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.
Streptococcus agalactiae, usually termed group B streptococcus (GBS), is one of the most important causes of early-onset neonatal infection (1, 2). The incidence of neonatal GBS infection ranges from 0.80 to 3.06 per 1,000 live births in developing countries (1). Guidelines recommend screening vaginal or rectovaginal GBS colonization in pregnant women at 35 to 37 weeks of gestation (3, 4). The prevalence of rectovaginal colonization varies from 6.5 to 36% in European countries (5). For pregnant women colonized by GBS, intrapartum administration of antibiotics is recommended to prevent GBS transmission to the newborn during delivery (3, 4).The performance of microbiological methods for GBS screening has been greatly improved by the use of selective chromogenic media (6-9), together with rapid bacterial identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (10). The overnight broth preenrichment step, recommended in some countries (3, 4), increases the sensitivity of the GBS screening (8, 11), mostly in cases of low bacterial loads (11,12). Enriched and direct cultures were shown to have similar performances (9), although failure to perform direct culture can decrease sensitivity due to overgrowth of competing organisms in enrichment broth (13). Finally, nucleic acid amplification tests (NAATs), notably those including the extraction step, reduce the delay in results and could be used at the admission of pregnant women in active labor in order to administer adequate antibiotic prophylaxis (14, 15). NAATs offer similar performances compared to direct selective culture (16), but controversial results were reported after comparison with enriched culture (7,9,17,18). Recent guidelines advised the use of NAATs in selected circumstances, such as for term gestation women with unknown colonization status and no risk factors (3, 4).The aim of this study was to assess the performance of the new Brilliance GBS chromogenic medium (Thermo Fisher Scientific, Dardilly, France) for the detection of S. agalactiae compared to those of two commercially available chromogenic media selective for this bacterium, ChromID STRB and Granada media (bioMérieux, Marcy l'Etoile, France).From February to April 2013, 760 vaginal swabs (ESwab 480CE; Copan, Brescia, Italy) from pregnant women were sent to the microbiology department of the University Hospital of SaintEtienne, France. The routine screening of GBS in pregnant women was performed by direct culture following French recommendations (19). Approximately 50 l of ESwab medium was deposited on Granada medium by using the swab and spread with a sterile loop. Plates were incubated...