ORIGINAL ARTICLE Group B streptococcus colonization of pregnant women: comparative molecular and microbiological diagnosis Tarek A. A. Moussa & Rasha Hamed Elsherif & Youssef Abdelfattah Mohamed & Mohamed E. A. Dawoud & Asmaa Mohamed AboElAref Received: 29 March 2012 / Accepted: 27 June 2012 # Springer-Verlag London Limited 2012 Abstract This study aimed to compare the sensitivity of different culture methods from three different anatomic sites and to evaluate the sensitivity of polymerase chain reaction (PCR) assay targeting the 16 S ribosomal RNA gene in detection of group B streptococcus (GBS) colonization in pregnant women. From 100 pregnant women at 35–37 weeks of gestation, three cotton swabs were used to obtain vaginal, rectal, and rectovaginal (RV) specimens and plated onto Co- lumbia agar with colistin and nalidixic (CNA), group B strep- tococcus differential agar (GBSDA), and chromID Strepto B agar (CA), with and without Lim broth enrichment. PCR assay was done on the RV swabs. The overall GBS colonization rate was 29 % by culture and 31 % by PCR. GBS positivity for RV 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 74, 58, and 100 % of the carriers, respectively, whereas subculturing of Lim broth yielded 65, 59, and 83 % positivity, respectively. Using GBS culture as the “gold stan- dard,” the sensitivity of PCR was 100 %, and specificity was 97 %. We found that the inoculation of RV secretions directly onto CA is the most rapid, easy, and sensitive method than that of Lim broth enrichment. Also, we found that group B streptococci can be detected rapidly and reliably by a PCR assay of rectovaginal secretions from pregnant women. Keywords PCR . GBS . Rectovaginal . Culture Introduction Streptococcus agalactiae, group B streptococcus (GBS), is a significant cause of perinatal and neonatal infections world- wide. Rectovaginal colonization occurs in 10 to 30 % of pregnant women (Anthony et al. 1978; Boyer et al. 1983a; Dillon et al. 1982) and is responsible for 1.8 neonatal infections per 1,000 live births per year (CDC 1996a). It is possible to get infected with GBS during labor or in utero by transmission from maternal vaginal or anorectal colonized mucosa. There is another risk factor for GBS neonatal sepsis, which is prematurity, and mortality because GBS is higher in preterm compared to the number of newborns (Benitz 2002). Because results at 35–37 weeks correlate more closely with GBS colonization at term delivery, the Centers for Disease Control and Prevention (CDC) has recommended that all preg- nant women be screened for carriage of GBS between 35 and 37 weeks of gestation (CDC 2002), so that GBS positive women can receive antibacterial treatment (chemoprophylaxis) prior to delivery, to reduce mother-to-child transmission. Nowadays, prenatal screening by culture, in broth culture or selective me- dium, is considered the gold standard method for detection of anogenital GBS colonization (Dillon et al. 1982). To maximize GBS carriage detection rates, both the anatomic site of sampling and the culture methods used are important. Rectovaginal swabs have been reported to provide high bacterial yields, as the gastrointestinal tract is a natural reservoir for GBS and a potential source of vaginal colonization (CDC 2002; Dunne and Holland-Staley 1998; El Aila et al. 2009a; Philipson et al. 1995). The study was done in Cairo University, Egypt. R. H. Elsherif (*) Clinical and Chemical Pathology Department, Faculty of Medicine, Cairo University, Cairo, Egypt e-mail: whiterose_eg@yahoo.com T. A. A. Moussa : M. E. A. Dawoud : A. M. AboElAref Botany Department, Science Faculty, Cairo University, Cairo, Egypt Y. A. Mohamed Gynecology and Obstetrics Department, Cairo University, Cairo, Egypt Comp Clin Pathol DOI 10.1007/s00580-012-1555-x