Background: Group B Streptococcus (GBS) colonization in pregnant women is a risk factor for causing infection in neonates; therefore, GBS screening tests are performed on them. Culture methods and molecular diagnostics are mainly performed for GBS detection; however, culture methods differ in the detection rate for GBS depending on the procedure of culture. The authors intended to confirm the difference in GBS colonization rate in the conventional culture method, enrichment culture method, and molecular genetic test as screening tests for GBS.
Methods: Duplicate vagino-rectal swabs were collected from 371 pregnant women between the 35th and 37th week of gestation; one was used for conventional culture method and the other was frozen at -80℃, followed by enrichment culture method and molecular genetic test.
Results: The prevalence of GBS colonization identified by conventional culture, enrichment culture, and molecular genetic test was 4.35% (17/391), 8.95% (35/391), and 22.25% (87/391), respectively. The detection rate by enrichment culture method was 2.06 times higher (17/391 vs. 35/391) than that by conventional culture method. It was identified that there was a significant difference in the detection rates of GBS between the two methods (p < 0.001). The detection rate identified in molecular genetic test was much higher at 22.25% (87/391). The concordance rate of the results from three detection methods for GBS was 80.05% (313/391). All pregnant women colonized with GBS were given intrapartum antibiotic prophylaxis using cefazolin and their neonates were confirmed not to be infected with GBS.
Conclusions: Prevalence of GBS colonization in pregnant women is shown to vary depending on detection method. Particularly, it differs greatly depending on the use of enrichment media in the culture method. Therefore, it is necessary that the microbiological laboratory implements the culture method with supplementary procedures such as selective or enrichment media in order to improve the detection rate of GBS.