|Thornberry, md, James|
|Kay, md, Helen|
Submitted to: American Journal of Obstetrics and Gynecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/16/2003
Publication Date: 9/1/2002
Citation: BENSON, K.D., ELLIOT, J.A., DEGNAN, A.J., WILLENBERG, H.J., THORNBERRY, MD, J., KAY, MD, H.H., LUCHANSKY, J.B. PULSED FIELD FINGERPRINTING OF VAGINAL GROUP B STREPTOCOCCUS IN PREGNANCY: CORRELATION OF RESTRICTION PROFILES WITH SEROTYPE. AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY. 2002. Interpretive Summary: Group B Streptococcus (GBS) infection is the most common cause of sepsis in newborns in both North America and Europe, with about 14 to 40 percent of pregnant women being asymptomatic carriers. The current standard of care dictates antibiotic coverage in labor for patients with screen positive cultures for GBS, but the widespread use of antibiotics and the emergence of antibiotic-resistant isolates of GBS are a real concern with this type of treatment. There are five serotypes of GBS that are associated with early-onset disease, but only one of these serotypes is most often associated with neonatal late-onset sepsis and meningitis. However, identification of GBS by serotyping is currently not possible on a clinical basis due to costs and time constraints. For these reasons, we investigated the ability of a technique called pulsed-field gel electrophoresis (PFGE) to derive a fingerprint or bar code for a given strain of GBS as a means to identify serotypes or isolates that are more likely to cause infection. In so doing, we were able to show that among 42 maternal isolates that 8 serotypes were represented and that these displayed 25 unique fingerprints. Likewise, among 20 mother::baby paired isolates, 6 serotypes were represented that displayed 9 unique fingerprints. From these findings we concluded that PFGE is a more efficient, reproducible, and highly discriminating method for further characterizing GBS compared with serotyping. These data suggest that PFGE could be a useful tool for selecting patients to treat with antibiotics who would be at highest risk of neonatal sepsis and meningitis due to the type of GBS they were harboring.
Technical Abstract: Management protocols for vaginal group B beta-hemolytic streptococci (GBS; Streptococcus agalactiae) infection during pregnancy focus on treatment after an infection is identified. However, there is more to be learned about the epidemiology of GBS infections during pregnancy. In this study, we compared the discriminatory capability of pulsed field gel electrophoresis (PFGE) with serotyping on 42 vaginal isolates cultured from pregnant patients in their third trimester and 20 mother::baby paired isolates from patients with documented newborn GBS infection. Isolates were serotyped by the Lancefield capillary precipitin method and molecularly subtyped by contour clamped homogeneous electric field PFGE. Nine of the 13 known seroytpes of GBS (Ia, Ia/c, Ib, Ib/c, II, IIc, III, V, and NT/c) were represented among the 62 isolates tested. Among the 42 maternal isolates, 8 serotypes were represented and among the 20 mother::baby paired isolates, 6 serotypes were represented. The serotypes of the mother::baby paired isolates matched in 9 of the 10 pairs tested. Pulsed field analyses revealed 25 unique restriction profiles among the 42 material isolates that could be arranged into 5 major groups based on their overall relatedness. Each group was comprised of one predominant serotype. The 20 mother::baby paired isolates displayed 9 unique pulsed field profiles, and 9 of the 10 showed indistinguishable profiles between the mother and baby isolates. These findings substantiate that PFGE is more discriminating than serotyping for further characterizing GBS in a clinical setting because of the different, yet closely related, restriction profiles within a PFGE cluster of strains that are linked to one specific serotype. Thus, the technique of PFGE allows for better delineation of genomic subtypes of GBS colonizing pregnant women and/or their infected newborn and this could help to refine their treatment protocol. Patients carrying a strain or serotype of GBS that may be more likely to cause infection may be suitable candidates for antibiotic treatment and/or prophylaxis. This in turn will lead to more prudent use of antibiotics and most likely reduce the numbers and types of GBS that may become resistant to antibiotics.