Comparison of different sampling techniques and of different culture methods for detection of group B streptococcus carriage in pregnant women

Abstract

BackgroundStreptococcus agalactiae (group B streptococcus; GBS) is a significant cause of perinatal and neonatal infections worldwide. To detect GBS colonization in pregnant women, the CDC recommends isolation of the bacterium from vaginal and anorectal swab samples by growth in a selective enrichment medium, such as Lim broth (Todd-Hewitt broth supplemented with selective antibiotics), followed by subculture on sheep blood agar. However, this procedure may require 48 h to complete. We compared different sampling and culture techniques for the detection of GBS.MethodsA total of 300 swabs was taken from 100 pregnant women at 35-37 weeks of gestation. For each subject, one rectovaginal, one vaginal and one rectal ESwab were collected. Plating onto Columbia CNA agar (CNA), group B streptococcus differential agar (GBSDA) (Granada Medium) and chromID Strepto B agar (CA), with and without Lim broth enrichment, were compared. The isolates were confirmed as S. agalactiae using the CAMP test on blood agar and by molecular identification with tDNA-PCR or by 16S rRNA gene sequence determination.ResultsThe overall GBS colonization rate was 22%. GBS positivity for rectovaginal sampling (100%) was significantly higher than detection on the basis of vaginal sampling (50%), but not significantly higher than for rectal sampling (82%). Direct plating of the rectovaginal swab on CNA, GBSDA and CA resulted in detection of 59, 91 and 95% of the carriers, respectively, whereas subculturing of Lim broth yielded 77, 95 and 100% positivity, respectively. Lim broth enrichment enabled the detection of only one additional GBS positive subject. There was no significant difference between GBSDA and CA, whereas both were more sensitive than CNA. Direct culture onto GBSDA or CA (91 and 95%) detected more carriers than Lim broth enrichment and subculture onto CNA (77%). One false negative isolate was observed on GBSDA, and three false positives on CA.ConclusionsIn conclusion, rectovaginal sampling increased the number GBS positive women detected, compared to vaginal and/or rectal sampling. Direct plating on CA and/or GBSDA provided rapid detection of GBS that was at least as sensitive and specific as the CDC recommended method of Lim broth subcultured onto non chromogenic agar.

Group B Streptococcus detection in pregnant women via culture and PCR methods

“…Studies investigating GBS in vaginal samples alone detected prevalence rates ranging between 11% and 19.8%, whereas recto-vaginal cultures reveal higher colonization rates, varying between 22% and 29.5% 8,[23][24][25] . In this study, the GBS isolation rates increased by 18.4% and 20.5% for the culture and PCR methods, respectively, when perianal samples were included in the analysis.…”

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

“…Cultures performed in the early third trimester have a relatively low predictive value in identifying women colonized at term [5]. Collection of samples from both the lower vagina and rectum through the anal sphincter provides significantly higher yield than does collection of vaginal samples alone [1,2].…”

Strong Correspondence of the Vaginal and Rectal Load of Group B Streptococci in Pregnant Women

“…Several culture-based studies have reported higher carriage rates of GBS in the rectum than in the vagina [18,26,27], supporting the idea that the gastrointestinal tract is the reservoir for vaginal GBS. Meyn et al [28] showed that rectal colonization with GBS was the most significant predictor of vaginal colonization, suggesting that the vagina becomes colonized with GBS as a result of transfer of the organism from the rectum to the vagina.…”

“…Differences in colonization rates can also be attributed to variation in the culture and detection methods employed, including the media selected and collection sites used [17][18][19]. The aim of this study was to quantify group B streptococci in the vagina and rectum and to determine whether GBS loads in both sites corresponded, as an indication of the rectum as a reservoir of vaginal GBS.…”

“…In a previous study, we showed that, to maximize GBS carriage detection rates, both the anatomic site of sampling and the culture methods used are important [18]. In that study, we compared three sampling techniques, namely rectovaginal swabbing, vaginal swabbing only and rectal swabbing only, using the Eswab, and we concluded that for culture, rectovaginal sampling increased the number of GBS positive women detected, compared to vaginal and/or rectal sampling, namely the number of GBS positive women on the basis of rectovaginal swabbing (n = 22) was significantly higher than the number of GBS positive women on the basis of vaginal sampling (n = 11), and higher than the number on the basis of rectal sampling (n = 18) [18].…”