Occurrence and detection method evaluation of group B streptococcus from prenatal vaginal specimen in Northwest China

Section: Introductionmentioning

confidence: 99%

Incidence and serotype characterisation ofStreptococcus agalactiaein a Portuguese hospital

et al. 2017

“…This method is shown to have comparable or even better sensitivity and specificity than standard Lim broth enrichment followed by blood agar cultures [17,27]. Using the carrot broth method, many studies have shown a prevalence of GBS in vaginal swabs in the range of 5-19.8 % in pregnant women [8,17,28]. In India, the prevalence of GBS is highly variable depending on the population studied or the methods used.…”

Section: Discussionmentioning

confidence: 99%

False-positive detection of Group B Streptococcus (GBS) in chromogenic media (Strep B Carrot Broth) due to presence of Enterococcus faecalis in High Vaginal swabs

Husein

Journal of Medical Microbiology

et al. 2022

Introduction. Vaginal colonization of Group B Streptococcus (GBS) is associated with preterm births and neonatal sepsis. Thus routine screening of GBS in prenatal care is recommended. Hypothesis. Chromogenic media (carrot broth) aids in specific and rapid detection of GBS. Aim. To investigate the efficiency of Strep B Carrot Broth for detection of GBS in high vaginal swabs from pregnant women. Methods. In this study 201 vaginal swab samples were collected from pregnant women. Swabs were inoculated in chromogenic media (Strep B Carrot Broth). The positive and negative cultures were inoculated on blood agar and crome agar plates. The colonies were subjected to 16S rRNA sequencing and gene-specific PCR for confirmation. The Christie Atkins Munch Peterson (CAMP) and bile esculin agar (BEA) tests were used for biochemical confirmation. PCR was performed on genomic DNA isolated from uncultured vaginal swabs. Results. It was found that 20/201 (9.9 %) vaginal swab samples were positive in the Strep B Carrot Broth and 17/20 (85 %) and 19/20 (95 %) of these samples yielded colonies on blood agar and crome agar, respectively. Of the 181 carrot broth-negative samples, 1 (0.5 %) and 38 (20.9 %) yielded colonies on blood agar and crome agar plates, respectively. However, 16 s rRNA sequencing revealed that none of the 20 carrot broth-positive cultures were GBS and had sequence similarities to Enterococcus faecalis . This was also confirmed by using gene-specific PCR and BEA positivity. Furthermore, E. faecalis was detected by PCR in DNA isolated from 57 uncultured vaginal swabs samples, GBS could only be detected by PCR in four samples. Conclusion. Carrot broth-based culture can lead to false-positive detection due to the presence of E. faecalis . Thus GBS-positive results in carrot broth must be confirmed by the other molecular and biochemical tests before making a final diagnosis.

“…This method is shown to have a sensitivity and specificity comparable or even better than the standard Lim broth enrichment followed by blood agar cultures (Block et al, 2008, Church et al, 2008. Using the Carrot Broth method, many studies have shown the prevalence of GBS in vaginal swabs in the range of 5 to 19.8% in pregnant women (Choi et al, 2021, Church et al, 2008, Xie et al, 2016. In India, the prevalence of GBS is highly variable depending on the population studied or the methods used.…”

Section: Discussionmentioning

confidence: 99%

“…GBS culture is normally performed on 5% Sheep Blood Agar (SBA) and colonies are detected by the breakdown of red blood cells that produce a characteristic zone of haemolysis. A confirmatory test for GBS is the Christie Atkins Munch Peterson (CAMP) test, or serotyping via an agglutinin reaction on selected β-haemolytic colonies (Rashwan, 2020, Xie et al, 2016. As an alternative to Blood agar, Crome agar is also used to detect GBS.…”

Section: Introductionmentioning

confidence: 99%

False-positive detection of Group B Streptococcus (GBS) in chromogenic media due to presence of Enterococcus faecalis in High Vaginal Swabs

Husein

et al. 2021

Preprint

Vaginal colonization of Group B Streptococcus (GBS) is associated with preterm births and neonatal sepsis. Thus, routine screening of GBS in prenatal care is recommended. Chromogenic media are useful in rapid and sensitive screening for GBS. herein, we evaluated the performance of Carrot broth for the detection of GBS in vaginal swabs of pregnant women. In all 20/201 (9.9%) vaginal swab samples were positive in the carrot broth. 17/20 (85%) and 19/20 (95%) samples yielded colonies on Blood agar and Crome agar respectively. However, 16s rRNA sequencing revealed that none of the carrot broth positive cultures had sequence similarities to the Enterococcus faecalis and not GBS. Furthermore, Enterococcus faecalis was detected by PCR in DNA isolated from the corresponding uncultured vaginal swabs samples, while GBS could be detected by PCR only in 4 samples. Thus carrot broth-based culture can lead to false-positive detection due to the presence of Enterococcus faecalis.