Serum maternal cytokine levels as predictors of group B Streptococcus colonization at delivery

Abstract

Group B Streptococcus (Streptococcus agalactiae), is a β-hemolytic Gram-positive diplococci that has been found to colonize the genito-urinary tract of pregnant women. Maternal GBS colonization during pregnancy is a leading risk factor for neonatal GBS disease with approximately half of all newborns delivered from GBS colonized mothers developing invasive GBS disease. Apart from the culture and the polymerase chain reaction (PCR) methods recommended by Centres for Disease Control and Prevention, studies have shown that cytokines produced by the immune cells in response to the presence of bacteria may also be useful at detecting bacterial infections. The aim of the study was therefore to determine the clinical usefulness of maternal serum pro-and anti-inflammatory cytokine concentrations as a clinical index of intrapartum GBS colonisation. Mothers aged ≥18 years, who were HIV-negative, had vaginal deliveries and were not receiving antibiotic treatment were included in the study. Vaginal swabs and maternal blood were collected after delivery. Vaginal swabs were used to isolate GBS using culture, and PCR methods. Maternal serum samples were processed and used for cytokine analysis using high sensitivity premixed magnetic Luminex performance assays (R&D Systems system). A total of 122 participants were recruited for the study, out of which 35 (28.7 %) were found to be colonised with GBS. The 35 colonised mothers were identified either from a positive culture result or from a positive PCR result on the swab collected at the time of delivery. The most prevalent GBS serotype was serotype Ia, followed by serotype III. All the participants were young to middle aged women with a mean (SD) age of 26.5 (6) years (range: 18 to 43). Almost all the participants 117 (96%) were of black African ancestry. Overall, there were no significant differences in maternal characteristics such as age, race, middle upper arm circumference or gravidity between the two groups. The majority of the study participants delivered at full term gestation (≥ 37 weeks gestation). The infants were healthy with median Apgar scores of 9 and 10 at 1 and 5 minutes. None of the babies developed neonatal GBS disease within 90 days of birth. There were no significant differences in serum maternal IL-6 (P = 0.87, unpaired t test; t = 0.16), IL-8 (P = 0.19 unpaired t test; t = 1.48) and IL-10 (P = 0.95 unpaired t test; t = 0.06) concentrations in women colonised with GBS and women not colonised with GBS at delivery. Thus, measuring maternal serum IL-6, IL-8 and IL-10 may not be an appropriate clinical index of intrapartum GBS colonisation in healthy women.