Identification of pregnant women at risk of Streptococcus group B colonisation

The aims of the study were: 1) to evaluate the prevalence of recto-vaginal group B streptococci (GBS) colonisation using Todd Hewitt Broth - recommended by the Centers for Disease Control (CDC) - and Granada medium; 2) to establish the sensitivity and specificity of Granada medium for the detection of GBS colonisation; 3) to evaluate each vaginal Gram stained swab for bacterial vaginosis (BV) using Nugent criteria and for determining the amount of polymorphonuclear (PMN) leucocytes.

Eighty pregnant women between 35 and 40 gestation weeks hospitalised in the Department of Gynecology and Obstetrics, Medical University of Silesia, Poland, were included in the study. Two specimens were collected from each patient: one from the posterior vaginal fornix (Gram stain) and one from both vagina and anus to detect GBS colonisation. Each vaginal Gram stained swab was evaluated for BV using Nugent criteria as well as for PMN leucocyte count. To detect GBS colonisation, the liquid Todd Hewitt Broth, subsequently subcultured to blood agar and direct inoculation onto Granada medium, were used. Isolated GBS were identified by morphological features and by serological (Slidex Strepto-Kit, bioMerieux) and biochemical (rapid ID 32 Strep, bioMerieux) testing.

GBS colonisation was observed in 22 (27.8%) patients in both used media. Only in one case were GBS detected in Todd Hewitt Broth and not detected in Granada medium. The sensitivity and specificity of Granada medium were established as: 95.65% and 100%, respectively, compared with Todd Hewitt Broth recommended by CDC. Nugent criteria demonstrated 6.25% of cases of BV; in one case both BV and GBS colonisation were detected.

The selective Granada medium may be used concurrently with liquid Todd Hewitt Broth as a screening tool for prenatal group B streptococcal colonisation in pregnant women.