagnostic assay for the detection of GBS in antepartum patients.

STUDY DESIGN

Women were screened for GBS colonization at 35 to 37 weeks of gestation. Three vaginal-rectal swabs were collected per patient; two were processed by traditional culture (commercial laboratory versus in-house culture), and the third was processed by an immunoblot-based test, in which a sample is placed over an antibody-coated nitrocellulose membrane, and after a six-hour culture, bound GBS is detected with a secondary antibody.

RESULTS

356 patients were evaluated. Commercial processing revealed a GBS prevalence rate of 85/356 (23.6%). In-house culture provided a prevalence rate of 105/356 (29.5%). When the accelerated GBS test result was compared to the in-house GBS culture, it demonstrated a sensitivity of 97.1% and a specificity of 88.4%. Interobserver reliability for the novel GBS test was 88.2%.

CONCLUSIONS

The accelerated GBS test provides a high level of validity for the detection of GBS colonization in antepartum patients within 6.5 hours and demonstrates a substantial agreement between observers.

Comparison of the GenMark Diagnostics eSensor respiratory viral panel to real-time PCR for detection of respiratory viruses in children

A novel eSensor respiratory viral panel (eSensor RVP) multiplexed nucleic acid amplification test (GenMark Diagnostics, Inc., Carlsbad, CA) was compared to laboratory-developed real-time PCR assays for the detection of various respiratory viruses. A total of 250 frozen archived pediatric respiratory specimens previously characterized as either negative or positive for one or more viruses by real-time PCR were examined using the eSensor RVP. Overall agreement between the eSensor RVP and corresponding real-time PCR assays for shared analytes was 99.2% (kappa = 0.96 [95% confidence interval {CI}, 0.94 to 0.98]). The combined positive percent agreement was 95.4% (95% CI, 92.5 to 97.3); the negative percent agreement was 99.7% (95% CI, 99.4 to 99.8). The mean real-time PCR threshold cycle (C(T)) value for specimens with discordant results was 39.73 (95% CI, 38.03 to 41.43). Detection of coinfections and correct identification of influenza A virus subtypes were comparable between methods. Of note, the eSensor RVP rhinovirus assay was found to be more sensitive and specific than the corresponding rhinovirus real-time PCR. In contrast, the eSensor RVP adenovirus B, C, and E assays demonstrated some cross-reactivity when tested against known adenovirus serotypes representing groups A through F. The eSensor RVP is robust and relatively easy to perform, it involves a unique biosensor technology for target detection, and its multiplexed design allows for efficient and simultaneous interrogation of a single specimen for multiple viruses. Potential drawbacks include a slower turnaround time and the need to manipulate amplified product during the protocol, increasing the possibility of contamination.